D N F T R T P B

P -L/D- (PLDLA) / SAn experimental ex vivo study

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Helsinki 2008

e Department of Hand Surgery and Department of Orthopaedics and Traumatology,

Helsinki University Central Hospital, University of Helsinki, and the Institute of Biomaterials, Tampere University of Technology, Finland

D N F T R T P B

P -L/D- (PLDLA) / SAn experimental ex vivo study

A V

Academic Dissertation

To be presented, with the permission of the Faculty of Medicine of the University of Helsinki, for public examination in the auditorium of Töölö Hospital,

on June 6th, 2008, at 12 noon.

Helsinki 2008

S :

Emeritus Professor Pentti Rokkanen, M.D., Ph.D., Ph.D. (Hon. Vet. Med)Department of Orthopaedics and TraumatologyHelsinki University Central HospitalUniversity of Helsinki, Helsinki, Finland

Docent Timo Raatikainen, M.D., Ph.D.Department of Hand SurgeryHelsinki University Central HospitalUniversity of Helsinki, Helsinki, Finland

R :

Docent Martti Vastamäki, M.D., Ph.D.University of Turku, Turku, FinlandDepartment of Hand SurgeryInvalid Foundation Hospital, Helsinki, Finland

Docent E. Antero Mäkelä, M.D., Ph.D.University of Helsinki, Helsinki, FinlandNational Authority for Medicolegal A airs

O :

Docent Heikki Jaroma, M.D., Ph.D.University of Kuopio, Kuopio, Finland

ISBN 978-952-92-3851-4 (paperback)ISBN 978-952-10-4698-8 (PDF)

Helsinki University Printing HouseHelsinki 2008

As time is measured by the pendulumunfailingly in oscillationsSo ethics and scienceFrom inspiration to experienceUnfailingly change throughout times. (Goethe)

CONTENTS

ABSTRACT 7

LIST OF ORIGINAL PUBLICATIONS 9

ABBREVIATIONS 10

INTRODUCTION 11

REVIEW OF THE LITERATURE 13

1. A 13 1.1. Macroscopic anatomy of the exor tendons and pulley system 13 1.2. Histology and biochemical composition 14 1.3. Vasculature and nutrition 15

2. B 16 2.1. Tendon strength 16 2.2. Forces during nger exion 16 2.3. Tendon excursion 16

3. T 17 3.1. Biomechanical testing methods 17 3.2. Properties of the tendon repair 19 3.3. Core suture 20 3.3.1. Number of strands 20 3.3.2. Loop con guration 23 3.3.2.1. Locking versus grasping loop 3.3.2.2. Type and size of locking loop 3.3.3. Core suture purchase 25 3.3.4. Suture calibre 25 3.3.5. Volar versus dorsal placement of sutures 26 3.3.6. Placement of the knots 26 3.3.7. Suture materials 27 3.3.7.1. Biomechanical properties 3.3.7.2. Biocompatibility 3.4. Tendon repair devices 29 3.5. Peripheral suture techniques 29 3.6. Gliding resistance of tendon repairs 30

4. T 32 4.1. General healing process 32 4.2. Adhesion formation 33 4.3. In uence of mobilization on tendon healing 34 4.3.1. Experimental studies in vivo 34 4.3.2. Clinical studies 35

5. P 375.1. Chemical properties 37

5.2. Biodegradation 38 5.3. Biocompatibility 38

Table 1 40Table 2 50

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AIMS OF THE STUDY 52

MATERIALS AND METHODS 53

1. T 53

2. S 53

3. R 53

4. K 57

5. B 57 5.1. Static tensile testing 57 5.1.1. Material testing 58 5.1.2. Knot testing 59 5.1.3. Tendon repair testing 59 5.2. Cyclic tensile testing 60

6. M 60

7. S 60

RESULTS 62

1. D (I) 62

1.1. Mode of failure of the repairs 62 1.2. e number of strands 62 1.3. e suture calibre 62 1.4. e suture con guration 62

2. M PLDLA / (T ®) (II) 66

2.1. Biomechanical properties of the suture materials 66 2.2. Biomechanical knot properties 68 2.3. Morphometrical analysis of the secure knots 70

3. T - - P K (III) 70

3.1. Width of the sutures 70 3.2. Mode of failure of the repairs 70 3.3. Force, strain, and sti ness of the repairs 70

4. B PLDLA / - P K (IV) 71

4.1. Mode of failure of the repairs 71 4.2. Static and cyclic testing 71

DISCUSSION 74

SUMMARY AND CONCLUSIONS 80

ACKNOWLEDGEMENTS 83

REFERENCES 85

ORIGINAL PUBLICATIONS 99

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ABSTRACT

Postoperative early active motion improves the outcome a er exor tendon repair in the hand compared to passive mobilization. Active motion, however, enhances the forces subjected to the repair increasing the biomechanical requirements to prevent gap formation and repair rupture. Multi-strand repair techniques have been developed to withstand the forces of active motion, but they are technically demanding and increase tendon handling, which limits their clinical application.

Non-absorbable suture materials such as coated braided polyester are commonly used in exor tendon repair. e advantage of bioabsorbable suture material is gradual absorption

from the tissue, but they are not usually used in exor tendon repair due to lack of su cient tensile strength half-life and fear of increased tissue reaction and adhesion formation. e bioabsorbable poly-L/D-lactide (PLDLA) 96/4 has experimentally demonstrated a tensile strength half-life su cient for exor tendon healing and good biocompatibility in the exor tendon in vivo.

e present biomechanical experiments ex vivo were planned to develop a new exor tendon core suture technique which is strong enough and yet simple to perform using the bioabsorbable PLDLA 96/4 suture to meet the biomechanical requirements of early active mobilization. e strength of the tendon repair is dependent on the material strength, suture knots, and the holding capacity of the repair technique of the tendon. To improve the strength of the intact tendon repair, di erent components contributing to the repair strength need to be evaluated.

e initiation of the disruption and the pattern of the failure of the tendon repair composite during static tensile testing as well as the in uence of the di erent structural properties of the core suture on the strength of the intact repair were investigated in ve core sutures which were variations of the Pennington modi ed Kessler and Savage techniques. e repairs were compared as paired to evaluate the in uence of 1) the number of strands, 2) suture con guration, and 3) suture calibre. In all repairs visible failure was initiated by rupture of the simple running peripheral suture in the proximity of the yield point of the load-deformation curve. us, the yield force can be regarded as the maximum strength of the intact repair composite. Varying the structural properties of the core suture in uenced the strength of the intact repair. Increasing the number of strands signi cantly improved the sti ness and yield force of the intact repair as well as the gap forces and ultimate force in the Pennington modi ed Kessler and Savage con gurations. e suture con guration and suture calibre did not in uence the strength and sti ness of the intact repair in the studied techniques. However, the failure of the 4-0 suture repairs occurred by suture rupture, while the 3-0 suture repairs failed by suture pullout, rupture or a combination of both indicating that the strength of the 3-0 suture and the holding capacity of the repair techniques of the tendon were close to each other. us, further increase in the strength of the intact Pennington modi ed Kessler and simple running peripheral suture composite necessitates improving the holding capacity of the locking loops of the tendon.

On the basis of the above results, a triple-stranded suture and triple-stranded bound suture of coated braided polyester were compared in the Pennington modi ed Kessler con guration to evaluate the in uence of three concomitantly passing suture strands and their spatial

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arrangement on the biomechanical properties of the repair in static tensile testing. Compared to the 2-strand Pennington modi ed Kessler repair the strength of the intact repair increased in both of these 6-strand repairs. e repair performed with the triple-stranded bound suture reached signi cantly higher yield force, gap forces, and ultimate force compared to the triple-stranded suture, and the yield force exceeded the estimated forces of active mobilization. e biomechanical improvements were considered to be a consequence of the enhanced holding capacity of the locking loops due to the increased tendon-suture interface provided by the broader at structure of the triple-stranded bound suture.

To evaluate the suitability of the bioabsorbable PLDLA 96/4 suture for exor tendon repair compared to the widely used coated braided polyester (Ticron®) suture, the biomechanical material and knot properties were investigated in static tensile testing. In PLDLA suture the sti ness of both unknotted and knotted strands was higher than in polyester suture, though the yield point occurred earlier and the strain at the ultimate point was higher. A secure knot was reached already with two or three throws, while polyester suture required at least ve throws to prevent slippage. e analysis of the cross-sectional area of the knots demonstrated that the secure PLDLA suture knots were signi cantly smaller compared to the polyester knots. us, compared to the coated braided polyester suture the biomechanical and knot properties of the bioabsorbable PLDLA 96/4 suture were found better with loads subjected to the tendon repair during rehabilitation.

A new bioabsorbable PLDLA 96/4 triple-stranded bound suture was investigated biomechanically with static and cyclic tensile testing in the Pennington modi ed Kessler repair. In static testing the yield force, gap forces, and ultimate force improved compared to the repair performed with coated braided polyester triple-stranded bound suture. In cyclic testing PLDLA repair withstood signi cantly more Newton-cycles at every gap point compared to the 6-strand Savage repair which has previously been developed for active mobilization and has successfully been used clinically with active rehabilitation. According to the present results, the Pennington modi ed Kessler repair performed with PLDLA triple-stranded bound suture is strong enough to withstand the forces of early active mobilization.

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LIST OF ORIGINAL PUBLICATIONS

e present study is based on the following articles:

I Viinikainen A, Göransson H, Huovinen K, Kellomäki M, Rokkanen P. A comparative analysis of the biomechanical behaviour of ve exor tendon core sutures. J Hand Surg 2004;29B:536-543.

II Viinikainen A, Göransson H, Huovinen K, Kellomäki M, Törmälä P, Rokkanen P. Material and knot properties of braided polyester (Ticron®) and bioabsorbable poly-L/D-lactide (PLDLA) 96/4 sutures. J Mater Sci Mater Med 2006;17:169-177.

III Viinikainen A, Göransson H, Huovinen K, Kellomäki M, Törmälä P, Rokkanen P. e strength of the 6-strand modi ed Kessler repair performed with triple-stranded or triple-stranded bound suture in a porcine extensor tendon model. An ex vivo study. J Hand Surg 2007;32A:510-517.

IV Viinikainen A, Göransson H, Huovinen K, Kellomäki M, Törmälä P, Rokkanen P. Bioabsorbable poly-L/D-lactide (PLDLA) 96/4 triple-stranded bound suture in the modi ed Kessler repair. An ex vivo static and cyclic tensile testing study in a porcine extensor tendon model. Submitted.

e above articles will be referred to in the text by their Roman numerals.

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ABBREVIATIONS

DIP distal interphalangeal FDS exor digitorum super cialis FDP exor digitorum profundus FPL exor pollicis longusFFL rst linear forceFU ultimate forceFY yield forceKHC knot holding capacityMP metacarpophalangealN NewtonPIP proximal interphalangealPLA polylactic acidPLDLA poly-L/D-lactic acidPLLA poly-L-lactic acidSFL strain at rst linear pointSKHC strain at knot holding capacitySU strain at ultimate point SY strain at yield pointStif sti ness

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INTRODUCTION

In the early years of medicine the tendon was not recognized as a distinct structure. Hippocrates (460-356 BC) together with his contemporary physicians regarded the tendon as a nerve fearing the consequences of suturing. In the literature Avicenna (980-1037 AD), the Muslim physican-philosopher, is usually described as the rst to advocate tendon repair. However, already Galen (129-201 AD), as a physician to the gladiators, is known to have performed tendon repair. In the 16th century the work of the Flemish anatomist, Vesalius (1513-1564), spread the anatomical knowledge of the hand and exor tendons. Although some surgeons in Europe are known to have attempted tendon repair at the time, the fear of catastrophic response to suture remained, and together with problems due to poor asepsis and lack of instruments and suture materials, prevented tendon surgery until the anatomic nature of the tendon was nally experimentally demonstrated by von Haller in 1752 (Chamay 1997, Manske 2005).

In 1918 Sterling Bunnell described in detail the concept and conditions of primary exor tendon repair a er tendon laceration and also advocated protected mobilization to prevent adhesion formation (Bunnell 1918). Faced with poor results due to adhesions he, however, came to another conclusion and suggested not to perform primary repair within the tendon sheath for which he introduced the term “no-man´s land” in 1934 (Bunnell 1948, Manske 2005). Hence, the predominant opinion during the rst half of the 20th century was that secondary tendon repair with gra ing, instead of primary repair in “no man´s land”, should be performed. In 1960 Verdan reported his technique on primary exor tendon repair in “no-man´s land” regarding it as a valid operation. However, it was only a er Kleinert et al. (1967) presented their ten-year experience of primary exor tendon repair with superior results that, despite a great deal of initial disbelief and critisism, it gradually became the treatment of choice.

Since then, both experimental studies on exor tendon injury, repair, and healing as well as clinical investigations have expanded the knowledge and in uenced the treatment of exor tendon injuries (Strickland 2005). However, the problem of restoring normal tendon gliding and hand function a er tendon laceration and primary end-to-end repair within the tendon sheath has not been overcome. e formation of restrictive adhesions between the exor tendons and the tendon sheath still is the major factor impairing functional recovery (Bunnell 1918, Kessler and Nissim 1969, Seradge 1983, Tang 2005).

Compared to immobilization, early controlled passive or dynamic rehabilitation has improved the results a er exor tendon repair by decreasing adhesion formation, increasing repair strength, and improving the functional outcome (Kleinert et al. 1967, Kessler and Nissim 1969, Lister et al. 1977, Strickland and Glogovac 1980, Gelberman et al. 1982, 1983). Later clinical investigations have shown that controlled active mobilization further improves the functional outcome a er exor tendon repair and is at the moment the most valid method to diminish formation of restrictive adhesions (Cullen et al. 1989, Savage and Risitano 1989, Small et al. 1989, Bainbridge et al. 1994, Elliot et al. 1994, Silfverskiöld and May 1994, Baktir et al. 1996, Sirotakova and Elliot 2004, Osada et al. 2006). However, active motion poses greater biomechanical demands on the repair technique compared to passive rehabilitation increasing the risk of repair rupture and gap formation (i.e. opening of the repair) if traditional repair techniques are used (Small et al. 1989, Bainbridge et al. 1994, Peck et al. 1998, Sirotakova and Elliot 1999, Sirotakova and Elliot 2004).

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Earlier, primary end-to-end repair of exor tendon laceration was performed with the core suture only (Kirchmayr 1917, Bunnel 1918, Kessler and Nissim 1969, Kessler 1973), or with epitendinous stitches (Verdan 1960). Later the circumferential epitendinous suture was introduced in conjunction with the core suture to “smooth out” the tendon ends to improve gliding (Lister et al. 1977) (Fig. 1). e core suture was considered the only load-bearing component of the repair until the contribution of the epitendinous suture to the repair strength was established (Wade et al. 1986, 1989). Today, the exor tendon repair is considered a composite of the core suture and the peripheral (i.e. epitendinous) suture with each contributing to the strength of the repair (Wade et al. 1986, 1989, Lotz et al. 1998, Merrel et al. 2003, Mishra et al. 2003). Both new core and peripheral suture techniques have been developed to meet the biomechanical needs of early active rehabilitation. Stronger core suture techniques to withstand the forces of active motion have been developed usually by increasing the number of strands across the repair site forming di erent types of multi-strand repairs (Savage 1985, Lim and Tsai 1996, Sandow and MacMahon 1996, Shaieb and Singer 1997, Kubota et al. 1998, Kusano et al. 1999, McLarney et al. 1999, Barrie et al. 2000a, Dinopoulos et al. 2000, Smith and Evans 2001, Tang et al. 2001b, Wang et al. 2003, Cao and Tang 2005). However, multi-strand repairs are technically demanding in clinical settings increasing tendon handling and requiring more surgical time, which limits their clinical use. Despite vigorous investigation in the area of exor tendon repair, developing a simple and yet strong repair technique that allows smooth gliding of the tendon within the tendon sheath has remained a challenge.

Non-absorbable suture materials, such as coated braided polyester, are commonly used in exor tendon repair (Lawrence and Davis 2005). e advantage of bioabsorbable sutures is

gradual absorption from the tissue, but their use has been limited due to lack of su cient tensile strength half-life. e bioabsorbable poly-L/D-lactide (PLDLA) 96/4 has been considered a potential candidate for exor tendon repair with suitable tensile strength half-life and good biocompatibility in the exor tendon in vivo (Kangas et al. 2001, 2006).

e present experimental tensile testing studies ex vivo were planned to develop a novel, strong, and yet simple bioabsorbable technique for exor tendon repair in the hand to meet the biomechanical requirements of early active mobilization.

A B

F . e exor tendon repair composite includes: A. the core suture (the Pennington modi ed Kessler), and B. the peripheral suture (the simple running).

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REVIEW OF THE LITERATURE

. A

1.1. Macroscopic anatomy of the exor tendons and pulley system

e muscle bellies of the nger exors, the exor digitorum profundus (FDP), exor digitorum super cialis (FDS), and exor pollicis longus (FPL), lie in the proximal forearm with the musculotendinous junctions in the distal forearm. All nine exor tendons pass to the hand through the carpal tunnel, the profundus tendons as its deepest contents. A er the distal border of the carpal tunnel the lumbrical muscles originate from the FDP tendons.

In the palm the FDP tendons continue to lie under the FDS tendons. At the mid-level of the proximal phalanx the FDP tendon passes through the bifurcation in the FDS tendon continuing distally to its broad insertion at the proximal volar third of the distal phalanx of the index, middle, ring and little ngers (Fig. 2). e two slips of the FDS tendon reunite dorsally to the FDP tendon at the “chiasma of Camper” named according to its describer, the Dutch anatomist Petrus Camper (1722-1789) (Schmidt et al. 2005). erea er the tendon splits again and inserts to the volar aspect of the proximal and middle thirds of the middle phalanx. e FPL tendon passes in the hand between the adductor pollicis and exor pollicis brevis muscle bellies, enters the tendon sheath at the level of the metacarpophalangeal joint, and inserts to the base of the distal phalanx of the thumb. e tendon sheath is a bro-osseous tunnel encircling the exor tendons within the digits as a double-walled tube consisting of a visceral and a parietal layer (Cohen and Kaplan 1987, Doyle 1989). In the index, middle, ring, and little ngers the exor sheath includes ve thick annular pulleys (A1-A5) and three cruciate pulleys (C1-C3) and in the thumb two annular pulleys and an oblique pulley (Fig. 3). Distally the tendon sheath runs to the insertion of the FDP tendons and the FPL tendon.

Verdan divided the wrist and the hand into ve zones where the exor tendons pass in anatomically di erent environments (Kleinert and Verdan 1983) (Fig. 3). Zone II, the area of the bro-osseous tunnel also known as “no-man´s land” (Bunnel 1948), creates the greatest challenge for successful surgical treatment and healing of exor tendon injuries.

F . FDS and FDP tendons within the tendon sheath. At the mid-level of the proximal phalanx the FDP tendon passes through the bifurcation in the FDS tendon continuing distally to its insertion at the base of the distal phalanx. e two slips of the FDS tendon reunite forming the “chiasma of Camper”, a er which the tendon splits again and inserts into the middle phalanx.

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1.2. Histology and biochemical composition

e epitenon surrounding the exor tendon is in continuity with the endotenon which divides the tendon into fascicles (Elliot 1965, Goodman and Coueka 2005, James et al. 2008) (Fig. 4).

e epitenon and endotenon consist of well-oriented collagen bres in a criss-cross pattern, cells, blood vessels, lymphatics, and nerves. e tendon fascicles are composed of parallel collagen brils aligned along the axis of the tendon, occasionally separated into groups of

brils by broblasts. e brils are formed of sub brils which consist of micro brils that include ve cross-linked collagen molecules. Collagen constitutes 70-80% of dry-weight of human tendons. In the normal tendon approximately 95% of the collagen is of type I, the principal tensile-resistant bre, and less than 5% is type III, which is seen in the endotenon surrounding type I bres, in extensible structures as the tendon sheath, and during tendon healing (Duance et al. 1977, Amiel et al. 1984). e water content of normal human tendon is 65-75%, most of the water being associated with the extracellular matrix proteoglycans (Elliot 1965, James et al. 2008). In addition to collagen and proteoglycans, other major components of the extracellular matrix in the tendon include elastin and bronectin.

Fibroblasts represent the majority of tendon cells and are divided into subpopulations. e synovial cells line the tendon in the epitenon (Cohen and Kaplan 1987, Banes et al. 1988). e internal tendon cells are tenoblasts with ovoid nuclei and tenocytes with elongated nuclei (Ishii and Umeda 1987). e perivascular cells seen along the adventitia of blood vessels within the epi- and endotenon are immature mesenchymal cells having potential for proliferation and being the source of tenoblasts that invade the area of tendon injury during healing (Gelberman et al. 1983, Ishii and Umeda 1987). In the exor tendons there are also brocartilaginous areas where chondrocyte-like rounded and grouped cells are seen (Lundborg and Myrhage 1977). Also macrophages are present in the normal epitenon and synovial sheath (Khan et al. 1996).

F . e hand divided into Verdan´s zones. e pulley system of the ngers II-V and the pulley system of the thumb. e annular pulleys prevent bowstringing of the tendons, while the cruciate pulleys adjust the tendon sheath during nger exion.

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e regions subjected to di erential mechanical load also show di erences in the extracellular matrix composition (Merrilees and Flint 1980, Okuda et al. 1987, Soejima et al. 2003). e dorsal side subjected mainly to distortional strain and tension is more elastic and stronger against tensile forces with higher rates of collagen synthesis, dense collagen brils, and lower proteoglycan content. e volar side glides over the pulley system and is also subjected to compressive forces with an increased amount of proteoglycans increasing the water content, and thinner collagen brils.

1.3. Vasculature and nutrition

In the distal forearm and palm region the exor tendons are surrounded by the highly vascularised paratenon (Manske and Lesker 1985). e segmental blood vessels of the paratenon penetrate the tendon and travel longitudinally between the bundles.

Within the tendon sheath the exor tendons have three distinct main sources of blood supply 1) the intrinsic longitudinal vessels rising from the palm, 2) vinculae, and 3) the osseotendinous junction (Lundborg et al. 1977). Both the super cialis and profundus tendon have areas of low vascularity palmarly between the A2 and A4 pulleys which is considered to relate to the mechanical forces acting on the tendon from the pulleys and joints (Harrison et al. 2003).

Radioactive tracer studies have compared the role of di usion and perfusion in the rabbit, chicken, dog, and monkey exor tendons and shown that all segments of the tendon receive nutrition both via di usion and perfusion, with di usion being the major nutrient pathway in all segments within the tendon sheath (Manske et al. 1978, Lundborg et al. 1980, Manske and Lesker 1982). Studies determining the viability and healing potential of tendon segments nourished only through synovial di usion (Lundborg and Rank 1980) and the viability of tendon segments in vitro (Manske and Lesker 1984, Manske et al. 1985) further con rmed the role of di usion as the major nutritional pathway in the exor tendons.

F . Schematic drawing of the tendon structure.

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. B

2.1. Tendon strength

e tension bearing capability of tendons is primarily due to the mechanical properties of collagen (Goodman and Choueka 2005). e mean sti ness of human FDP tendon has been reported as 35.9 N/mm (Lotz et al. 1998). e mean breaking strength of FDP tendon to bone insertion has been reported as 560 N and the FDP tendon strength as 620-1180 N with the mean elongation of 10.7-12.9% at rupture (Pring et al. 1985).

2.2. Forces during nger exion

Flexor tendon forces have been investigated in healthy tendons at the wrist level during carpal tunnel release (Urbaniak et al. 1975, Schuind et al. 1992, Kursa et al. 2006). Urbaniak et al. (1975) reported the mean force of 2 N in the FDP during passive exion-extension and 9 N during active exion against slight resistance.

Schuind et al. (1992) measured higher forces during active exion reporting the mean force of 19 N (range 1-29 N) in the FDP during unresisted DIP exion and 25 N (range 4-35 N) in the FPL during unresisted interphalangeal exion. Tip pinch represented strong resisted active

exion, and the mean force of 26 N (range 8-59 N) and 83 N (20-118 N) were measured in the FPL and FDP, respectively.

Kursa et al. (2006) investigated forces during active unresisted nger exion and nger extension with the wrist either in the neutral position or in 30° exion and with di erent metacarpophalangeal (MP) joint angles. In the FDP the mean forces between 1.3 N ±0.9 N and 4.0 N ± 2.9 N and in the FDS between 1.3 ± 0.5 N and 8.5 N ± 10.7 N were measured depending on the wrist and MP joint positions. Unexpectedly, the tendon forces were similar during active nger exion and extension. Increasing the MP joint angle enhanced the force in both the FDP and FDS during active extension and exion. e FDS forces were also increased with the exed wrist position, while the wrist position did not in uence the FDP forces. A higher mean maximum FDP force was recorded when the ngers were held in the static exed position (holding exercises) than during a dynamic extension- exion movement.

2.3. Tendon excursion

e distance of the exor tendon from the axis of the rotation of the joint is determined by the annular pulleys which keep the exor tendons along the volar surface of the phalanges and joint capsules, preventing bowstringing during exion. Factors that increase the distance of the tendon from the axis of the joint, such as pulley resection or an increase in the perpendicular distance of the pulley from the longitudinal axis of the bone, will increase the required tendon excursion to produce joint rotation (Goodman and Choueka 2005, Strickland 2005). e A2 and A4 pulleys, which are the tightest and largest, are considered the most important in preventing bowstringing and loss of joint motion. e cruciate pulleys and the oblique pulley of the thumb adjust the sheath during nger exion by allowing the annular pulleys to approximate each other.

Several studies have de ned exor tendon excursion in the hand (Verdan 1976, McGrouther et al. 1981, Wehbé and Hunter 1985a, 1985b). e maximal amplitude of the gliding of the FDP

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is 5 mm at the DIP -level, 17 mm at the PIP -level, 23 mm at the MP -level, 38 mm in the carpal tunnel, and 83 mm in the distal forearm. For the FDS the amplitude is 16 mm at the PIP, 26 mm at the MP, 46 mm in the carpal tunnel, and 88 mm in the distal forearm (Verdan 1976). McGrouther and Ahmed (1981) reported from human cadavers that, when measured within zone II, the relation between the DIP exion and FDP excursion as well as between the PIP exion and FDS excursion was linear with an average of 1.0 mm of FDP excursion per 10 degrees of DIP exion, and of 1.3 mm of both FDS and FDP excursion per the 10 degrees of the PIP exion. A pure MP-joint motion produced no excursion in the FDP and FDS tendons. Hence, the DIP exion was the only factor moving the FDP relative to the FDS. e excursion of the FDP and FDS in di erent wrist positions has been studied by Wehbé and Hunter (1985a, 1985b) in vivo during carpal tunnel release. With the wrist in the neutral position the mean excursion of the FDS, FDP, and FPL tendons was 24 mm, 32 mm, and 27 mm, respectively. With concomitant active wrist and nger extension and wrist and nger exion the amplitude of the excursion of the exor tendons increased to 49 mm for the FDS, to 50 mm for the FDP, and to 35 mm for the FPL (Wehbé and Hunter 1985a). e FDS tendon achieved its maximum gliding in respect to the exor tendon sheath and bone (28 mm) with the straight-

st position (MP and PIP joints in exion; DIP joints in extension). e FDP tendon achieved its maximum gliding in respect to sheath and bone (34 mm) with the st position (MP, PIP, and DIP joints in exion). Maximum gliding between the two exor tendons (11 mm) was achieved with the hook position (MP joints in extension; PIP and DIP joints in exion) (Wehbé and Hunter 1985b).

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3.1. Biomechanical testing methods

Several testing methods have been used to investigate the biomechanical properties of exor tendon repair techniques. Lack of uniformity among testing protocols has resulted in widely ranging results making the comparison di cult (Goodman and Choueka 2005).

e most commonly used biomechanical testing method for exor tendon repair techniques is static linear tensile testing ex vivo (i.e. outside an organism). e repaired tendon is subjected to a single linear load-to-failure pull and the produced load-deformation curve is analysed (Goodman and Choueka 2005). Earlier studies commonly analysed the ultimate force to evaluate the strength of the repair, though at ultimate force a gap o en already exists at the repair. erefore, increasing emphasis has been put on analysing gap forces and the linear region of the load-deformation curve (Lotz et al. 1998, Dinopoulos et al. 2000). e load-deformation curve has three regions: An initial non-linear region followed by a linear region with constant elongation for a given load, and the failure region. e sti ness (N/mm) of the repair is de ned as the slope of the linear region, re ecting the ability of the tendon repair to resist deformation during loading. e linear region ends at the yield point; therea er the curve is reduced, but the force o en continues to increase until the ultimate point.

Static linear tensile testing does not correspond to physiologic loading, because it does not allow evaluation of the in uence of repetitive physiological loading on the tendon repair, angular pull on repair strength, bulk of repair on the gliding resistance of the tendon within the sheath or work of exion (Pruitt et al. 1991, Aoki et al. 1995b, Tang et al. 2001a, Zhao et al. 2001b). It allows investigating large numbers of tendons with direct visualisation of the

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repair site to record gap formation during testing, thus o ering a tool to compare the strength and mode of failure of di erent repair techniques minimizing other variables a ecting repair strength (Goodman and Choueka 2005).

Linear dynamic testing o ers a tool to evaluate the in uence of repetitive loading on the strength of the tendon repair providing a more physiologic assessment of the e ects of postoperative active motion (Pruitt et al. 1991, Sanders et al. 1997, Barrie et al. 2000a, Barrie et al. 2001, Wolfe et al. 2007). In dynamic testing the tendon repair is cyclically loaded. Dynamic loading has been shown to initiate gap formation at signi cantly lower loads compared to static testing (Pruitt et al. 1991, Sanders et al. 1997). Testing protocols that include dynamic testing followed by load to failure testing (Choueka et al. 2000, Mishra et al. 2003) investigate the residual strength of the repair a er a known number of cycles simulating the clinical situation of higher load subjected to the repair during the rehabilitation period.

In physiological conditions the tendon repair is also subjected to angular pull. Curvilinear tensile testing models where the tendon is pulled over an arti cial pulley have been used to evaluate the in uence of the tension direction on the tendon repair strength (Tang et al. 2001a, Cao et al. 2002, Tang et al. 2003b). Angular pull initiates gap formation at lower loads compared to linear decreasing repair strength in proportion to the angle of pull.

e in situ models test the exor tendon repair in its anatomical place within the tendon sheath in cadaveric hands. Both static load-to-failure (Komanduri et al. 1996) and cyclic (Choueka et al. 2000, Alavanja et al. 2005) tests have been performed. In situ testing simulates the forces subjected to the tendon during nger exion including tension on the dorsal surface, compression on the palmar surface, and frictional forces within the sheath.

e ability of the exor tendon to glide following repair has been evaluated by di erent methods measuring either the gliding resistance or work of exion (Lane et al. 1976, Aoki et al. 1995a, 1995b, Halikis et al. 1997, Zhao et al. 2001b, 2002b, Tanaka et al. 2003). e gliding resistance is measured by pulling the tendon under a pulley or through the tendon sheath. e test measures only the friction force at the tendon–pulley interface and allows the precise measurement of surface interactions but is not able to assess overall nger function or the e ect of adhesion formation a er tendon repair (Tanaka et al. 2003). e work of exion measurement performed in situ a er in vivo repair and healing characterizes the whole nger function during exion and is in uenced both by factors a ecting tendon gliding or inhibitors to joint motion (Tanaka et al. 2003). e total work of exion quantitatively represents the sum of all forces that resist digit exion during tendon gliding and is composed of internal and external resistance. e internal work of exion is a combination of the surface friction between the tendon and the exor sheath, the bulk e ect due to t of the tendon within the

exor sheath, and the resistance resulting from adhesions. e external resistance includes joint sti ness, so tissue resistance, the mass of digit, and the resistance of antagonist muscles.

e total work of exion does not correlate with the gliding resistance; thus, it is not able to assess the surface characteristics of the repair techniques just as the gliding resistance is not able to assess the total nger function (Tanaka et al. 2003). e internal work of exion and the gliding resistance correlate strongly, but they are not equal due to the in uence of adhesions on the former.

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3.2. Properties of the tendon repair

Strickland (2000) has outlined six characteristics that exor tendon repair should satisfy prior to clinical application: Easy placement of sutures in the tendon, secure suture knots, smooth junction of tendon ends, minimal gap formation at the repair site, minimal interference with tendon vascularity, and su cient strength throughout healing to permit the application of early motion stress to the tendon.

e forces subjected to the tendon repair (Chapter 2.2.) depend on the rehabilitation technique used, i.e. immobilization, or passive, dynamic, or active mobilization. e actual strength of a repair needed to withstand motion is not exactly known, but it has been estimated to be 50% higher (Strickland 1999) than the measured forces in healthy tendons due to postoperative factors increasing tendon gliding resistance and work of exion. According to this and the in vivo forces measured by Schuind et al. (1992), the exor tendon repair should withstand the mean forces of 29 N, but even up to 53 N due to the wide variation in the forces between individuals during active unresisted exion exercises. In addition, postoperative tenomalacia at the suture-tendon junction may decrease initial repair strength (McDowell et al. 2002). With immobilization the strength of the tendon repair has been shown to decrease signi cantly initially (Urbaniak et al. 1975, Hitchcock et al. 1987). However, early passive (Gelberman et al. 1982, Hatanaka et al. 2000, Boyer et al. 2001a) and especially early active motion (Hitchcock et al. 1987, Aoki et al. 1997, Wada et al. 2001a, 2001b) have been shown to prevent the initial loss of tensile strength.

e initial strength of the tendon repair depends on the material properties and knot security of the sutures as well as on the holding capacity of the suture grips of the tendon. e biomechanical properties of the suture depend on the material and can be improved by increasing the number of strands crossing the repair site (Savage 1985) and the suture calibre (Barrie et al. 2001, Taras et al. 2001). e holding capacity of the repair of the tendon has been shown to be dependent on the con guration (Savage 1985, Hotokezaka and Manske 1997, Wada et al. 2000, Barrie et al. 2001, Xie and Tang 2005), size (Hatanaka and Manske 1999, Xie et al. 2005), and number (Kubota et al. 1996a) of the grips.

e exor tendon repair can be regarded as a composite of the core and the peripheral sutures (Fig. 1) (Lotz et al. 1998, Merrel et al. 2003) with both contributing to the repair strength. Failure of the peripheral suture has been shown to precede core suture failure (Wade et al. 1986, 1989, Diao et al 1996, Lotz et al. 1998, Barrie et al. 2000a, Momose et al. 2001, Merrel et al. 2003, Mishra et al. 2003). By using an analytic model Lotz et al. (1998) showed that in a repair composite of the 2-strand modi ed Kessler 4-0 core suture and simple running 6-0 peripheral suture, the applied load was carried from 64% to 77% by the peripheral suture at its point of rupture. A er failure of the peripheral suture the total force is transferred onto the core suture. If the strength of the core suture strands exceeds the subjected force, the repair may still continue to increase in strength with concomitantly increasing gap formation (Lotz et al. 1998, Barrie et al. 2001). Ultimate failure nally occurs either by suture pullout or by suture breakage, if the holding capacity of the suture grips of the tendon exceeds the material strength (Barrie et al. 2001, Taras et al. 2001, Lawrence and Davis 2005, Miller et al. 2007).

According to Lotz et al. (1998), the ultimate strength of the core suture is actually irrelevant to the overall strength of the repair composite because of the sti ness imbalance between the core and the peripheral suture leading to overloading and rupture of the weaker peripheral suture. Hence, the sti ness and strength of the core and peripheral suture should be modi ed

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to achieve their ultimate strength simultaneously. is could be achieved by increasing the sti ness of the core suture rather than its ultimate force. An alternate approach is to adjust the strain at the yield point of the peripheral suture to equal the strain at the yield point of the core suture. e latter was the aim of Merrel et al. (2003) who increased the purchase of the simple running peripheral suture and reached improved ultimate strength and gap resistance.

e importance of optimizing load sharing between the core and the peripheral suture is also supported by the results of Mishra et al. (2003) who compared nylon and coated braided polyester sutures in the modi ed Kessler repair with polypropylene simple running peripheral suture. With the more elastic nylon as core suture material, gap formation was increased and failure occurred earlier.

3.3. Core suture

3.3.1. Number of strands

Most of the earlier exor tendon core sutures were 2-strand techniques: the Kirchmayr (Kirchmayr 1917) (Fig. 5A), Bunnell criss-cross (Bunnell 1918), Mason and Allen (Mason and Allen 1941), Kessler (Kessler and Nissim 1969) (Fig. 5B), and Tsuge repair (Tsuge et al. 1975) (Fig. 7A). A modi cation of the original Kichmayr repair with the knot placed between the tendon ends, generally known as the modi ed Kessler repair (Fig. 5C, D), is the most commonly used and investigated 2-strand repair technique both experimentally (Table 1) and clinically. e same repair performed with two knots is called the Tajima repair (Tajima et al. 1984) (Fig. 5E). e strength of the locking con guration of the modi ed Kessler repair (Pennington 1979) (also called as the Pennington modi ed Kessler or Pennington repair) (Fig. 5D) reported in the static linear tensile testing studies (Table 1) is strong enough to withstand the forces of passive, but not active, rehabilitation, clinically seen as increased rupture rates (Small et al. 1989, Bainbridge et al. 1994, Peck et al. 1998, Sirotakova and Elliot 1999). e modi ed Pennington con guration (Fig. 5F), with the longitudinal strands taken out dorsally to ensure that a locking con guration is formed, has been introduced by Hatanaka and Manske (1999, 2000) to increase repair strength (Table 1).

F . e evolution of A. the original Kirchmayr repair (Kirchmayr 1917) to B. Kessler repair (Kessler and Nissim 1969), C. grasping modi ed Kessler repair (Pennington 1979), D. Pennington modi ed Kessler repair (also called as locking modi ed Kessler and Pennington repair) (Pennington 1979), E. Tajima repair (Tajima 1984), and F. modi ed Pennington repair (Hatanaka and Manske 1999).

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e rst multi-strand repair was introduced by Savage (1985) who incorporated six suture strands across the repair site and three double cross-stitch grasps in both tendon ends (Fig. 6F) to increase repair strength and demonstrated improved gap resistance and ultimate force correlating linearly with the number of strands. e 6-strand Savage achieved su cient strength to withstand the estimated forces of early active mobilization (Savage 1985) (Table1). Since then, several investigators have developed and investigated multi-strand techniques that consist of multiple separate core sutures performed with single-stranded suture; thus, the number of separate suture grips of the tendon is increased concomitantly. Four-strand techniques including the double modi ed Kessler (Fig. 6A), cruciate locked and non-locked (Fig. 6B), cruciate cross-stitch locked (Fig. 6C), Savage (Fig. 6D), modi ed Becker (Fig. 6E), Strickland, and Robertson repairs (Robertson and Al-Qattan 1992, Noguchi et al. 1993, Greenwald et al. 1994, Aoki et al. 1995c, Shaieb and Singer 1997, Kubota et al. 1998, Zatiti et al. 1998, McLarney et al. 1999, Barrie et al. 2000b, Wada et al. 2000, Slade et al. 2001, Smith and Evans 2001, Angeles et al. 2002, Lawrence and Davis 2005, Miller et al. 2007), and 6-strand techniques including the Savage (Fig. 6F), modi ed Savage (Fig. 6G), and modi ed triple Kessler (Fig. 6H) repairs (Aoki et al. 1994, 1995c, Sandow and MacMahon 1996, Shaieb and Singer 1997, Gordon et al. 1998, Zatiti et al. 1998, Gordon et al. 1999, Barrie et al. 2000b, Slade et al. 2001) have demonstrated improved biomechanical properties compared to 2-strand techniques in static tensile testing ex vivo (Table 1). Also in cyclic testing multi-strand techniques have reached signi cantly improved gap resistance and fatigue strength compared to 2-strand repairs (Sanders et al. 1997, Choueka et al. 2000, Barrie et al. 2001). However, most of these studies have compared suture techniques with multiple variables, e.g. the number of strands, di erent con guration, suture material or suture calibre, at the same time.

e e ect of increasing the number of strands by performing multiple similar but separate core sutures has been less investigated. e 4- and 6-strand modi ed Kessler repairs reached signi cantly higher sti ness, gap forces, and ultimate force compared to the 2-strand repair

F . Multi-strand core suture techniques performed with single-stranded suture. A. Double modi ed locking Kessler (Shaieb and Singer 1997), B. Cruciate non-locked (McLarney et al. 1999), C. Cruciate cross-stitch locked (Barrie et al. 2000b) D. 4-strand Savage (Noguchi et al. 1993), E. Augmented Becker (also called as MGH repair) (Greenwald et al. 1994), F. 6-strand Savage (Savage 1985), G. Modi ed Savage (Sandow and MacMahon 1996), H. Triple modi ed Kessler (Shaieb and Singer 1997).

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(Shaieb and Singer 1997, Kubota et al. 1998, Slade et al. 2001, Smith and Evans 2001) (Table 1). Also when comparing the 2-, 4-, and 6-strand Savage (Aoki et al. 1995c) and the 2-strand Tsuge, double loop, and triple loop repairs (Kusano et al. 1999, Labana et al. 2001) (Fig. 7B-D) the gap forces and the ultimate force increased along with the number of strands (Table 1).

More recently double-stranded sutures (i.e. loop or looped suture) have been used in performing multi-strand repairs (Lee 1990, Tang et al. 1994, Lim and Tsai 1996, Winters et al. 1998, Kusano et al. 1999, Barrie et al. 2000a, Dinopoulos et al. 2000, Boyer et al. 2001a, Labana et al. 2001, Tang et al. 2001b, Xie et al. 2002, Wang et al. 2003, Tanaka et al. 2004, Cao and Tang 2005) (Fig. 7C-J). In several studies multi-strand modi cations of the Tsuge repair (Fig. 7B-G) have been investigated, and improved repair gap and ultimate force values along with the number of strands have been reported (Lim and Tsai 1996, Kusano et al. 1999, Labana et al. 2001, Tang et al. 2001b, Cao et al. 2002, Xie et al. 2002, Wang et al. 2003, Cao and Tang 2005) (Table 1). Dinopoulos et al. (2000) investigated the 4- and 8-strand modi ed grasping Kessler repairs (Fig. 7I, J) with static tensile testing and reported that increasing the number of strands improved only the resistance to initial gap formation, but a er a gap of 3 mm or larger had been formed both repairs were equally susceptible to rupture.

Among of the studies investigating repair techniques performed with double-stranded suture only the study by Barrie et al. (2000a) evaluated the increasing of the number of strands within the same con guration using either single- or double-stranded suture. ey investigated cruciate non-locked (Fig. 6B) and cruciate cross-stitch locked (Fig. 6C) con gurations as 4- and 8-strand repairs with cyclic tensile testing ex vivo. Although the material strength

F . Core suture techniques performed with double-stranded suture. A. Original Tsuge (Tsuge et al. 1975), B. Tsuge (Tsuge et al. 1977), C. Double loop suture (Tang et al. 1994), D. Triple loop suture (Tang et al. 1994), E. Lim (Lim and Tsai 1996), F. 4-strand modi ed Tang (Cao and Tang 2005), G. Modi ed Tang (Wang et al. 2003), H. Yoshizu (Kusano et al. 1999), I. 4-strand modi ed Kessler (Dinopoulos et al. 2000), J. 8-strand modi ed Kessler (Dinopoulos et al. 2000).

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increased, the results were controversial in regard to the repair holding capacity, because no di erence was seen in the gap resistance, though the fatigue strength improved.

Several investigators have also reported progressively improving biomechanical properties along with the increasing number of core suture strands during in vivo healing with follow-ups of up to six weeks (Aoki et al. 1997, Winters et al. 1998, Kusano et al. 1999, Boyer et al. 2001a).

3.3.2. Loop con guration

3.3.2.1. Locking versus grasping loop

Pennington (1979) was the rst to describe precisely the relation of the longitudinal and transverse intratendinous parts in the modi ed Kessler repair (Fig. 5C, D). When the transverse component of the suture passes volar to the longitudinal strand (Fig. 5D), it locks onto the

bres it encompasses (Fig. 8). Failure of the locking loop occurs either by cutting the bres within the loop or by unwinding and bending the bres within the loop, while the grasping loop does not tighten around the tendon but collapses and pulls out (Hotokezaka and Manske 1997) (Fig. 8).

Several experimental ex vivo studies have demonstrated the biomechanical advantages of locking loops over grasping loops in exor tendon repair (Hotokezaka and Manske 1997, Barrie et al 2000a, Hatanaka and Manske 2000, Wada et al. 2000). Hotokezaka and Manske (1997) rst showed in a linear testing model with a 2-strand core suture model that locking loops reached signi cantly higher ultimate force and reduced distraction compared to grasping loops (Table 1). e biomechanical advantages of the locking loops compared to grasping loops are obtained only with 3-0 or heavier core suture (Hatanaka and Manske 2000, Taras et al. 2001) (Table 1). If the material strength of the suture is inferior to the holding capacity of the suture grips of the tendon, failure occurs by suture rupture before the true biomechanical properties of the suture loops are obtained. Wada et al. (2000) investigated the locking and grasping con gurations of the 4-strand modi ed Kessler and 4-strand cruciate techniques performed with 3-0 suture and reported that grasping con gurations failed by suture pullout,

F . Schematic drawing of the grasping and locking loops. In the grasping loop, the loop opens when tension is applied to the suture ends. In the locking loop the suture tightens around the tendon

bres when loaded.

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while locking con gurations failed by suture breakage at the knot or at the locking loop with signi cantly higher loads (Table 1). e locking con gurations also reached signi cantly higher 2 mm gap strength, but the sti ness values did not di er. In a cyclic tensile test comparing non-locked and locked 4-strand and 8-strand techniques, the locked repairs demonstrated signi cantly improved resistance to 1 and 2 mm gap formation (Barrie et al. 2000a).

Also in vivo in canine exor tendon repair with locking and grasping modi ed Kessler repairs and passive mobilization, the locking repairs demonstrated higher tensile strength and gap strength at 0, 3, and 21 days from the operation (Hatanaka et al. 2000).

3.3.2.2. Type and size of locking loop

Locking con gurations di er in the tendon-suture interface and can be categorized into two groups: circle-locking and cross-locking (Xie and Tang 2005). e repairs containing circle-locking loops are the modi ed locking Kessler (Fig. 5D) (i.e. the Pennington modi ed Kessler repair) (Pennington 1979), circle-loop models of Xie and Tang (2005), and the loops located in the Tsuge repair (Fig. 7B) (Tsuge et al. 1977) and its multi-strand modi cations, the double and triple loop repairs (Fig. 7C, D) (Tang et al. 1994, Tang et al. 2001b), modi ed Tang repairs (Fig. 7F, G) (Wang et al. 2003, Cao and Tang 2005), and Lim repair (Fig. 7E) (Lim and Tsai 1996). e repairs containing cross-locks are the Becker (Becker and Davido 1977), augmented Becker (Fig. 6E) (Greenwald et al. 1994), Savage (Fig. 6F) (Savage 1985), modi ed Savage (Fig. 6G) (Sandow and McMahon 1996, Xie et al. 2002), and cruciate cross-stitch locked (Fig. 6C) (Barrie et al. 2000a, 2000b, 2001) techniques. e cross-locks are further divided into exposed and embedded, which both are present e.g. in the Savage technique (Fig. 6F). In the study of Xie and Tang (2005) the circle-locking loops and either exposed or embedded cross-locks did not di er signi cantly in regard to the initial gap force, 2-mm gap force or ultimate force (Table 1).

When developing his 6-strand repair technique, Savage (1985) demonstrated that the strength depended on what he called the “grasp” con guration and was increased with two repeated cross-locks (one embedded and one exposed). In the modi ed Kessler type of loop increasing the number of locking loops per suture strand from one to two has not been shown to in uence the biomechanical properties, while increasing the number of grasping loops from one to two improved the strength (Hotokezaka and Manske 1997)(Table 1).

Increasing the cross-sectional area of the tendon incorporated into each locking loop from 5% up to 15% in the modi ed Pennington technique (Fig. 5F) has been shown to increase the ultimate force. Further increase up to 25% or overlapping the locking loops did not improve the ultimate force signi cantly, while the tendency of gap formation increased (Hatanaka and Manske 1999) (Table 1). Dona et al. (2004) investigated the 4-strand cruciate repair with each locking loop comprising 10%, 25%, 33% or 50% of the tendon width and reported that the locking loops of 25% reached the highest 2 mm gap force, ultimate force, and sti ness (Table 1). Xie et al. (2005) reported that in 2- and 4-strand repair models locking circles with a diameter of 2 or 3 mm reached a signi cantly higher gap and ultimate force than those with a diametre of 1 mm. e biomechanical properties of the 2 and 3 mm diameter locking circles did not di er signi cantly (Table 1).

Also the direction of the locking loops a ects the strength of the modi ed Kessler repair (Tan and Tang 2004). e ultimate force and 2 mm gap force were signi cantly higher with the locking circles perpendicular to the long axis compared to the locking circles parallel to the long axis of the tendon (Table 1).

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3.3.3. Core suture purchase

e length of the core suture purchase determines the segment of the tendon incorporated into the repair. e ideal ratio of the length of the longitudinal strands to the tendon diameter for various repair techniques is not known, though it is generally assumed that a certain distance from the suture grasping or locking points to the laceration site should be maintained (Tang et al. 2005).

e in uence of the core suture purchase on the biomechanical properties of the tendon repair was rst demonstrated in obliquely cut tendons (Tang et al. 2003a, Tan and Tang 2004) (Table 1). Tang et al. (2003a) demonstrated that lengthening the longitudinal strands signi cantly increased the 2 mm gap force and ultimate force in both grasping and locking modi ed Kessler repairs compared to obliquely and conventionally positioned core sutures. Tan and Tang (2004) showed that both in the locking 2-strand Kessler and 4-strand cruciate repair the gap resistance and ultimate force improved, as the core suture was lengthened and the optimal span in the short side of the tendon was 1.0 cm.

Tang et al. (2005) investigated a 2-strand grasping modi ed Kessler technique and a 4-strand circle-locking technique in transversely cut tendons and reported that the gap resistance and ultimate force enhanced along with the increased suture purchase. ey determined that the optimal range was between 0.7 and 1.0 cm, while the core suture purchase of 0.4 cm or less resulted in signi cantly weaker repairs. Cao et al. (2006) similarly concluded a er investigating the grasping double-modi ed Kessler, locking cruciate, and 4-strand modi ed Savage repairs that the gap resistance and ultimate forces improved in all techniques and the sti ness in the double-modi ed Kessler and modi ed Savage repairs when the core suture length was increased from 0.4 to 1.0 cm (Table 1) and that lengthened core sutures failed by suture rupture, while the shorter core sutures failed primarily by suture pullout suggesting decreased repair holding power of the tendon substance. us, increased core suture purchase was considered to improve the biomechanical properties by establishing a greater tendon-suture interaction (Cao et al. 2006).

3.3.4. Suture calibre

Despite numerous investigations on the tendon repair techniques, only a few have focused on the e ect of the suture calibre on the biomechanical properties of exor tendon repairs. e strength of the 4-0 suture has been reported to be less than the holding capacity of several locking and grasping 2-, 4-, and 6-strand repairs leading to failure predominantly by suture rupture (Barrie et al. 2000a, Choueka et al. 2000, Barrie et al. 2001, Taras et al. 2001, Xie et al. 2002, Dona et al. 2004, Lawrence and Davis 2005, Xie et al. 2005, Cao et al. 2006). Failure with 3-0 suture has been reported due both to suture rupture and pullout (Hatanaka and Manske 1999, 2000, Wada et al. 2000, Barrie et al. 2001, Taras et al. 2001, Mishra et al. 2003, Miller et al. 2007). With the modi ed Pennington (Fig. 5F) and locking double-grasping con gurations failure predominantly by suture rupture has been reported even with 2-0 sutures (Hatanaka and Manske 2000, Taras et al. 2001).

Increasing the suture calibre has been reported to increase the ultimate force in static testing (Mashadi and Amis 1991, Hatanaka and Manske 2000, Taras et al. 2001 Alavanja et al. 2005) and fatigue strength in dynamic testing (Barrie et al. 2001). e in uence of the suture calibre on the gap resistance is not well established. In the 4-strand locked cruciate cross-stitch repair

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(Fig. 6C) increasing the suture calibre from 4-0 to 3-0 and to 2-0 did not improve the gap resistance of the repair in a combination of cyclic and static tensile testing (Alavanja et al. 2005). However, Hatanaka and Manske (2000) reported that 2-0 suture increased the gap strength of the locking loop specimens (modi ed Pennington repair, Fig. 5F) (Table 1).

Although the in uence of the suture calibre on the gap resistance has been controversial, the use of 3-0 suture has been recommended to o er a margin of safety for the repair through increased material strength (Hatanaka and Manske 2000, Barrie et al. 2001, Taras et al. 2001).

3.3.5. Volar versus dorsal placement of sutures

Historically, the volar placement of sutures was advocated to avoid injuring the dorsally raising vasculature of the profundus tendon (Barrie and Wolfe 2001). As di usion from the synovial

uid has been shown to be the major nutrient pathway in all parts of the tendon (Manske et al. 1978, Lundborg et al. 1980, Manske and Lesker 1982), placement of sutures in the dorsal vascular areas of the tendon has also been suggested (Manske 1988).

e results of the biomechanical in uences of dorsal versus palmar suture placement vary. Using linear static tensile testing Soejima et al. (1995) reported that the dorsal placement of the modi ed Kessler repair resulted in signi cantly higher ultimate force compared to volar placement (Table 1). Tested separately, the dorsal half of FDP tendon tissue reached signi cantly higher tensile strength compared to the palmar part, which was considered to contribute to the strength of the suture-tendon interface. However, Stein et al. (1998) who also used a linear model did not nd any di erence between dorsally or volarly placed core sutures. Komanduri et al. (1996) using an in situ testing model found that dorsally placed core sutures reached signi cantly higher breaking strength compared to volar suture placement.

ey considered the di erence to be due to the biomechanics of the joint and pulley system creating palmar compression and dorsal distraction at the repair.

3.3.6. Placement of the knots

e location and number of knots have been shown to in uence the strength of the tendon repair in static tensile testing ex vivo (Savage 1985, Aoki et al. 1995c). Decreasing the number of knots and placing them outside the repair on the tendon surface increases the strength of the repair compared to knots placed between the tendon ends (Aoki et al. 1995c) (Table 1). However, knots on the tendon surface increase the gliding resistance of the repair within the tendon sheath signi cantly (Momose et al. 2000, 2001).

Pruitt et al. (1996) investigated in a canine model in vivo the in uence of placing four knots either between the tendon ends or outside on the tendon surface and found that though the repair strength was initially higher in the knots-outside repairs (Table 1), a er six weeks the knots-inside repairs showed a signi cant increase in tensile strength compared to the knots-outside repairs. e increase in the amount of suture material up to 26% of the tendon cross-sectional area in the knots-inside repairs did not have any deleterious e ects on the tensile strength of the repair during the six-week follow-up.

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3.3.7. Suture materials

e properties of an ideal suture material for exor tendon repair include the following (Trail et al. 1989): High tensile strength; absorbable, but maintaining its tensile properties until tendon repair has achieved adequate strength; minimal tissue response; easily knotted with good knot holding capacity; inextensible to prevent gapping; and easy to use.

3.3.7.1. Biomechanical properties

Earlier stainless steel was used as core suture material in exor tendon repair due to its superior tensile strength and inert tissue properties (Urbaniak et al. 1975), but the material was abandoned because it was poor to handle and kinked while being tied. Recently, a new metal suture, Nitinol (NiTi), has been introduced as a possible new tendon repair material (Moneim et al. 2002, Kujala et al. 2004). NiTi is a shape memory alloy with high strength and sti ness and better handling properties compared to stainless steel.

Non-absorbable synthetic sutures, especially coated braided polyester, monofilament nylon, and monofilament polypropylene are nowadays used in flexor tendon repair (Lawrence and Davis 2005). Coated braided polyester suture is the most commonly used core suture material, though nylon is also often favoured, especially in repairs performed with looped suture (Table 1). Compared to monofilament nylon and polypropylene sutures, coated braided polyester suture demonstrates significantly higher tensile strength and stiffness (Trail et al. 1989, Lawrence and Davis 2005, Vizesi et al. 2008). In addition, the stiffness of both polypropylene and nylon suture has been shown to decrease significantly in the body temperature, while the stiffness of coated braided polyester suture was not affected (Vizesi et al. 2008). In ex vivo flexor tendon repair coated braided polyester suture has been shown to provide better gap resistance compared to monofilament nylon suture which allowed early central gapping of the repair (Mishra et al. 2003) and to increase repair stiffness compared to monofilament polypropylene suture (Lawrence and Davis 2005). The disadvantage of the coated braided polyester suture is the poor knot holding capacity due to coating, as five throws per knot are needed to prevent slippage (Holmlund 1974).

Recently, a braided polyblend polyethylene suture (FiberWire®) has been introduced for flexor tendon repair. In biomechanical material testing of unknotted strands with 4-0 calibre, the polyblend polyethylene suture demonstrated significantly higher ultimate force (37 N) and stiffness (11 N/mm) compared to coated braided polyester (25N, 8.2 N/mm), monofilament nylon (22 N, 2.5 N/mm), and polypropylene sutures (25 N, 5.0 N/mm), and a similar ultimate force but higher stiffness compared to braided stainless steel (36 N, 14.8 N/mm) (Lawrence and Davis 2005, Miller et al. 2007). In the 4-strand cruciate cross-stitch repair (Fig. 6C) the 4-0 polyblend polyethylene and braided stainless steel repairs reached significantly higher stiffness, ultimate force, and initial gap force compared to coated braided polyester and especially nylon and polypropylene repairs (Lawrence and Davis 2005) (Table 1). Braided polyblend polyethylene suture of 3-0 calibre also increased the ultimate force of a locking repair compared to coated braided polyester and nylon, because with the stronger material suture breakage occurred at higher force (Miller et al. 2007). The gap resistance of the repairs performed with polyblend polyethylene and coated braided polyester did not differ significantly, while monofilament nylon repairs demonstrated significantly lower gap resistance (Miller et al. 2007).

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Bioabsorbable suture materials have not been widely used in exor tendon repair due to lack of su cient tensile strength half-life and fear of increased tissue reaction and adhesion formation (Mashadi and Amis 1992a). Of the bioabsorbable sutures with longer tensile strength half-life the properties of polydioxanone (PDS®) and polyglycolide-trimethylene carbonate (Maxon®) sutures have been investigated in vivo in canine exor tendon repair with 4-strand modi ed Kessler repair and active mobilization (Wada et al. 2001a, 2002).

e tendons repaired with coated braided polyester suture healed without initial tensile depression, while polydioxanone repairs decreased signi cantly in strength during the rst two weeks and reached signi cantly lower gap and ultimate force during the six-week follow-up (Wada et al. 2001a). It was assumed that this was due to suture absorption occurring too early, as the in vivo half-life tensile strength of the 4-0 mono lament polydioxanone suture was reported to be four weeks (O´Broin et al. 1993). When the polydioxanone (PDS®) and polyglycolide-trimethylene carbonate (Maxon®) sutures were compared, the latter reached higher tensile strength initially but was signi cantly weaker already a er two weeks due to earlier suture absorption (Wada et al. 2002). In biomechanical testing ex vivo, both polydioxanone and polyglycolide-trimethylene carbonate sutures have demonstrated signi cantly higher elasticity compared to non-absorbable coated braided polyester suture (Bourne et al. 1988).

3.3.7.2. Biocompatibility

e synthetic non-absorbable suture materials commonly used in exor tendon repair, polyester, nylon, and polypropylene, have demonstrated good biocompatibility both experimentally and in human tissue samples taken per operatively or in autopsy (Postlethwaith et al. 1975, Postlethwaith 1979). e tissue reaction to uncoated braided polyester suture was similar to that of the most inert stainless steel and nylon sutures. e braided polyester suture coated with Te on® (Dacron®) showed a slightly increased reaction of histiocytes and lymphocytes. In exor tendon implantation and repair polybutilate coated braided polyester suture (Ethibond®) has demonstrated good biocompatibility (Wada et al. 2001a, Kujala et al. 2004). e tissue reaction caused by polypropylene suture is similar to that of nylon, but in approximately 5% suture fragmentation and/or bone-cartilage-like deposition around the sutures have been reported (Postlethwait 1979).

e bioabsorbable polyglycolide-trimethylene carbonate (Maxon®) suture has been investigated in chicken exor tendon repair with immobilization (Mashadi and Amis 1992a). Increased tissue reaction and adhesion formation was reported compared to the nonabsorbable polybutester (Nova l®) suture. e polyglycolide-trimethylene carbonate (Maxon®), polydioxanone (PDS®), and coated braided polyester (Ethibond®) sutures have been evaluated in canine exor tendon repair with active mobilization (Wada et al. 2001a, 2002). Histologically, the polyester repairs demonstrated maximally only a slight in ammatory reaction, whereas in polydioxanone specimens an in ammatory response surrounding the suture material was seen and increased during the six-week follow-up (Wada et al. 2001a). However, no increase in adhesion formation was detected compared to the polyester repairs. e gross evaluation of the polyglycolide-trimethylene carbonate repairs showed no di erence compared to the polydioxanone repairs (Wada et al. 2002).

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3.4. Tendon repair devices

Several tendon repair devices have been developed with the aim to meet the biomechanical needs of active mobilization. Mersilene mesh sleeve pulled over the tendon ends and attached with the cross-stitch peripheral suture rst introduced by Silfverskiöld and Andersson (1993) and Dacron® splint attached either internally or dorsally (Aoki et al. 1994) reached high ultimate force, but the initial gap forces remained low (Table 1). Also Gordon et al. developed an external stainless steel splint (1999) and an internal stainless steel anchor (1998) which reached high yield force and ultimate force values. However, the suture anchor was a sti , 1-mm thick device which was considered to cause decreased exibility when placed over the interphalangeal joints. A device with two intratendinous stainless steel anchors that are joined by a single multi lament 2-0 stainless steel suture (Teno Fix®) has been investigated experimentally in static (Su et al. 2005a) (Table 1) and cyclic (Wolfe et al. 2007) tensile testing ex vivo, in canine exor tendon repair in vivo (Su et al. 2006), and clinically (Su et al. 2005b). In static tensile testing in situ the Teno Fix® repair reached a higher 2 mm gap force and sti ness compared to the 4-strand cruciate locking repair with 4-0 suture, but also higher energy absorbed to the peak force re ecting increased gliding resistance (Su et al. 2005a). In cyclic loading ex vivo the Teno Fix® device did not demonstrate any biomechanical advantage over the modi ed Kessler and 4-strand cruciate repairs (Wolfe et al. 2007). In canine common super cialis tendon repair with the Teno Fix® and immobilization, no in ammatory reaction interfering with tendon healing was noted. In a clinical study comparing the modi ed Kessler and Teno Fix® repairs with dynamic rehabilitation, good or excellent results were reached in 67% and 70% of the tendons, with rupture rates of 0% and 18%, respectively (Su et al. 2005b).

3.5. Peripheral suture techniques

Originally the circumferential epitendinous suture was considered merely a tiding up suture to improve tendon gliding within the sheath (Lister et al. 1977). Wade et al. (1986) who investigated interrupted simple loops, continuous simple running, and Lembert (vertical mattress) peripheral sutures rst showed that the circumferential suture also contributes signi cantly to the gap resistance and ultimate force of the tendon repair. As many new, stronger epitendinous suture techniques grasp - not only the epitenon - but also the tendon substance, the term peripheral suture has become widely used.

Several new peripheral sutures have been developed and they have shown to improve the gap resistance, sti ness, and ultimate force of the tendon repair (Lin et al. 1988, Wade et al. 1989, Mashadi and Amis 1992b, Silfverskiöld and Andersson 1993, Williams and Amis 1995, Diao et al. 1996, Kubota et al. 1996a, Wang and Tang 2002, Dona et al. 2003, Merrel et al. 2003, Mishra et al. 2003, Wang and Tang 2003) (Table 2). e cross-stitch (Silfverskiöld and Andersson 1993) (Fig. 9A), embedded cross-stitch (Wang and Tang 2003), interlocking cross-stitch and interlocking horizontal mattress (Dona et al. 2003), Lin running locking (Lin et al. 1988) (Fig. 9B), Halsted (horizontal mattress) (Wade et al. 1989) (Fig. 9C), and horizontal intra bre (Mashadi and Amis 1992b) (Fig. 9D) methods with their variations have proved to be the strongest methods, but the complexity of many of these techniques limits their clinical application.

e simple running peripheral suture (Lister et al. 1977) (Fig. 9E) is the most investigated and used technique in exor tendon repair with simple technical performance. Diao et al. (1996) demonstrated that the strength of the running peripheral suture can be increased with

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deeper suture grasps (Fig. 9F). e deep peripheral suture penetrating into the half of the tendon radius reached an 80% greater mean ultimate force and a 90% higher sti ness than the super cial peripheral suture passing through the epitenon only (Table 2). Also the yield force improved signi cantly with the deep running peripheral suture compared to the super cial running peripheral suture (Lotz et al. 1998) (Table 1). Increasing the suture purchase from 1 mm to 2 mm or 3 mm in the running peripheral suture has been shown to improve the ultimate force and to decrease gap formation of the modi ed Kessler and running peripheral suture repair composite (Merrel et al. 2003) (Table 2). Also increasing the number of suture passes in the peripheral suture technique signi cantly increased the gap and ultimate force values of the simple running and other peripheral suture techniques (Kubota et al. 1996a) (Table 2).

3.6. Gliding resistance of tendon repairs

e aim of postoperative mobilization is to improve the functional outcome by keeping the tendon gliding to avoid adhesion formation. e force applied to the tendon during the therapy must exceed the total work of exion needed to ex the digit; otherwise the tendon will not move. e repair strength must be greater than the force applied; otherwise the tendon will rupture (Zhao et al. 2001c).

In the normal state the gliding resistance of the tendon is low, in human exor tendon on the average 0.27 N (Zhao et al. 2001c). e gliding resistance between the pulleys and the repaired FDP tendon has been investigated for various suture techniques ex vivo. All repair methods signi cantly increase the gliding resistance. e number of exposed suture loops and knots outside on the tendon surface, the suture calibre, and the suture material correlate with the tendon gliding resistance (Momose et al. 2000, 2001, Zhao et al. 2001b, 2001c).

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F . Peripheral suture techniques. A. Cross stitch (Silfverskiöld and Andersson 1993), B. Lin (Lin et al. 1988), C. Halsted (Wade et al. 1989), D. Horizontal intra ber (Mashadi and Amis 1992b), E. Simple running (Lister et al. 1977), F. Simple running super cial and simple running deep (Diao et al. 1996).

31

e in uence of suture knots has been investigated in a model without tendon laceration by comparing one volar or one or two lateral knots with di erent suture materials (nylon, braided polyester or coated braided polyester) and suture calibres (5-0 or 4-0) (Momose et al. 2000).

e gliding resistance was the highest with two lateral knots, and higher with one volar than one lateral knot. Also a thicker suture calibre increased the gliding resistance of the knots. Nylon sutures generated less friction than polyester, but the silicone coating of the braided polyester suture (Ticron®) e ectively reduced the gliding resistance.

In a canine model, the smallest increase in the mean gliding resistance due to repair has been reported for the simple running peripheral suture (0.33 N) compared to intact tendon (0.08 N) (Zhao et al. 2001b). However, in a tendon repair the simple running peripheral suture contributes to gliding by increasing gap resistance. Gap formation increases repair gliding resistance signi cantly and may lead to triggering of the repair at the pulley edge (Zhao et al. 2004). Of the commonly used repair composites the modi ed Kessler repair with two strands and one knot between the tendon ends and a simple running peripheral suture has the lowest gliding resistance, on the average 0.27-0.81 N (Momose et al. 2001, Zhao et al. 2001b, 2001c). Other 2-strand techniques which expose more suture material have demonstrated higher mean gliding resistance compared to the modi ed Kessler repair: the Kessler repair with two exposed knots (0.8-1.07 N) and the Tsuge repair with one exposed knot (1.12 N) (Momose et al. 2001, Zhao et al. 2001b, 2001c).

e results over the in uence of the number of strands vary. e modi ed 4-strand Savage repair with one knot between the tendon ends has been reported to have signi cantly higher mean gliding resistance (0.86-1.1 N) compared to the modi ed Kessler repair (0.41-0.81 N) (Zhao et al. 2001b, 2001c). Several multi-strand techniques with knots placed between the tendon ends, such as the 4-strand double modi ed Kessler performed with single-stranded suture (0.31 N) or with looped suture (0.33 N), the 4-strand cruciate repair (0.38 N), and the 6-strand Lim repair (0.32 N), did not increase the gliding resistance signi cantly compared to the modi ed Kessler repair (0.27 N) (Momose et al. 2001). e augmented Becker repair (Fig. 6E) with either four or six strands, and respectively either two or three exposed knots, and multiple exposed loops on the tendon surface, demonstrated the highest gliding resistance of the tested core sutures (0.58-1.52 N) (Momose et al. 2001, Zhao et al. 2001b, 2001c). is was considered to be a consequence of the large amount of suture material exposed on the tendon surface, rather than of the number of strands.

e in uence of locking versus grasping loops on the mean gliding resistance has been investigated comparing the 4-strand modi ed Kessler (grasping) (0.79 N), Pennington (locking) (0.80 N), and modi ed Pennington (locking) (0.87 N) repairs (Tanaka et al. 2004). No signi cant di erences were found.

Also in vivo the postoperative gliding of the tendon depends on the method of repair (Zhao et al. 2002b). In the canine exor tendon with partial 80% laceration the gliding surface of the tendon remodelled with time, and the gliding resistance decreased signi cantly by one and three weeks from repair.

In addition to the suture technique, also tissue oedema due to injury to the subcutaneous tissue and tendon sheath increases the gliding resistance and work of exion in vivo (Lane et al. 1976, Halikis et al. 1997, Cao and Tang 2006). In immediately mobilized tendons the force required to produce full exion increases ten-fold and the total work of exion 90-fold within an hour of injury (Lane et al. 1976), peaking between days four and seven and therea er decreasing

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gradually (Lane et al. 1976, Halikis et al. 1997, Cao and Tang 2006). Immediate mobilization increases the initial gliding resistance and work of exion at ve and seven days from the operation compared to initial immobilization. us, delayed mobilization starting three to ve days from the operation has been suggested (Halikis et al. 1997).

. T

4.1. General healing process

Tendons were long considered to be inert organs which did not contribute to their own healing process but healed only through ingrowth of external granulation tissue, i.e. adhesions (Potenza 1975). e intrinsic capacity of animal tendons to participate in the healing process without extrinsic adhesions was, however, shown in several experimental animal models both in vivo (Matthews and Richards 1974, Lundborg 1976, Lundborg and Rank 1980, Gelberman et al. 1983, 1985) and in vitro (Manske and Lesker 1984, Manske et al. 1985). Also human exor tendons have the ability to mobilize an intrinsic healing response in vitro (Mass and Tuel 1989). In clinical settings both intrinsic and extrinsic pathways occur at the same time. e relative contribution of each depends on factors that relate to injury, surgical repair, and rehabilitation (Matthews and Richards 1976, Gelberman et al. 1983, Strickland 2000, Masuda et al. 2002).

e process of tendon healing in vivo follows a pattern similar to that of other tissues and is divided into three major periods (Gelberman et al. 1983, 1985, Molloy et al. 2003, Strikland 2005).

e in ammatory phase initiates with acute trauma and lasts approximately two to three days from repair. Tissue trauma triggers a coagulation cascade that leads to formation of a clot around the injured area, release of growth factors by platelets and cells in the clot, and invasion of extrinsic cells such as neutrophils and macrophages that clean up necrotic debris and produce more growth factors to initiate a proliferative phase (Gelberman et al. 1985, Gelberman et al. 1991b, Molloy et al. 2003, Strikland 2005, James et al. 2008).

e proliferative phase lasts approximately four weeks. It is characterised by broblast proliferation and migration with production of immature collagen and other extracellular matrix proteins, macrophage invasion, and neovascularisation (Gelberman et al. 1983, 1991b, Khan et al. 1996, Masuda et al. 2002, Molloy et al. 2003, Strikland 2005). In the intrinsic healing major cell proliferation occurs in the epitenon broblasts initiating within three days and peaking around seven days from injury (Gelberman et al. 1983, 1991b, Khan et al. 1996). By then a continuous epitenon cell layer covers the tendon lesion (Gelberman et al. 1991b, Oshiro et al. 2003). In the endotenon an initial decrease in cellularity due to apoptosis occurs with a delayed proliferative response within two to four weeks from trauma (Gelberman et al. 1991b, Khan et al. 1996, Kakar et al. 1998). Increased production of type III procollagen has been detected in the epitenon cells by the third day a er injury, while the expression of type I collagen initially decreases returning to the normal level within four weeks (Oshiro et al. 2003). e relative increase in the type III/I collagen ratio during the early healing period is considered to be part of the normal healing process. In association with pathological dense adhesion formation the relative amount of type III collagen remains lower (Masuda et al. 2002). Revascularization of the area of injury initiates by the third day with ingrowth of proximal vessels in the epitenon progressively extending distally through areas of lower

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vascularity (Gelberman et al. 1983, 1985, 1991a). Early mobilization has been shown to prevent ingrowth of capillary buds via extrinsic adhesion formation.

Finally the remodellation phase lasts till approximately 12 - 20 weeks during which the cellular activity at the repair site decreases and maturation and longitudinal alignment of collagen takes place (Matthews and Richards 1974, Liu et al. 1995, Oshiro et al. 2003). In the normal tendon healing process the relative amounts of type III and I collagen normalize within 12 - 24 weeks from repair (Masuda et al. 2002). A er the remodellation phase only minor di erences compared to the normal tendon structure are found.

4.2. Adhesion formation

Adhesions between the tendon and tendon sheath complicate healing, impairing the gliding mechanism of tendons and leading to decreased function (Lindsay 1960, Matthews and Richards 1976, Gelberman et al. 1983, Seradge 1983, James et al. 2008). Factors a ecting adhesion formation have been largely investigated. e initial injury to the tendon alone does not promote adhesion formation (Matthews and Richards 1974). Unless sutured or immobilized, the edges of the tendon laceration become smoothly rounded and remain free from adhesions within the sheath. Matthews and Richards (1976) investigated the individual and combined e ects of 1) suture insertion, 2) sheath excision, and 3) postoperative immobilization in a rabbit model with incomplete FDP laceration. Suture produced the most adverse e ect with changes suggestive of reduced viability and increased zone of regeneration. In di erent combinations of two factors, the tendency for adhesion formation increased with immobilization and suturing producing the most extensive response. With all three contributing factors, the healing was accompanied by dense, persistent adhesion formation.

Di erent tendon repair techniques have been compared experimentally in vivo to evaluate the extent of trauma to the tendon due to repair and the in uences on tendon healing and adhesion formation. e modi ed Kessler and Tsuge were compared in a canine model with postoperative immobilization, and no di erences were detected in the histological or intravascular dye injection analysis (De no et al. 1986).

Multi-strand techniques have been hypothesized as a ecting adhesion formation by increasing tendon handling, bulk at the repair site, external suture material, and possibly tendon tissue ischaemia (Strickland 2000, Wong et al. 2006). Two- and 4-strand (modi ed Kessler) repairs, both with and without epitendinous suture, have been compared in a chicken exor tendon repair model with four weeks of immobilization (Strick et al. 2004, 2005). Both core suture techniques showed marked adhesion formation, but no di erences in histologic ndings or in the adhesion breaking strength were found. Neither did epitendinous suture have in uence on adhesion formation. Zhao et al. (2001a) compared 2-strand modi ed Kessler and 4-strand modi ed Becker repairs in a canine model of exor tendon repair with passive mobilization and reported that adhesion breaking strength was signi cantly higher in the 4-strand repair at three and six weeks. In the modi ed Becker repair the multiple loops and knots exposed on the tendon surface - rather than the number of strands - have been considered to increase its gliding resistance (Momose et al. 2001, Zhao et al. 2001b, 2001c). us, the high gliding resistance of the modi ed Becker repair was considered to decrease tendon excursion during low-force passive rehabilitation, consequently increasing adhesion formation (Zhao et al. 2001a).

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The association of repair site gap formation with adhesion formation was reported already by Mason and Allen (1941). Lindsay et al. (1960) con rmed that in association with immobilization, gap formation was the major problem leading to poor outcome a er exor tendon repair. e opinions of the size of critical gap formation regarding the healing of mobilized tendons are controversial. Experimentally it has been shown that a gap at the repair site increases tendon gliding resistance and may predispose the tendon to decreased gliding and consequent adhesion formation during postoperative rehabilitation (Zhao et al. 2004). A gap of 2 mm increased the peak gliding resistance with 100% compared to an intact tendon, and with a gap of 3 mm or more all tendons caught at the edge of the A2 pulley causing a dramatically increased peak gliding resistance. In canine exor tendon repair in vivo a gap of 3 mm or more hindered repair strengthening and thus increased the risk of gap formation and rupture during rehabilitation in passively mobilized tendons (Gelberman et al. 1999). However, no in uence on tendon gliding was found. Clinically, a straight correlation between the incidence of gap formation and adhesion formation during controlled motion has been reported, leading to tenolysis in all cases with 4 mm gapping (Seradge 1983). However, gaps of up to 8.5-10 mm have been reported as occasionally well-tolerated with no functional defect in association with controlled motion, suggesting that with adequate mobilization gap-associated adhesion formation may be restricted (Ejeskär and Irstam 1981, Silfverskiöld et al. 1992, Silfverskiöld and May 1993).

Also experimental studies have shown that postoperative controlled early mobilization prevents adhesion formation contributing to the intrinsic healing capacity of the tendons and restoration of the gliding surface (Matthews and Richards 1976, Gelberman et al. 1983, Hitchcock et al. 1987). Several experimental studies have reported healing without adhesion formation a er tendon repair and postoperative active motion (Aoki et al. 1997, Wada et al. 2001a, 2001b).

4.3. In uence of mobilization on tendon healing

4.3.1. Experimental studies in vivo

During immobilization the tensile strength of exor tendon repair diminishes postoperatively reaching the lowest value between ve days and three weeks from the operation (Mason and Allen 1941, Urbaniak et al. 1975, Hitchcock et al. 1987, Wada et al. 2001b). Only 20% (Urbaniak et al. 1975) and 50% (Wada et al. 2001b) of the initial ultimate force has been reported to remain a er one week and 20% a er three weeks (Hitchcock et al. 1987). Urbaniak et al. (1975) and Hitchcock et al. (1987) reported that the initial repair strength was regained a er three weeks and six weeks, respectively. However, Wada et al. (2001b) found that a er six weeks the ultimate force still remained 20% lower than at the time of repair. A er 12 weeks of continuous immobilization the strength of the repaired tendon was only 48% of the strength of the uninjured contralateral control tendon (Gelberman et al. 1982).

Early passive mobilization has been shown to diminish or prevent the initial weakening seen in immobilized tendons (Gelberman et al. 1982, Hatanaka et al. 2000, Boyer et al. 2001a). e strength and sti ness of the repairs subjected to early passive mobilization were signi cantly higher compared to continuously immobilized repairs investigated between three and 12 weeks from the operation (Gelberman et al. 1982). A er 12 weeks the passively mobilized repairs reached 85% of the tensile strength of the intact tendon.

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Early passive mobilization has been shown to improve tendon gliding compared to immobilization measured as linear excursion and angular joint rotation (Gelberman et al. 1982). In canine exor tendon repair increasing the amount of excursion provided by passive rehabilitation with the use of high-excursion (3.5 mm) synergistic wrist motion (synergistic passive wrist extension and nger exion), signi cantly decreased the adhesion grade and the adhesion breaking strength measured a er three and six weeks from repair compared to low excursion (1.5 mm) wrist xation rehabilitation (Zhao et al. 2002a). High excursion synergistic wrist motion therapy has been reported to improve remodelling of the gliding surface and to improve tendon gliding especially with a high friction type of repair (Zhao et al. 2002b). High-force (17 N) & high-excursion (3.5 mm) therapy (simultaneous passive wrist and nger extension) has not been shown to improve tendon excursion, range of motion or tensile properties compared to synergistic wrist motion therapy (Boyer et al. 2001a). Increasing the frequency of controlled passive motion has been shown to accelerate the strengthening of the tendon repair measured a er three and six weeks from repair (Takai et al. 1991).

Active mobilization has been shown to prevent the initial weakening of the tendon repair that occurs in immobilized tendons (Hitchcock et al. 1987, Aoki et al. 1997, Wada et al. 2001a, 2001b) progressively increasing the gap force (Aoki et al. 1997, Wada et al. 2001a, 2001b) and ultimate force (Hitchcock et al. 1987, Wada et al. 2001a) starting from the time of repair. Up to 200% increase in the initial gap force (Wada et al. 2001b) and 50% increase in the ultimate force (Wada et al. 2001a) have been reported at six weeks from repair. Kubota et al. (1996b) who investigated the isolated and combined in uence of motion and tension on the healing of chicken profundus tendons reported that both motion and tension increased the healing response contributing to repair strength, cellular activity, and collagen production with the greatest positive responses achieved when both were applied.

e in uences of postoperative unrestricted (Aoki et al. 1997) and controlled (Wada et al. 2001a, 2001b) active motion on adhesion formation have been investigated in canine exor tendon repair. At three weeks (Aoki et al. 1997) and six weeks (Wada et al. 2001a, 2001b) no adhesion formation was found. Active unrestricted motion has been compared to passive rehabilitation in the healing of repaired and unrepaired partial 60% canine exor tendon laceration (Grewal et al. 1999, 2006). At one and three weeks no signi cant di erences were found in tendon excursion, total joint rotation or macroscopic evaluation of adhesions due to the mobilization used.

4.3.2. Clinical studies

e association of gap formation, tendon excursion during mobilization, and functional outcome a er exor tendon repair has been clinically investigated with intraoperatively inserted metal markers (Seradge 1983, Silfverskiöld et al. 1992, Silfverskiöld and May 1993). In patients treated with controlled motion with rubber band traction, the mean nal repair elongation was on the average 2.6-3.2 mm (range 0-12.5 mm) (Silfverskiöld et al. 1992, Silfverskiöld and May 1993). A seemingly paradoxical weak but not signi cant positive correlation between increasing gap formation and an active interphalangeal joint range of motion was found (Sifverskiöld and May 1993). us, controlled motion with dynamic rubber band traction was e ective in restricting gap-associated adhesion formation. In accordance with the results of Ejeskär and Irstam (1981), gap formation larger than 10 mm resulted in a poor functional outcome. However, Seradge (1983), who also used rubber band traction,

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found a direct correlation between the size of the gap and adhesion formation leading to tenolysis in all cases with 4 mm gapping.

e active range of motion of PIP and DIP joints a er zone II exor tendon repair relates strongly to the amount of tendon excursion produced with early mobilization (Silfverskiöld et al. 1993). e excursion produced with the four- nger rubber band traction with a palmar pulley was approximately twice as long as that achieved with the original one- nger Kleinert splint. With the four- nger splint on the average 2.3 mm of FDP excursion along the middle phalanx and 9.1 mm along the proximal phalanx were measured, corresponding to a mean excursion of 0.4 mm and 1.2 mm per 10 degrees of DIP and PIP joint motion, respectively (Silfverskiöld et al. 1993). Hagberg and Selvik (1991) compared the one- nger Kleinert splint, modi ed four- nger Kleinert splint, and passive exion-active hold exercises in producing tendon excursion in zone II. At the A2 pulley level the normal tendon excursion is considerably longer than at the A3 and A4 levels, and any method of splint rehabilitation may produce su cient excursion. However, at the A3 and A4 levels rubber band traction produced excursion shorter than 1 mm or even negative backward excursion, while active hold exercises produced positive tendon excursion and, despite causing increased repair elongation, yielded signi cantly better results. us, early controlled active motion may be important especially at the A4 pulley level where dynamic splint therapy does not produce su cient excursion (Hagberg and Selvik 1991).

In zone II injuries, the dynamic four- nger rubber band traction splint has been reported to reach excellent or good results in 44% (excellent/good: 36/8 %) to 96% (65/31 %) of patients assessed using the Kleinert criteria (Kleinert et al. 1973) with an average rupture rate of 0-6 % (Gault 1987, Karlander et al. 1993, Adolfsson et al. 1996).

Several investigators have reported improved outcomes of exor tendon repair in zone II a er early active motion rehabilitation (Cullen et al. 1989, Savage and Risitano 1989, Small et al. 1989, Bainbridge et al. 1994, Elliot et al. 1994, Silfverskiöld and May 1994, Baktir et al. 1996, Riaz et al. 1999, Sirotakova and Elliot 2004, Osada et al. 2006). Comparison between the results is di cult due to varying assessment criteria. Bainbridge et al. (1994) and Baktir et al. (1996) compared dynamic rubber-band traction and early active rehabilitation reporting excellent or good results in 54% (28/26 %) and 85% (40/45 %) of patiens a er dynamic rehabilitation, and in 78% (34/44 %) and 94% (67/27 %) of patients a er active rehabilitation assessed with the Strickland criteria (Strickland 1985). On the other hand, Peck et al. (1998) reported excellent or good results in 84% (38/46 %) of tendons with dynamic rehabilitation and in only 59% (17/42 %) of tendons with early active motion, which was due to the higher rupture rate with early active motion (46%) compared to dynamic rehabilitation (7.7%). Also others have reported increased incidence of ruptures due to the higher mobilization forces of active motion commonly ranging between 4 and 10 % when the 2-strand modi ed Kessler core suture with running peripheral suture has been used (Cullen et al. 1989, Small et al. 1989, Bainbridge et al. 1994, Elliot et al. 1994, Baktir et al. 1996). To decrease the rate of ruptures the repair strength has been increased by using either stronger core (Savage and Risitano 1989, Sirotakova and Elliot 2004, Osada et al. 2006) or peripheral sutures (Silfverskiöld and May 1994, Sirotakova and Elliot 1999). e 6-strand Savage with running peripheral suture decreased ruptures to 2.8% (Savage and Risitano 1989). With the cross-stitch peripheral (Fig. 9A) and 2-strand modi ed Kessler sutures a 3.6% rupture rate and 96% (71/25 %) of excellent or good results (Strickland criteria) were reached in the FDP repair (Silfverskiöld and May 1994). In the FPL repair the cross-stitch peripheral suture with the 2-strand modi ed Kessler repair decreased

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the rupture rate from 15% to 8% compared to the results with the running peripheral suture (Sirotakova and Elliot 1999), and when the 4-strand modi ed Kessler repair (Fig. 6A) was combined with cross-stitch peripheral suture, no ruptures occurred (Sirotakova and Elliot 2004). Also with the 6-strand Youshizu (Fig. 7H) and triple-loop (Fig. 7D) core sutures with the running peripheral suture 96% (63/33 %) were graded as excellent or good (Strickland criteria), and no ruptures occurred (Osada et al. 2006).

. P

5.1. Chemical properties

Polylactic acid (PLA) is a hard, pale, linear polymer with thermoplastic properties. Semi-crystalline PLA (molecular weight over 100000 daltons) has a glass transition temperature of 57-58 °C and a melting point of 174-184 °C (Vert et al. 1981, Törmälä et al. 1998). Monomeric lactic acid belongs to the group of alpha-hydroxy acids. A lactic acid molecule is chiral, hence it has two isomers, the L(+)-lactide and D(-)-lactide, with opposite con gurational structures but similar chemical properties. e lactide is a cyclic diester of lactic acid and exists as four di erent compounds, the LL (L-lactide, i.e. levolactide) and DD (D-lactide, i.e. dextrolactide) antipodes, the DL isomer (mesolactide), and the DD+LL solid combination (racemic lactide) (Vert et al. 1981) (Fig. 10).

e high-molecular-weight polymers suitable for surgical devices are produced with ring opening polymerization of lactide cyclic diesters (Fig. 11). Poly-L-lactic acid, i.e. PLLA, consists of only the L-isomer. Copolymerization of the monomers results in a random copolymer (Vert et al. 1981, Andriano et al. 1994, Törmälä et al. 1998). e polylactic acid stereocopolymers, which contain both isomers, are named by the relative amount of L-lactide compared to D-lactide, e.g. PLDLA 96/4 (= poly-96L/4D-lactic acid). e relative amounts of L- and D-con gurations a ect the physical and chemical properties of the stereocopolymers. PLDLA stereocopolymers with a molar ratio of less than 87.5/12.5 are intrinsically amorphous. With

HH

CH3CH3

O

OO

OO

OO

OH H

CH3CH3

O

OO

OH

H

CH3CH3

O

OO

OO

OO

O HH

HH

CH3CH3

CH3CH3

rac-lactide

D-lactideL-lactide

DL-lactidei.e. mesolactide

L-lactic D-lactic

PLA-stereocopolymer

PLA-homopolymer

H

C

CH3

COO[ ]

H

C

CH3

O CO[ O C CO ]

CH3

H

F . e four stereoisomers of lactide. F . e structure of polylactides.

R L

38

an increased amount of D-lactide, a greater disorder of L-lactide sequence occurs in the copolymer decreasing crystallinity, melting temperature, viscoelasticity, and strength of a polymer.

5.2. Biodegradation

e degradation and loss of strength of bioabsorbable polymers may be a ected by several factors causing variation in the properties of compounds with the same name (Törmälä et al. 1998). ese factors can be divided into 1) microstructural [chemical composition (hydrophilic; hydrophobic), molecular weight and molecular weight distribution, impurities (monomers, oligomers, catalysers, colours, etc.), crystallinity, molecular orientation, matrix/reinforcement morphology, porosity, surface quality], 2) macrostructural [size and geometry of an implant, weight/surface area ratio], and 3) environmental [tissue environment, storage conditions] factors.

PLA and the copolymers of L- and D-lactides are biodegraded mainly by hydrolysis (non-speci c hydrolytic scission) to lactic acid, which becomes incorporated in the citric acid cycle and is excreted predominantly by the lungs as carbon dioxide and water (Kulkarni et al. 1966, Brady et al. 1973, Cordewener et al. 1995). Loss of molecular weight due to hydrolysis, which splits the chemical bonds of long polymers, is the rst sign of degradation. Loss of mechanical strength properties precedes changes in the macroscopic form of an implant, which is followed by mass loss and nally ingestion of polymer debris by phagocytic cells (Cordewener et al. 1995, Pietrzak et al. 1997, Törmälä and Rokkanen 2001). e complete degradation and resorption of PLLA material in vivo proceeds slowly and takes several years (Majola 1992, Pietrzak et al. 1997).

Less crystalline stereocopolymers of L-lactide with D- or DL-lactide are less hydrophobic and have thus faster degradation rates than 100% pure PLLA, the rate depending on the monomer ratios (Vert et al. 1981, Bergsma et al. 1995, Cordewener et al. 1995, Törmälä et al. 1998). On the basis of mass-loss studies, the incorporation of 4% D-lactide enhances degradation by a factor of two (Bergsma et al. 1995). e degradation of surgical mono lament PLDLA 96/4 suture has been investigated previously (Kangas et al. 2001). e in vitro half-life tensile strength of 0.2 mm thick (3-0 calibre) suture was reported as 10-13 weeks, and a er six weeks of subcutaneous implantation in the rabbit the suture retained approximately 75% of its initial tensile strength. e degradation rate and strength retention of PLDLA 96/4 in vitro and in vivo do not di er signi cantly (Saikku-Bäckström et al. 1999, Kangas et al. 2001).

5.3. Biocompatibility

e biocompatibility of PLLA materials has been investigated in many experimental and clinical studies. Experimental short-term and long-term follow-ups up to ve years as well as clicnical studies have reported good biocompatibility of PLLA implants (Majola 1992, Törmälä et al. 1998, Törmälä and Rokkanen 2001). In ammatory reaction related to the bioabsorption has been reported in approximately 0.1% of cases presenting a er several years due to the long hydrolysing period and crystallinity of the material.

Good biocompatibility of the PLDLA 96/4 copolymer has been reported, characterized as a mild foreign-body reaction (Cordewener et al. 1995, Saikku-Bäckström et al. 2001, Kangas et al. 2006, Waris et al. 2008). Bergsma et al. (1995) and De Jong et al. (2005) reported very mild histological reaction to non-degraded PLA96 discs comparable to polyethylene

R L

39

implanted subcutaneously in rats. In vitro predegraded PLA96 demonstrated a slightly enhanced histological reaction during in vivo implantation with increased amounts of macrophages and polymer debris accompanied with granulomatous in ammatory reaction. Good biocompatibility of PLDLA 96/4 nails and rods in bone xation in the rabbit has been reported even during end-stage degradation at three years (Saikku-Bäckström et al. 2001). Also PLDLA 96/4 joint sca old arthroplasty for small joint reconstruction in minipigs showed good biocompatibility and almost total degradation during a three-year follow-up (Waris et al. 2008). In the rabbit Achilles tendon implanted PLDLA 96/4 suture demonstrated good biocompatibility with formation of a signi cantly thinner brous tissue capsule and fewer in ammatory cells compared to polyglyconate suture (Maxon®) during a 12 –week follow-up (Kangas et al. 2006).

R L

40 T T

. E

x vi

vo st

atic

tens

ile te

stin

g st

udie

s on

tend

on re

pair

tech

niqu

es.

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tech

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ture

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Perip

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d

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e (N

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Ulti

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gr

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ng

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ump

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ture

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(N)

(N

/mm

) fo

rce

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Ang

eles

et a

l. 20

02

Mod

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ker

lock

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t 4-

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rlock

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M

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*

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64 *

Ro

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St

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lock

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este

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ny

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*

Aok

i et a

l. 19

94

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ler

gras

ping

2

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ple

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0 pp

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tial)

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nitia

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29

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24 (i

nitia

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81

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este

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ple

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0 pp

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tial)

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ors.

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t -

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ter

simpl

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n.

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nitia

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78

Aok

i et a

l. 19

95c

Sa

vage

lo

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2 1

out

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ple

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7-

0 pp

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al)

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Sa

vage

lo

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este

r sim

ple

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7-

0 pp

- 9

(initi

al)

- 12

Sa

vage

lo

ckin

g 4

4 2

out

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poly

este

r sim

ple

run.

7-

0 pp

- 13

(ini

tial)

- 33

Sa

vage

lo

ckin

g 4

4 4

out

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poly

este

r sim

ple

run.

7-

0 pp

- 10

(ini

tial)

- 28

Sa

vage

lo

ckin

g 4

4 4

in

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poly

este

r sim

ple

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7-

0 pp

- 12

(ini

tial)

- 23

Sa

vage

lo

ckin

g 6

6 3

out

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poly

este

r sim

ple

run.

7-

0 pp

- 19

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tial)

- 47

Sa

vage

lo

ckin

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6 6

out

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poly

este

r sim

ple

run.

7-

0 pp

- 12

(ini

tial)

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Sa

vage

lo

ckin

g 6

6 6

in

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poly

este

r sim

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Barr

ie e

t al.

2000

b

Mod

. Kes

sler

? 2

2 1

in

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este

r ru

n. lo

ck

6-0

ny

-

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m)

- 39

*

Dou

ble

Kess

ler

? 4

4 2

in

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este

r ru

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ck

6-0

ny

-

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lock

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* (2

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2 1

in

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r ru

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-

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*

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lock

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Mod

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ple

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ng (=

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3 40

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m

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ing

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lon

simpl

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n.

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ny

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(ini

tial)

4.8

39

purc

hase

1.0

cm

lo

ckin

g 4

2 1

in

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ple

run.

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0 ny

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nitia

l) 5.

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od. S

avag

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lock

ing

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0 ny

lon

simpl

e ru

n.

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ny

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(ini

tial)

5.0

41

Din

opou

los e

t al.

2000

M

od. K

essle

r gr

aspi

ng

4 2

1 in

4-

0 ny

lon

simpl

e ru

n.

6-0

pp

- 40

(1m

m)/

32(3

mm

)

58

Mod

. dou

ble

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ler

gras

ping

8

4 1

in

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nylo

n sim

ple

run.

6-

0 pp

-

70 (1

mm

)/28

(3m

m)

87

Don

a et

al.

2004

C

ruci

ate

lock

ing

w

idth

10%

4

2 1

in

4-0

poly

prop

.

-

- -

13 (2

mm

) 2.

5 36

25%

4

2 1

in

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poly

prop

.

-

- -

13 (2

mm

) 4.

1 46

33%

4

2 1

in

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poly

prop

.

-

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9 (2

mm

) 3.

7 45

50%

4

2 1

in

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poly

prop

.

-

-

- 9

(2m

m)

3.6

40

25

%

4 2

1 in

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0 po

lypr

op.

simpl

e ru

n.

4-0

pp

- 33

(2m

m)

7.7

47

25

%

4 2

1 in

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0 po

lypr

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X-s

titch

4-

0 pp

-

37 (2

mm

) 9.

2 67

25%

4

2 1

in

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poly

prop

. IH

M

4-0

pp

- 46

(2m

m)

9.9

80

Gor

don

et a

l. 19

98

Kess

ler

? 2

2 ?

4-0

nylo

n

-

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22

Beck

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prop

.

-

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-

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In

tern

. ste

el a

ncho

r -

- -

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0 st

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-

-

74

-

- 75

e re

sults

are

from

line

ar te

nsile

test

ing

exce

pt w

hen

othe

rwise

mar

ked:

* in

situ

tens

ile te

st r

esul

t; **

cu

rvili

near

tens

ile te

st r

esul

t. e

plac

emen

t of t

he k

nots

mar

ked

as: i

n =

betw

een

the

tend

on e

nds

or: o

ut =

on

the

tend

on s

urfa

ce. O

ther

sym

bols:

?

= no

t de

ned

or u

ncle

arly

de

ned

in t

he s

tudy

, - =

not

mea

sure

d or

doe

s no

t exi

st,

mod

. = m

odi

ed, s

impl

e run

. = si

mpl

e run

ning

, run

. loc

k. =

runn

ing

lock

ed, X

-stit

ch =

cros

s-st

itch,

inte

rlock

= in

terlo

ckin

g, IH

M =

inte

rlock

ing

horiz

onta

l mat

tres

s, ny

= n

ylon

, pp

= p

olyp

ropy

lene

, stu

mp

= th

e cu

t ten

don

end.

42 T

Gor

don

et a

l. 19

99

Kess

ler

gras

ping

2

2 ?

4-0

nylo

n

-

- 20

- -

23

Beck

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poly

prop

.

-

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22

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ge

lock

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37

-

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Ex

tern

. ste

el sp

lint

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4-0

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l

-

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- -

60

+ Ke

ssle

r gr

aspi

ng

2 2

? 4-

0 ny

lon

Hat

anak

a an

d M

ansk

e 19

99

Mod

. Pen

ning

ton

lock

ing

are

a/lo

op 5

%

2 2

- 3-

0 po

lyes

ter

-

-

-

- -

54

1

5%

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0 po

lyes

ter

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-

-

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62

2

5%

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66

over

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-

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Hat

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00

Mod

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ton

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ter

simpl

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(ini

tial)

- 46

lock

ing

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1 in

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0 po

lyes

ter

simpl

e ru

n.

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pp

- 47

(ini

tial)

- 68

lock

ing

2 2

1 in

2-

0 po

lyes

ter

simpl

e ru

n.

6-0

pp

- 66

(ini

tial)

- 90

M

od. K

essle

r gr

aspi

ng

2 2

1 in

4-

0 po

lyes

ter

simpl

e ru

n.

6-0

pp

- 42

(ini

tial)

- 50

gras

ping

2

2 1

in

3-0

poly

este

r sim

ple

run.

6-

0 pp

-

49 (i

nitia

l) -

60

gr

aspi

ng

2 2

1 in

2-

0 po

lyes

ter

simpl

e ru

n.

6-0

pp

- 52

(ini

tial)

- 74

Hot

okez

aka

and

Man

ske

1997

2-

stra

nd o

ne te

ndon

no

loop

s 2

1 -

3-0

poly

este

r

-

- -

-

- 21

end

mod

el

gras

ping

2

3 -

3-0

poly

este

r

-

- -

-

- 34

lock

ing

2 3

- 3-

0 po

lyes

ter

-

-

-

- -

51

2

seria

l gra

spin

g 2

5 -

3-0

poly

este

r

-

- -

-

- 46

2 se

rial l

ocki

ng

2 5

- 3-

0 po

lyes

ter

-

-

-

- -

47

Kom

andu

ri e

t al.

1996

D

orsa

l

Bu

nnel

l gr

aspi

ng

2 ?

? 4-

0 ny

lon

simpl

e ru

n.

6-0

ny

-

- -

22 *

Ke

ssle

r ?

2 2

? 4-

0 ny

lon

simpl

e ru

n.

6-0

ny

-

- -

24 *

Ke

ssle

r ?

2 2

? 4-

0 ny

lon

simpl

e ru

n.

6-0

ny

-

- -

30 *

T

. Ex

vivo

stat

ic te

nsile

test

ing

stud

ies o

n te

ndon

repa

ir te

chni

ques

.

C

ore

tech

niqu

e Lo

ckin

g/

Stra

nds

Grip

s/

Kno

ts

Cor

e su

ture

Pe

riphe

ral

Perip

h.

Yiel

d

Gap

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e (N

) St

ine

ss

Ulti

mat

e

gr

aspi

ng

st

ump

tech

niqu

e su

ture

fo

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(N)

(N

/mm

) fo

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(N)

43T

Pa

lmar

Bu

nnel

l gr

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? 4-

0 ny

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-

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12 *

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0 ny

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n.

6-0

ny

-

- -

15 *

Ke

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r ?

2 2

? 4-

0 ny

lon

simpl

e ru

n.

6-0

ny

-

- -

18 *

Kub

ota

et a

l. 19

98

Mod

. Kes

sler

lock

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1 ou

t 5-

0 po

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(initi

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3.1

13

Mod

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ler

lock

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0 po

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ter

-

-

- 5

(initi

al)

7.7

29

Mod

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ble

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ler

lock

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1 ou

t 5-

0 po

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ter

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titch

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0 pp

-

21 (i

nitia

l) 17

.7

60

Mod

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ble

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ler

lock

ing

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1 ou

t 5-

0 po

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-

-

- 5

(initi

al)

7.9

39

Mod

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ble

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ler

lock

ing

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1 ou

t 5-

0 po

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X-s

titch

6-

0 pp

-

26 (i

nitia

l) 17

.4

61

Kus

ano

et a

l. 19

99

Mod

. Kes

sler

lock

ing

2 2

1 in

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0 ny

lon

4 st

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s 6-

0 ny

-

11 (1

mm

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14

Dou

ble

loop

ed

lock

ing

4 2

2 ou

t 5-

0 lo

op n

ylon

4

stitc

hes

6-0

ny

- 13

(1m

m)

- 28

Tr

iple

loop

ed (=

Tang

) lo

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g 6

3 3

out

5-0

loop

nyl

on

4 st

itche

s 6-

0 ny

-

18 (1

mm

) -

39

Yous

hizu

lo

ckin

g 6

3 1

in,1

out

5-0

loop

nyl

on

4 st

itche

s 6-

0 ny

-

19 (1

mm

) -

30

Laba

na e

t al.

2001

Ke

ssle

r-Ta

jima

? 2

2 2

in ?

4-0

nylo

n sim

ple

run.

6-

0 pp

-

30 (i

nitia

l) -

32

Dou

ble

loop

ed

lock

ing

4 2

2 ou

t 4-

0 lo

op n

ylon

sim

ple

run.

6-

0 pp

-

41 (i

nitia

l) -

48

Trip

le lo

oped

(=Ta

ng)

lock

ing

6 3

3 ou

t 4-

0 lo

op n

ylon

sim

ple

run.

6-

0 pp

-

56 (i

nitia

l) -

64

Law

renc

e an

d D

avis

200

5

Cru

ciat

e cr

oss-

stitc

h lo

ckin

g 4

2 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

36 (i

nitia

l) 6.

0 47

C

ruci

ate

cros

s-st

itch

lock

ing

4 2

1 in

4-

0 po

lypr

op.

simpl

e ru

n.

6-0

ny

- 52

(ini

tial)

8.0

63

Cru

ciat

e cr

oss-

stitc

h lo

ckin

g 4

2 1

in

4-0

poly

este

r sim

ple

run.

6-

0 ny

-

52 (i

nitia

l) 10

.2

66

Cru

ciat

e cr

oss-

stitc

h lo

ckin

g 4

2 1

in

4-0

stee

l sim

ple

run.

6-

0 ny

-

66 (i

nitia

l) 11

.9

87

Cru

ciat

e cr

oss-

stitc

h lo

ckin

g 4

2 1

in

4-0

poly

ethy

lene

sim

ple

run.

6-

0 ny

-

63 (i

nitia

l) 12

.8

81

Lee

1990

Kess

ler

? 2

2 ?

4-0

poly

este

r

-

- -

-

- 23

D

OLL

S lo

ckin

g 4

4 2

in

4-0

loop

pol

yest

. -

- -

-

- 37

e res

ults

are f

rom

line

ar te

nsile

testi

ng ex

cept

whe

n ot

herw

ise m

arke

d: *

in si

tu te

nsile

test

resu

lt.

e pla

cem

ent o

f the

kno

ts m

arke

d as

: in

= be

twee

n th

e ten

don

ends

or:

out =

on

the

tend

on su

rface

. Oth

er sy

mbo

ls: ?

= n

ot d

ene

d or

unc

learly

de

ned

in th

e stu

dy, -

= n

ot m

easu

red

or d

oes n

ot ex

ist, m

od. =

mod

ied

, sim

ple r

un. =

sim

ple r

unni

ng, X

-stit

ch =

cros

s-sti

tch,

D

OLL

S =

Dou

ble l

oop

lock

ing

sutu

re, n

y =

nylo

n, p

p =

poly

prop

ylen

e, stu

mp

= th

e cut

tend

on en

d.

44 T

Lotz

et a

l. 19

98

Inta

ct te

ndon

! -

- -

- -

- -

- -

35.9

-

Mod

. Kes

sler

lock

ing

2 2

1 in

4-

0 ny

lon

- -

10

- 2.

9 12

sim

ple

run.

- -

- -

- -

-sup

erci

al

6-0

pp

11

- 5.

0 15

-

- -

- -

- -d

eep

6-0

pp

23

- 12

.1

31

Mod

. Kes

sler

lock

ing

2 2

1 in

4-

0 ny

lon

-sup

erci

al

6-0

pp

16

- 8.

2 22

M

od. K

essle

r lo

ckin

g 2

2 1

in

4-0

nylo

n -d

eep

6-0

pp

30

- 12

.7

39

McL

arne

y et

al.

1999

M

od. K

essle

r ?

2 2

1 in

4-

0 po

lyes

ter

simpl

e ru

n.

6-0

pp

- 22

(2m

m)

- 28

St

rickl

and

lo

ck. &

gra

sp.

4 3

4 in

4-

0 po

lyes

ter

simpl

e ru

n.

6-0

pp

- 23

(2m

m)

- 35

M

od. S

avag

e lo

ckin

g 4

4 4

out

4-0

poly

este

r sim

ple

run.

6-

0 pp

-

21 (2

mm

) -

32

Cru

ciat

e gr

aspi

ng

4 2

1 ou

t 4-

0 po

lyes

ter

simpl

e ru

n.

6-0

pp

- 44

(2m

m)

- 56

Mill

er e

t al.

2007

St

rickl

and

gras

p. &

lock

. 4

3 2

in

3-0

nylo

n sim

ple

run.

5-

0 ny

-

39 (2

mm

) -

50

Stric

klan

d gr

asp.

& lo

ck.

4 3

2 in

3-

0 po

lyes

ter

simpl

e ru

n.

5-0

ny

- 43

(2m

m)

- 49

St

rickl

and

gras

p. &

lock

. 4

3 2

in

3-0

poly

ethy

lene

sim

ple

run.

5-

0 ny

-

43 (2

mm

) -

53

Mod

. Bec

ker

lock

ing

4 6

2 in

3-

0 ny

lon

simpl

e ru

n.

5-0

ny

- 48

(2m

m)

- 69

M

od. B

ecke

r lo

ckin

g 4

6 2

in

3-0

poly

este

r sim

ple

run.

5-

0 ny

-

58 (2

mm

) -

82

Mod

. Bec

ker

lock

ing

4 6

2 in

3-

0 po

lyet

hyle

ne

simpl

e ru

n.

5-0

ny

- 60

(2m

m)

- 12

4

Nog

uchi

et a

l. 19

93

Kess

ler

gras

ping

2

2 2

out

4-0

nylo

n sim

ple

run.

6-

0 ny

-

- -

24 *

Ta

jima

gras

ping

2

2 2

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

- -

31 *

Ts

uge

lock

ing

2 1

1 ou

t 4-

0 lo

op p

olye

st.

simpl

e ru

n.

6-0

ny

- -

- 27

*

Sava

ge

lock

ing

4 4

1 in

4-

0 ny

lon

simpl

e ru

n.

6-0

ny

- -

- 53

*

Lee

gras

ping

4

2 2

in

4-0

loop

pol

yest

. sim

ple

run.

6-

0 ny

-

- -

38 *

Prui

tt e

t al.

1996

Sa

vage

lo

ckin

g 4

4 4

in

5-0

poly

este

r -

- -

- -

23

Sava

ge

lock

ing

4 4

4 ou

t 5-

0 po

lyes

ter

- -

- -

- 34

T

. E

x vi

vo st

atic

tens

ile te

stin

g st

udie

s on

tend

on re

pair

tech

niqu

es.

C

ore

tech

niqu

e Lo

ckin

g/

Stra

nds

Grip

s/

Kno

ts

Cor

e su

ture

Pe

riphe

ral

Perip

h.

Yiel

d

Gap

forc

e

Sti

ness

U

ltim

ate

gras

ping

stum

p

te

chni

que

sutu

re

forc

e (N

) (N

) (N

/mm

) fo

rce

(N)

45T R

ober

tson

and

Al-Q

atta

n 19

92

Mod

. Kes

sler

? 2

2 ?

3-0

poly

prop

. -

- -

22 (i

nitia

l) -

35

Robe

rtso

n gr

aspi

ng

4 2

1 in

3-

0 po

lypr

op.

- -

- 46

(ini

tial)

-

52

Stric

klan

d lo

ck. &

gra

sp.

4 3

? 3-

0 po

lypr

op.

- -

- 17

(ini

tial)

- 30

Sava

ge 1

985

Sa

vage

lo

ckin

g 6

6 1

in

4-0

poly

este

r -

- -

- -

67

Sava

ge

lock

ing

6 6

3 in

4-

0 po

lyes

ter

- -

- -

- 59

Shai

eb a

nd S

inge

r 199

7

Mod

. Kes

sler

lock

ing

? 2

2 1

in

4-0

poly

este

r -

- -

16 (2

mm

) -

18

Mod

. dou

ble

Kess

ler

lock

ing

? 4

4 2

in

4-0

poly

este

r -

- -

32 (2

mm

) -

39

Mod

. trip

le K

essle

r lo

ckin

g ?

6 6

3 in

4-

0 po

lyes

ter

- -

- 50

(2m

m)

- 55

Sa

vage

lo

ckin

g ?

6 6

1 in

4-

0 po

lyes

ter

- -

- 63

(2m

m)

- 70

Silfv

ersk

iöld

and

And

erss

on 1

993

M

od. K

essle

r lo

ckin

g ?

2 2

1 in

4-

0 po

lyes

ter

- -

- 20

N:g

ap4.

7mm

-

27

Mod

. Kes

sler

lock

ing

? 2

2 1

in

4-0

poly

este

r sim

ple

run.

vol

. 6-

0 pd

-

20N

:gap

0.8m

m

- 38

M

od. K

essle

r lo

ckin

g ?

2 2

1 in

4-

0 po

lyes

ter

simpl

e ru

n.

6-0

pd

- 20

N:g

ap0.

2mm

-

48

- -

- -

- -

X-s

titch

6-

0 pd

-

20N

:gap

0mm

-

63

Mes

h sle

eve

- -

- -

- X

-stit

ch

6-0

pd

- 20

N:g

ap0.

2mm

-

103

Slad

e et

al.

2001

M

od. K

essle

r ?

2 2

1 in

4-

0 po

lyes

ter

simpl

e ru

n.

6-0

ny

- 14

(2m

m)

- 39

*

Mod

.dou

ble

Kess

ler

? 4

4 ?

4-0

poly

este

r sim

ple

run.

6-

0 ny

-

26 (2

mm

) -

66 *

Sa

vage

lo

ckin

g 6

6 ?

4-0

poly

este

r sim

ple

run.

6-

0 ny

-

56 (2

mm

) -

124

*

Mod

. Kes

sler +

?

2 2

1 in

4-

0 po

lyes

ter

simpl

e ru

n.

6-0

ny

- 88

(2m

m)

- 14

0 *

d

orsa

l gra

Smith

and

Eva

ns 2

001

M

od. K

essle

r ?

2 2

1 in

4-

0 po

lyes

ter

simpl

e ru

n.

6-0

pp

- -

- 31

M

od d

oubl

e Ke

ssle

r ?

4 4

1 in

,1 o

ut 4

-0 p

olye

ster

sim

ple

run.

6-

0 pp

-

- -

52

Soej

ima

et a

l. 19

95

Dor

sal m

od. K

essle

r gr

aspi

ng ?

2 2

1 in

4-

0 ny

lon

simpl

e ru

n.

6-0

pp

- -

8.0

36

Palm

ar m

od. K

essle

r gr

aspi

ng ?

2 2

1 in

4-

0 ny

lon

simpl

e ru

n.

6-0

pp

- -

7.2

28

e re

sults

are

from

line

ar te

nsile

test

ing

exce

pt w

hen

othe

rwise

mar

ked:

* in

situ

tens

ile te

st re

sult.

e

plac

emen

t of t

he k

nots

mar

ked

as: i

n =

betw

een

the

tend

on e

nds o

r: ou

t = o

n th

e te

ndon

surf

ace.

Oth

er sy

mbo

ls: ?

= n

ot d

ene

d or

unc

lear

ly d

ene

d in

the s

tudy

, - =

not

mea

sure

d or

doe

s not

exist

, mod

. = m

odi

ed, s

impl

e run

. = si

mpl

e run

ning

, vol

. = v

olar

, X-s

titch

=

cros

s-st

itch,

ny

= ny

lon,

pp

= po

lypr

opyl

ene,

pd =

pol

ydio

xano

ne, s

tum

p =

the c

ut te

ndon

end.

46 T

Stei

n et

al.

1998

D

orsa

l

K

essle

r gr

aspi

ng

2 2

2 ou

t 4-

0 ny

lon

simpl

e ru

n.

6-0

ny

- 24

(2m

m)

- 29

Str

ickl

and

lock

ing

2 2

2 in

4-

0 ny

lon

simpl

e ru

n.

6-0

ny

- 27

(2m

m)

- 34

Rob

erts

on

gras

ping

4

2 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

34 (2

mm

) -

41

M

od. B

ecke

r lo

ckin

g 4

8 2

out

4-0

nylo

n sim

ple

run.

6-

0 ny

-

49 (2

mm

) -

59

Palm

ar

Kes

sler

gras

ping

2

2 2

out

4-0

nylo

n sim

ple

run.

6-

0 ny

-

21 (2

mm

) -

28

S

tric

klan

d lo

ckin

g 2

2 2

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

24 (2

mm

) -

32

R

ober

tson

gr

aspi

ng

4 2

1 in

4-

0 ny

lon

simpl

e ru

n.

6-0

ny

- 35

(2m

m)

- 40

Mod

. Bec

ker

lock

ing

4 8

2 ou

t 4-

0 ny

lon

simpl

e ru

n.

6-0

ny

- 53

(2m

m)

- 59

Su e

t al.

2005

a

Cru

ciat

e

lock

ing

4 2

? 4-

0 po

lyes

ter

- -

- 29

* (2

mm

) 8.

5 *

45 *

C

ruci

ate

lo

ckin

g 4

2 ?

3-0

poly

este

r -

- -

32 *

(2m

m)

9.2

* 50

*

Teno

Fix

an

chor

coi

l 1

1 -

2-0

stee

l -

- -

39 *

(2m

m)

10.5

* 45

*

Cru

ciat

e

lock

ing

4 2

? 4-

0 po

lyes

ter

run.

lock

. 6-

0 pp

-

47 *

(2m

m)

14.8

* 70

*

Cru

ciat

e

lock

ing

4 2

? 3-

0 po

lyes

ter

run.

lock

. 6-

0 pp

-

54 *

(2m

m)

17.8

* 74

*

Teno

Fix

an

chor

coi

l 1

1 -

2-0

stee

l ru

n. lo

ck.

6-0

pp

- 55

* (2

mm

) 16

.0 *

67 *

Tan

and

Tang

200

4

Mod

. Kes

sler

perp

endi

c.lo

ckin

g

p

urch

ase

3mm

2

2 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

20 (2

mm

) -

25

4

mm

2

2 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

23 (2

mm

) -

29

7

mm

2

2 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

24 (2

mm

) -

29

10

mm

2

2 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

29 (2

mm

) -

36

12

mm

2

2 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

27 (2

mm

) -

32

Cru

ciat

e pe

rpen

dic.

lock

ing

p

urch

ase

3mm

4

2 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

25 (2

mm

) -

39

7

mm

4

2 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

34 (2

mm

) -

40

10

mm

4

2 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

37 (2

mm

) -

49

Mod

. Kes

sler

horis

ont.

lock

ing

pur

chas

e 7m

m

2 2

1 in

4-

0 ny

lon

simpl

e ru

n.

6-0

ny

- 18

(2m

m)

- 24

C

ruci

ate

obliq

ue lo

ckin

g

p

urch

ase

7mm

4

4 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

33 (2

mm

) -

42

T

. E

x vi

vo st

atic

tens

ile te

stin

g st

udie

s on

tend

on re

pair

tech

niqu

es.

C

ore

tech

niqu

e Lo

ckin

g/

Stra

nds

Grip

s/

Kno

ts

Cor

e su

ture

Pe

riphe

ral

Perip

h.

Yiel

d

Gap

forc

e (N

) St

ine

ss

Ulti

mat

e

gr

aspi

ng

st

ump

tech

niqu

e su

ture

fo

rce

(N)

(N

/mm

) fo

rce

(N)

47T

Tana

ka e

t al.

2004

M

od.K

essle

r gr

aspi

ng

4 2

1 in

4-

0 lo

op n

ylon

sim

ple

run.

6-

0 ny

-

27 (1

mm

) -

34

Penn

ingt

on

lock

ing

4 2

1 in

4-

0 lo

op n

ylon

sim

ple

run.

6-

0 ny

-

27 (1

mm

) -

39

Mod

.Pen

ning

ton

lock

ing

4 2

1 in

4-

0 lo

op n

ylon

sim

ple

run.

6-

0 ny

-

29 (1

mm

) -

48

Mod

ied

Lee

gr

aspi

ng

4 4

2 in

4-

0 lo

op n

ylon

sim

ple

run.

6-

0 ny

-

18 (1

mm

) -

38

Lock

ing

Lee

lock

ing

4 4

2 in

4-

0 lo

op n

ylon

sim

ple

run.

6-

0 ny

-

20 (1

mm

) -

41

Tang

et a

l. 20

01b

M

od. K

essle

r lo

ckin

g ?

2 2

1 in

3-

0 ny

lon

simpl

e ru

n.

5-0

ny

- 23

(2m

m)

6.2

28

Mod

. Kes

sler

lock

ing

? 2

2 1

in

3-0

nylo

n X

-stit

ch

5-0

ny

- 47

(2m

m)

7.7

68

Mod

. Kes

sler

lock

ing

? 2

2 1

in

3-0

nylo

n H

alst

ed

5-0

ny

- 62

(2m

m)

7.2

82

Tang

(Trip

le lo

oped

) lo

ckin

g 6

3 3

out

4-0

loop

nyl

on s

impl

e ru

n.

5-0

ny

- 44

(2m

m)

7.5

56

Tang

(Trip

le lo

oped

) lo

ckin

g 6

3 3

out

4-0

loop

nyl

on X

-stit

ch

5-0

ny

- 72

(2m

m)

9.2

95

Tang

(Trip

le lo

oped

) lo

ckin

g 6

3 3

out

4-0

loop

nyl

on H

alst

ed

5-0

ny

- 87

(2m

m)

10.0

11

7

Tang

et a

l. 20

03a

M

od. K

essle

r gr

aspi

ng

con

vent

iona

l 2

2 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

14 (2

mm

) -

20

obl

ique

2

2 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

18 (2

mm

) -

22

len

gthe

ned

2 2

1 in

4-

0 ny

lon

simpl

e ru

n.

6-0

ny

- 21

(2m

m)

- 25

M

od. K

essle

r lo

ckin

g

c

onve

ntio

nal

2 2

1 in

4-

0 ny

lon

simpl

e ru

n.

6-0

ny

- 16

(2m

m)

- 21

o

bliq

ue

2 2

1 in

4-

0 ny

lon

simpl

e ru

n.

6-0

ny

- 20

(2m

m)

- 26

l

engt

hene

d 2

2 1

in

4-0

nylo

n sim

ple

run.

6-

0 ny

-

25 (2

mm

) -

29

Tang

et a

l. 20

05

Mod

. Kes

sler

gras

ping

pu

rcha

se 4

mm

2

2 ?

4-0

nylo

n sim

ple

run.

6-

0 ny

-

12 (i

nitia

l) -

19

7

mm

2

2 ?

4-0

nylo

n sim

ple

run.

6-

0 ny

-

14 (i

nitia

l) -

24

10

mm

2

2 ?

4-0

nylo

n sim

ple

run.

6-

0 ny

-

13 (i

nitia

l) -

26

12

mm

2

2 ?

4-0

nylo

n sim

ple

run.

6-

0 ny

-

13 (i

nitia

l) -

25

4-st

rand

tech

niqu

e lo

ckin

g

purc

hase

4m

m

4 2

2 in

4-

0 ny

lon

simpl

e ru

n.

6-0

ny

- 20

(ini

tial)

- 38

10m

m

4 2

2 in

4-

0 ny

lon

simpl

e ru

n.

6-0

ny

- 25

(ini

tial)

- 43

e res

ults

are f

rom

line

ar te

nsile

testi

ng ex

cept

whe

n ot

herw

ise m

arke

d: *

in si

tu te

nsile

test

resu

lt.

e pla

cem

ent o

f the

kno

ts m

arke

d as

: in

= be

twee

n th

e ten

don

ends

or:

out =

on

the

tend

on su

rface

. Oth

er sy

mbo

ls: ?

= no

t de

ned

or u

ncle

arly

de

ned

in th

e stu

dy, -

= n

ot m

easu

red

or d

oes n

ot ex

ist, m

od. =

mod

ied

, sim

ple r

un. =

sim

ple r

unni

ng, X

-stit

ch =

cros

s-sti

tch,

in

terlo

ck =

inte

rlock

ing,

ny

= ny

lon,

stum

p =

the c

ut te

ndon

end.

48 T

Tara

s et a

l. 20

01

Mod

. Kes

sler

gras

ping

2

2 2

in

5-0

poly

este

r -

- -

- -

16

Dou

ble

gras

ping

lo

ckin

g 2

2 2

in

5-0

poly

este

r -

- -

- -

14

Mod

. Bun

nell

lock

ing

2 2

2 in

5-

0 po

lyes

ter

- -

- -

- 12

M

od. K

essle

r gr

aspi

ng

2 2

2 in

4-

0 po

lyes

ter

- -

- -

- 22

D

oubl

e gr

aspi

ng

lock

ing

2 2

2 in

4-

0 po

lyes

ter

- -

- -

- 23

M

od. B

unne

ll lo

ckin

g 2

2 2

in

4-0

poly

este

r -

- -

- -

24

Mod

. Kes

sler

gras

ping

2

2 2

in

3-0

poly

este

r -

- -

- -

31

Dou

ble

gras

ping

lo

ckin

g 2

2 2

in

3-0

poly

este

r -

- -

- -

37

Mod

. Bun

ell

lock

ing

2 2

2 in

3-

0 po

lyes

ter

- -

- -

- 36

M

od. K

essle

r gr

aspi

ng

2 2

2 in

2-

0 po

lyes

ter

- -

- -

- 41

D

oubl

e gr

aspi

ng

lock

ing

2 2

2 in

2-

0 po

lyes

ter

- -

- -

- 57

M

od. B

unne

ll lo

ckin

g 2

2 2

in

2-0

poly

este

r -

- -

- -

59

Wad

a et

al.

2000

M

od.d

oubl

e Ke

ssle

r lo

ckin

g 4

4 1

in

3-0

poly

este

r -

- -

25 (2

mm

) 6.

8 46

M

od.d

oubl

e Ke

ssle

r gr

aspi

ng

4 4

1 in

3-

0 po

lyes

ter

- -

- 20

(2 m

m)

6.4

38

Cru

ciat

e lo

ckin

g 4

2 1

in

3-0

poly

este

r -

- -

22 (2

mm

) 6.

7 40

C

ruci

ate

gras

ping

4

2 1

in

3-0

poly

este

r -

- -

20 (2

mm

) 5.

9 36

Wan

g et

al.

2003

Ta

ng (T

riple

loop

ed)

lock

ing

6 3

3 ou

t 4-

0 lo

op n

ylon

sim

ple

run.

6-

0 ny

-

45 /

38 **

(2m

m)

- 59

/ 51

**

Mod

. Tan

g lo

ckin

g 6

3 3

out

4-0

loop

nyl

on

simpl

e ru

n.

6-0

ny

- 46

/ 36

** (2

mm

) -

62 /

57 **

Xie

et a

l. 20

02

Mod

. Sav

age

lock

ing

6 3

1 in

4-

0 ny

lon

simpl

e ru

n.

6-0

ny

- 37

** (2

mm

) -

58 /

48 **

Ta

ng (T

riple

loop

ed)

lock

ing

6 3

3 ou

t 4-

0 lo

op n

ylon

sim

ple

run.

6-

0 ny

-

45 **

(2m

m)

- 60

/ 49

**

Lim

lo

ckin

g 6

2 2

in

4-0

loop

nyl

on

simpl

e ru

n.

6-0

ny

- 40

** (2

mm

) -

51 /

42 **

T

. E

x vi

vo st

atic

tens

ile te

stin

g st

udie

s on

tend

on re

pair

tech

niqu

es.

C

ore

tech

niqu

e Lo

ckin

g/

Stra

nds

Grip

s/

Kno

ts

Cor

e su

ture

Pe

riphe

ral

Perip

h.

Yiel

d

Gap

forc

e (N

) St

ine

ss

Ulti

mat

e

gr

aspi

ng

st

ump

tech

niqu

e su

ture

fo

rce

(N)

(N

/mm

) fo

rce

(N)

49T

Tara

s et a

l. 20

01

Mod

. Kes

sler

gras

ping

2

2 2

in

5-0

poly

este

r -

- -

- -

16

Dou

ble

gras

ping

lo

ckin

g 2

2 2

in

5-0

poly

este

r -

- -

- -

14

Mod

. Bun

nell

lock

ing

2 2

2 in

5-

0 po

lyes

ter

- -

- -

- 12

M

od. K

essle

r gr

aspi

ng

2 2

2 in

4-

0 po

lyes

ter

- -

- -

- 22

D

oubl

e gr

aspi

ng

lock

ing

2 2

2 in

4-

0 po

lyes

ter

- -

- -

- 23

M

od. B

unne

ll lo

ckin

g 2

2 2

in

4-0

poly

este

r -

- -

- -

24

Mod

. Kes

sler

gras

ping

2

2 2

in

3-0

poly

este

r -

- -

- -

31

Dou

ble

gras

ping

lo

ckin

g 2

2 2

in

3-0

poly

este

r -

- -

- -

37

Mod

. Bun

ell

lock

ing

2 2

2 in

3-

0 po

lyes

ter

- -

- -

- 36

M

od. K

essle

r gr

aspi

ng

2 2

2 in

2-

0 po

lyes

ter

- -

- -

- 41

D

oubl

e gr

aspi

ng

lock

ing

2 2

2 in

2-

0 po

lyes

ter

- -

- -

- 57

M

od. B

unne

ll lo

ckin

g 2

2 2

in

2-0

poly

este

r -

- -

- -

59

Wad

a et

al.

2000

M

od.d

oubl

e Ke

ssle

r lo

ckin

g 4

4 1

in

3-0

poly

este

r -

- -

25 (2

mm

) 6.

8 46

M

od.d

oubl

e Ke

ssle

r gr

aspi

ng

4 4

1 in

3-

0 po

lyes

ter

- -

- 20

(2 m

m)

6.4

38

Cru

ciat

e lo

ckin

g 4

2 1

in

3-0

poly

este

r -

- -

22 (2

mm

) 6.

7 40

C

ruci

ate

gras

ping

4

2 1

in

3-0

poly

este

r -

- -

20 (2

mm

) 5.

9 36

Wan

g et

al.

2003

Ta

ng (T

riple

loop

ed)

lock

ing

6 3

3 ou

t 4-

0 lo

op n

ylon

sim

ple

run.

6-

0 ny

-

45 /

38 **

(2m

m)

- 59

/ 51

**

Mod

. Tan

g lo

ckin

g 6

3 3

out

4-0

loop

nyl

on

simpl

e ru

n.

6-0

ny

- 46

/ 36

** (2

mm

) -

62 /

57 **

Xie

et a

l. 20

02

Mod

. Sav

age

lock

ing

6 3

1 in

4-

0 ny

lon

simpl

e ru

n.

6-0

ny

- 37

** (2

mm

) -

58 /

48 **

Ta

ng (T

riple

loop

ed)

lock

ing

6 3

3 ou

t 4-

0 lo

op n

ylon

sim

ple

run.

6-

0 ny

-

45 **

(2m

m)

- 60

/ 49

**

Lim

lo

ckin

g 6

2 2

in

4-0

loop

nyl

on

simpl

e ru

n.

6-0

ny

- 40

** (2

mm

) -

51 /

42 **

Xie

et a

l. 20

05

2-st

rand

tech

niqu

e ci

rcle

lock

ing

di

am. 1

mm

2

1 1

in

4-0

nylo

n sim

ple

run.

6-

0 pp

-

17 (2

mm

) -

21

2 m

m

2 1

1 in

4-

0 ny

lon

simpl

e ru

n.

6-0

pp

- 24

(2 m

m)

- 29

3

mm

2

1 1

in

4-0

nylo

n sim

ple

run.

6-

0 pp

-

23 (2

mm

) -

26

4-st

rand

tech

niqu

e ci

rcle

lock

ing

di

am. 1

mm

4

2 2

in

4-0

nylo

n sim

ple

run.

6-

0 pp

-

24 (2

mm

) -

36

2 m

m

4 2

2 in

4-

0 ny

lon

simpl

e ru

n.

6-0

pp

- 35

(2 m

m)

- 44

3

mm

4

2 2

in

4-0

nylo

n sim

ple

run.

6-

0 pp

-

33 (2

mm

) -

42

Xie

and

Tan

g 20

05

4-st

rand

lock

ing

tech

n.

expo

sed

cros

s 4

2 2

in

4-0

nylo

n sim

ple

run.

6-

0 pp

-

24 (i

nitia

l) -

42

4-st

rand

lock

ing

tech

n.

embe

dded

cro

ss

4 2

2 in

4-

0 ny

lon

simpl

e ru

n.

6-0

pp

- 26

(ini

tial)

- 42

4-

stra

nd lo

ckin

g te

chn.

ci

rcle

lock

4

2 2

in

4-0

nylo

n sim

ple

run.

6-

0 pp

-

25 (i

nitia

l) -

44

Zatit

i et a

l. 19

98

Mod

. Kes

sler

? 2

2 1

in

4-0

poly

este

r sim

ple

run.

6-

0 pp

-

32 (i

nitia

l) -

34

Mod

. Kes

sler

? 2

2 1

in

4-0

poly

este

r H

alst

ed

6-0

pp

- 44

(ini

tial)

- 48

Sa

vage

lo

ckin

g 6

3 1

in

4-0

poly

este

r -

- -

36 (i

nitia

l) -

67

Robe

rtso

n gr

aspi

ng

4 2

1 in

4-

0 po

lyes

ter

- -

- 13

(ini

tial)

- 36

-

- -

- -

- X

-stit

ch

6-0

pp

- 27

(ini

tial)

- 35

-

- -

- -

- sim

ple

run.

6-

0 pp

-

16 (i

nitia

l) -

20

e re

sults

are

from

line

ar te

nsile

test

ing

exce

pt w

hen

othe

rwise

mar

ked:

** c

urvi

linea

r ten

sile

test

resu

lt.

e pl

acem

ent o

f the

kno

ts m

arke

d as

: in

= be

twee

n th

e te

ndon

end

s or

: out

= o

n th

e te

ndon

sur

face

. Oth

er s

ymbo

ls: ?

= n

ot d

ene

d or

unc

lear

ly d

ene

d in

the

stud

y, -

= n

ot m

easu

red

or d

oes

not e

xist

, dia

m. =

dia

met

re, m

od. =

mod

ied

, sim

ple

run.

= si

mpl

e ru

nnin

g, X

-stit

ch =

cro

ss-s

titch

, ny

= ny

lon,

pp

= po

lypr

opyl

ene,

stum

p =

the

cut t

endo

n en

d.

50 T T

. E

x vi

vo st

atic

tens

ile te

stin

g st

udie

s on

perip

hera

l sut

ure

tech

niqu

es.

C

ore

repa

ir Pe

riphe

ral

Perip

hera

l G

ap fo

rce

St

ine

ss

Ulti

mat

e

te

chni

que

sutu

re

(N)

(N/m

m)

forc

e (N

)

Dia

o et

al.

1996

Mod

. loc

king

Kes

sler

Sim

ple

runn

ing

2- s

tran

d, 4

-0 n

ylon

su

per

cial

6-

0 po

lypr

op.

- 6.

8 22

deep

6-

0 po

lypr

op.

- 12

.9

39

Don

a et

al.

2003

no

cor

e su

ture

Si

mpl

e ru

nnin

g 6-

0 po

lypr

op.

23 (2

mm

) 7.

6 31

Cro

ss-s

titch

6-

0 po

lypr

op.

21 (2

mm

) 8.

1 42

IXS

6-0

poly

prop

. 20

(2m

m)

8.7

49

IH

M

6-0

poly

prop

. 26

(2m

m)

10.1

53

Kub

ota

et a

l. 19

96

no c

ore

sutu

re

Sim

ple

runn

ing

pa

sses

1

0 6-

0 po

lypr

op.

7 (in

itial

) -

12

14

6-0

poly

prop

. 9

(initi

al)

- 14

1

8 6-

0 po

lypr

op.

14 (i

nitia

l) -

22

Sim

ple

lock

ing

p

asse

s

1

0 6-

0 po

lypr

op.

3 (in

itial

) -

11

14

6-0

poly

prop

. 5

(initi

al)

- 11

1

8 6-

0 po

lypr

op.

9 (in

itial

) -

18

Lem

bert

mat

tres

s

pass

es

10

6-0

poly

prop

. 6

(initi

al)

- 21

1

4 6-

0 po

lypr

op.

8 (in

itial

) -

22

18

6-0

poly

prop

. 10

(ini

tial)

- 28

Hal

sted

mat

tres

s

pass

es

10

6-0

poly

prop

. 4

(initi

al)

- 21

1

4 6-

0 po

lypr

op.

7 (in

itial

) -

24

18

6-0

poly

prop

. 12

(ini

tial)

- 28

Cro

ss-s

titch

pass

es

10

6-0

poly

prop

. 6

(initi

al)

- 28

1

4 6-

0 po

lypr

op.

6 (in

itial

) -

30

18

6-0

poly

prop

. 10

(ini

tial)

- 38

51T

Lin-

lock

ing

pa

sses

1

0 6-

0 po

lypr

op.

5 (in

itial

) -

30

14

6-0

poly

prop

. 9

(initi

al)

- 41

1

8 6-

0 po

lypr

op.

13 (i

nitia

l) -

63

Lin

et a

l. 19

88

no c

ore

sutu

re

Sim

ple

runn

ing

6-0

poly

diax

an.

- 3.

7 6

Lem

bert

runn

ing

6-0

poly

diax

an.

- 4.

8 15

Lin

6-0

poly

diax

an.

- 6.

0 24

Mer

rel e

t al.

2003

no

cor

e su

ture

Si

mpl

e ru

nnin

g

1 m

m

6-0

nylo

n -

- 15

2 m

m

6-0

nylo

n -

- 31

3 m

m

6-0

nylo

n -

- 38

M

od. l

ocki

ng K

essle

r Si

mpl

e ru

nnin

g

2-

stra

nd, 3

-0 p

olye

ster

1

mm

6-

0 ny

lon

20N

:gap

2.2m

m

- 37

2 m

m

6-0

nylo

n 20

N:g

ap1.

4mm

-

51

3

mm

6-

0 ny

lon

20N

:gap

1.0m

m

- 53

Wad

e et

al.

1989

M

od.g

rasp

ing

Kess

ler

- -

3 (in

itial

) -

22

2-st

rand

, 5-0

stee

l Si

mpl

e ru

nnin

g 5-

0 po

lyes

ter

22 (i

nitia

l) -

42

H

alst

ed m

attr

ess

5-0

poly

prop

. 39

(ini

tial)

- 70

Hal

sted

mat

tres

s 5-

0 po

lydi

axan

. 42

(ini

tial)

- 77

Hal

sted

mat

tres

s 5-

0 po

lyes

ter

42 (i

nitia

l) -

79

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52

AIMS OF THE STUDY

e present experiments were designed to develop a new su ciently strong and yet simple exor tendon repair technique performed with bioabsorbable suture to meet the biomechanical

requirements of early active mobilization.

In detail the aims of the study were the following:

1. To study the initiation and pattern of disruption of the repair composite with di erent core suture techniques. To investigate the biomechanical in uence of the di erent structural properties of the core suture (the number of strands, suture con guration, and suture calibre) on the strength of the repair composite (I).

2. To examine the biomechanical material and knot properties of the bioabsorbable PLDLA 96/4 suture to evaluate its suitability for exor tendon repair compared to the widely used coated braided polyester suture (Ticron®) (II).

3. To investigate biomechanically two new variations of the Pennington modi ed Kessler repair, performed with the triple-stranded suture or triple-stranded bound suture of coated braided polyester (Ticron®), developed on the basis of the results of Study I (III).

4. To investigate the biomechanical properties of the Pennington modi ed Kessler repair performed with the new bioabsorbable PLDLA 96/4 triple-stranded bound suture, developed on the basis of the Studies II and III, comparing it to the Savage repair (Ticron®), a traditional 6–strand technique (IV).

A S

53

MATERIALS AND METHODS

. T

Studies I, III, and IV

e biomechanical testing of di erent tendon repair techniques in the Studies I, III, and IV was performed in fresh pig hind leg extensor digiti quarti proprius tendons. Fresh pig trotters were collected from the abattoir and stored at –20°C. For the experiments each was thawed to room temperature, and the extensor digiti quarti proprius tendon was dissected out just before use.

e specimens were kept moist by spraying with 0.9% saline during preparation and testing. Altogether 100 tendons were used during the study, ten specimens in each group.

. S

Studies I-IV

e coated braided polyester suture (Ticron®, Davies & Geck, San Isidro, Dominican Republic), of either 4-0 or 3-0 calibre was used as core suture material in the tendon repairs (Studies I, III, IV) and of 3-0 calibre in biomechanical material and knot testing (Study II).

e 6-0 mono lament polypropylene suture (Prolene®, Ethicon, Hamburg, Germany) was used as peripheral suture material in all tendon repairs (Studies I, III, IV).

For the polylactide sutures (Studies II, IV), the raw material used was a copolymer of L/D lactid acid (PLDLA) with an L/D monomer ratio of 96/4 and intrinsic viscosity of 4.98 dL/g (PURAC Biochem B.V., Netherlands). e multi lament polylactide bres were melt-spun using Gimac micro-extruder (Gimac, Castronno, Italy) with a die temperature of 272°C (Study II) or 270°C (Study IV) and oriented at elevated temperatures in a three-step process to the

nal draw ratio of 4,25 (Study II) or 4,26 (Study IV). e nal mean diameter of the laments was 0.09 mm. Six laments were twisted, folded in the middle, and twisted again to form a 12- lament twine. e sutures were washed in ethanol, dried in vacuum for 16 hours, packed individually, and sterilized by gamma irradiation with a minimum dose of 2.5 Mrad. e mean diameter of the PLDLA suture was 0.45 mm.

. R

Study I

Five di erent core suture techniques which were variations of the Pennington modi ed Kessler and 6-strand Savage repairs were investigated (Fig. 12) (Table 3). e suture techniques varied in regard to 1) the number of core suture strands, 2) the suture con guration, and 3) the suture calibre, to evaluate the in uence of each on the biomechanical properties.

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54

e modi ed Kessler, 3-0 suture (2K3): e repair was performed in Pennington´s locking con guration (Pennington 1979) with 10 mm suture purchase in each tendon end. e knot was placed between the transsected tendon ends.

e double modi ed Kessler, 3-0 suture (4K3): First a modi ed Kessler suture was inserted as described for the 2K3 repair. en another modi ed Kessler suture was placed with 7 mm suture purchase, thus producing a double modi ed Kessler. e repair was performed in an interrupted pattern; thus two knots were placed between the tendon ends.

e 4-strand Savage, 3-0 suture (4S3): e repair consists of two double cross-stitches in each tendon end and four strands crossing the repair site. e suture purchase was 10 mm in each tendon end, and the width of each cross-stitch was 2 mm. e repair was performed in an interrupted pattern; thus two knots were placed between the tendon ends.

e 4-strand Savage, 4-0 suture (4S4): e repair was performed as described for the 4S3 repair.

e 6-strand Savage, 4-0 suture (6S4): e repair consists of three double cross-stitches in each tendon end and six suture strands crossing the repair site. e sutures were performed in an interrupted pattern (Savage 1985); thus three knots were placed between the tendon ends.

M M

T . e experimental design of the tendon repair tensile testing studies.

Study Group Core technique Core suture material Tensile testing

I 2K3 Pennington 3-0 coated braided Static modi ed Kessler polyester

4K3 Double Pennington 3-0 coated braided Static modi ed Kessler polyester

4S3 4-strand Savage 3-0 coated braided Static polyester

4S4 4-strand Savage 4-0 coated braided Static polyester

6S4 6-strand Savage 4-0 coated braided Static polyester

III 3S Pennington triple-stranded Static modi ed Kessler suture (polyester)

3SB Pennington triple-stranded bound Static modi ed Kessler suture (polyester)

IV PLDLA Pennington PLDLA triple-stranded Static & cyclic modi ed Kessler bound suture

Savage 6-strand Savage 4-0 coated braided Cyclic polyester

All repairs included a simple running peripheral suture of 6-0 mono lament polypropylene. Ten specimens were included in each group.

55

Each repair was completed with a simple running peripheral suture with 12 loops which penetrated one quarter of the tendon radius.

Study III

Triple-stranded sutures and triple-stranded bound sutures were made in laboratory conditions. Under 2.5 x magni cation three 3-0 coated braided polyester sutures (Ticron®, Davies & Geck, San Isidro, Dominican Republic) were inserted into a 21 gauge injection needle cut to the length of 15 mm to form the triple-stranded suture.

For the triple-stranded bound suture the three 3-0 polyester suture strands were then bound together parallel to each other side by side with 7-0 mono lament polypropylene suture (Prolene®, BV-1 taper point needle, Ethicon, G.m.b.H, Hamburg, Germany) passing obliquely to and fro through at an angle of 45 degrees with the long axis of the braided polyester sutures (5 passes per cm) (Fig. 13).

F . e tendon repair techniques in Study I. Pennington modi ed Kessler, 3-0 suture (2K3); Double Pennington modi ed Kessler, 3-0 suture (4K3); 4-strand Savage, 3-0 suture (4S3); 4-strand Savage, 4-0 suture (4S4); 6-strand Savage, 4-0 suture (6S4).

F . Schematic picture of the coated braided polyester triple-stranded bound suture.

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56

Two di erent 6-strand repair techniques were investigated (Fig. 14) (Table 3): e triple-stranded suture (3S) and triple-stranded bound suture (3SB) of coated braided polyester in the Pennington modi ed Kessler con guration (Pennington 1979). For knotting, the three strands were separated in both ends of the bound suture and tied in pairs. us three knots were placed between the tendon ends. e repairs were completed with a simple running peripheral suture with 12 loops.

Study IV

For the polylactide triple-stranded bound sutures, the polylactide sutures were rst made as described in Chapter 2. ree sutures were then tied parallel to each other side by side with two double laments threaded over and beneath in turn (Fig. 15). e nal width and thickness of the PLDLA triple-stranded bound sutures were 1.630 mm and 0.580 mm, respectively. e end of the PLDLA triple-stranded bound suture was xed into the cut end of a 15 mm long 21 gauge injection needle. e sutures were washed in ethanol, dried in vacuum for 16 hours, packed individually, and sterilized by gamma irradiation with a minimum dose of 2.5 Mrad.

e PLDLA repair: e 6-strand Pennington modi ed Kessler repairs (Pennington 1979) for static and cyclic testing were performed with PLDLA triple-stranded bound suture (Table 3). For knotting the three strands were separated in both ends of the triple-stranded bound suture and tied in pairs. us three knots were placed between the tendon ends.

e Savage repair: e 6-strand Savage repairs (Savage 1985) for the cyclic testing were performed with 4-0 coated braided polyester suture as described for Study I (Table 3).

Each repair was completed with a simple running peripheral suture of 6-0 polypropylene with 12 loops.

M M

F . Schematic picture of the PLDLA triple-stranded bound suture.

F . In Study III the Pennington modi ed Kessler repairs were performed with the triple-stranded suture (3S) and triple-stranded bound suture (3SB) of coated braided polyester.

57

. K

Study II

A total of 170 surgical knot con guration specimens were investigated: 90 coated braided polyester suture (Table 6) and 80 PLDLA 96/4 suture (Table 7) knots. e knot con gurations, chosen on the basis of previous studies (Holmlund 1974, Tera and Åberg 1976, Trail et al. 1989) and the pilot study by the present author, are presented according to the system described by Tera and Åberg (1976), in which the number of wraps in each throw is indicated by an Arabic number, the relationship being either parallel (square knot indicated by =) or crossed (granny knot indicated by x) between each throw. e knot was performed by tying the suture material around a plastic tube with an outer diameter of 6 cm. e suture loop was then divided on the opposite side of the knot for biomechanical tensile testing.

On the basis of biomechanical knot testing, the best two knot con gurations for both materials were chosen for morphometric analyses to compare the size of the smallest secure knots between the materials.

Studies I, III, and IV

In all core sutures performed with coated braided polyester suture (Studies I, III, IV) each knot consisted of one double throw and three single square throws (2=1=1=1) to form a secure knot (Holmlund 1974). With PLDLA suture (Study IV), three square throws (1=1=1) were used to form a secure knot.

. B

5.1. Static tensile testing

Studies I-IV

Static tensile testing of the suture materials, knot con gurations, and tendon repair techniques was performed with a tensile testing machine (LR Series Material Testing Machine LR30K, Lloyd Instruments Limited, Hampshire, UK). For the testing each specimen was adjusted between the clamps of the tensile testing machine. e initial distance between the clamps was always 35 mm corresponding to the calculated length of each suture strand including one loop at both ends in the Pennington modi ed Kessler core suture. A preload of 0.1 N was used in the material and knot testing. With the tendon repairs no preload was used (Chapter 5.1.3). e specimen was distracted at a constant speed depending on the testing sample (Chapters 5.1.1 Material testing, 5.1.2 Knot testing, and 5.1.3 Tendon repair testing). e load-deformation data were collected with a computerised data acquisition system (R Control for Windows, Lloyd Instruments Ltd., Hampshire, UK), and a load-deformation curve was produced for each specimen (Fig. 16).

e middle third of the linear slope of the load-deformation curve was de ned to analyse the sti ness (N/mm) of the specimen by setting an o set line along the linear slope of the curve.

e rst linear point and yield point were de ned as the points of divergence of the o set line

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58

from the load-deformation curve. e strain (mm/mm) and force (N) at the rst linear point (SFL and FFL), yield point (SY and FY), and ultimate point (SU and FU) were de ned. Strain at each point was de ned as repair site deformation (the change in distance between the tendon clamps at each point) divided by the initial distance between the clamps.

5.1.1. Material testing

Study II

e material testing according to the United States Pharmacopeia (USP) (Table 5) includes testing of an unknotted suture strand and a suture strand with a standardized simple knot, which is tied by placing one end of the strand over the other and through the loop thus formed and by pulling the knot tight. e suture was distracted at a constant speed of 70 mm/min de ned according to the USP standards to equal twice the gauge length per minute (USP 2002).

Material testing according to the USP includes the de ning of three variables: the tensile strength and the elongation at tensile strength of the unknotted suture, and the knot tensile strength of the standardized simple knot suture. e tensile strength and the knot tensile strength are equivalent to the ultimate force (FU) of the specimens. e elongation at tensile strength is de ned as the percentage extension of the unknotted suture to the initial gauge length and is equivalent to the strain at the ultimate point (SU).

In addition to the USP variables, also the strain and force at the rst linear point (SFL and FFL) and the strain and force at the yield point (SY and FY) as well as the sti ness (Stif) were de ned for all specimens (Chapter 5.1.)

e material testing was also performed at a distraction rate of 20 mm/min. is was carried out to allow comparison of the testing results to those of the knot testing (Chapter 5.1.2.), to the static tensile testing results of the tendon repair techniques (Studies I, III, IV), and to previous static tensile testing studies on tendon repairs, commonly using the distraction rate of

M M

Load

(N)

Extension (mm)

A

B

C

F . Load deformation curve (as an exemple a 4-strand Savage repair with 3-0 suture). Initial non-linear toe region ends at the rst linear point (A) followed by the linear region which ends at the yield point (B). An o set line along the linear slope of the curve was used to de ne the rst linear point and yield point as the points of divergence of the o set line from the load-deformation curve. e yield point is followed by the failure region. e ultimate point (C) is the maximum point of the curve.

59

20 mm/min (Noguchi et al. 1993, Silfverskiöld and Andersson 1993, Shaieb and Singer 1997, Lotz et al. 1998, Winters et al. 1998, Smith and Evans 2001, Taras et al. 2001).

5.1.2. Knot testing

Study II

e tested knot specimens were distracted at a static rate of 20 mm/min until the suture broke at the knot level or the knot failed totally by slippage.

e load-deformation curve was analysed (Chapter 5.1.). In addition, the knot holding capacity (KHC) and strain at KHC (SKHC) were de ned. KHC is the force at which the knotted strand fails either by breakage or the knot starts to slide. KHC and the corresponding SKHC were de ned by a visual analysis of the specimen during testing and by analysing the load-deformation curve. A knot was considered to be secure when knot slippage did not occur, and the biomechanical properties did not improve signi cantly by increasing the number of throws.

5.1.3. Tendon repair testing

Studies I, III, and IV

Immediately a er repair each tendon specimen was placed in the tensile testing machine (Chapter 5.1.). e repair was placed halfway between the tendon clamps. A piece of graphpaper with 1 mm graduated markings was placed vertically behind the clamps, parallel with the tendon, and a digital watch placed beside the tendon specimen was started simultaneously with the tensile testing. e test was recorded with the video camera (Sony Handycam CCD-TR425E) at a rate of 25 frames/second. Each specimen was distracted at a static rate of 20 mm/min, and the load-deformation curve was produced (Fig. 16). To eliminate the possibility of varying tightness of the specimens in the tensile testing machine, load values below 1 N and the corresponding extension values from the load-deformation data were excluded before analysing the results.

e sti ness (Stif), as well as strain and force at the rst linear point (SFL and FFL), yield point (SY and FY), and ultimate point (SU and FU) were analysed from the load-deformation curve as described in Chapter 5.1. e appearance and development of gap formation at the repair site was analysed by frame-by-frame playback on the video recorder. Both partial and total 1, 2, and 3 mm gaps were de ned. For example, the gap was considered to be partial 1 mm when the maximum opening of the repair site was 1 mm. e gap was considered to be total 1 mm when the minimum opening of the repair site was 1 mm. e time point of each gap event was used to determine the corresponding extension and load values from the load-deformation data.

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5.2. Cyclic tensile testing

Study IV

Cyclic tensile testing was performed with the servo hydraulic testing machine (Instron Fast Track 8801, Instron, High Wycombe, UK). e testing set-up was identical to that of static tensile testing of the tendon repairs (Chapter 5.1.3.). During the test force was applied and released by a computer controlled pneumatic piston. A custom-written WaveMaker program (Instron, High Wycombe, UK) controlled the pressure valves to obtain the desired loading rate and number of cycles. A 100 N dynamic load cell (Dynacell 100 N, type 2527-132, Instron, High Wycombe, UK) was used. No preload was applied; the initial load was manually adjusted to zero. All tendons were rst subjected to 4000 cycles till 35 N. e applied force was increased in 10-N increments for an additional 4000 cycles at each new load level until the appearance of a total 3 mm gap. e cycle rate was 1.5 mm/s at 35 N, 2.0 mm/s at 45 N, 2.25 mm/s at 55 N, and 2.25 mm/s at 65 N. e minimum and maximum extension data for every one hundredth cycles, and the appearance of partial and total 1, 2, and 3 mm gaps with the corresponding number of cycles were recorded. Gap formation was measured when the force was in its minimum. e product of the number of cycles and the applied load (Newton-cycles) for partial 1, 2, and 3 mm and total 1, 2, and 3 mm gap formation were calculated.

. M Study II

To compare the size of the two optimal PLDLA suture and coated braided polyester suture (Ticron®) knots chosen on the basis of the biomechanical properties from static tensile testing, a morphometrical analysis of the knots was performed. e cross-sectional area of each knot was measured under a microscope (Leitz Diaplan; Ernst Leitz, Wetzlar, Germany) linked via a videocamera (Color View II, So , So Imaging System G.m.b.H., Münster, Germany) to a computer (Dell, Ireland). AnalySIS docu 3.2 (So -Imaging So ware GmbH, Münster, Germany) was used for the image analysis. e magni cation used was 25 x at the screen. e error of the morphometrical method was measured by the coe cient of variation as 1.2%.

Study III

e mean width of the triple-stranded suture and triple-stranded bound suture was de ned morphometrically (Analysis 3.2; Olympus So Imaging Solutions, Berlin, Germany) with ten randomly selected points along the whole length of one specimen using a microscope (Leitz Diaplan; Ernst Leitz, Wetzlar, Germany) with 60 x magni cation at the screen.

. S Studies I-IV

All results are presented as mean values and 95% con dence intervals. All statistical analyses were performed with SPSS 11.0 for Windows (SPSS Inc., Chicago, IL, USA). A p value of less than 0.05 was considered signi cant.

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In Study I, all data were analysed using the analysis of variance (ANOVA), and, when found signi cant, independent-samples T-test was used for comparison between the groups in regard to one variable at a time – 1) the number of strands (2K3 and 4K3, 4S4 and 6S4), 2) the suture calibre (4S3 and 4S4), 3) suture con guration (4K3 and 4S3) – to evaluate the e ect of each on the de ned biomechanical parameters. e paired-samples t-test was used to analyse the di erences within the groups [yield force (FY) vs. ultimate force (FU)].

In Study II, the results from material testing were analysed to investigate the in uence of knotting and distraction speed on the PLDLA and coated braided polyester sutures. e analysis was performed using one-way ANOVA and when found signi cant, depending on the equality of variances, either the Bonferroni or Tamhane post-hoc multiple comparisons test was used. e analysis of the biomechanical results of di erent knot con gurations was performed in regard to ve square throws (1=1=1=1=1) for coated braided polyester and two square throws (1=1) for PLDLA using the one-way between groups ANOVA with planned comparisons. e statistical comparison of the biomechanical properties and knot size of the best two PLDLA and coated braided polyester suture knots was performed using the one-way ANOVA and Bonferroni multiple comparisons test.

In Study III, all data were analysed with the independent-samples T-test.

In Study IV, a statistical comparison of the Newton-cycles at partial 1, 2, and 3 mm and total 1, 2, and 3 mm gap formation between the examination groups was performed using the independent-samples T-test.

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62 R

RESULTS

. D

(I)

1.1. Mode of failure of the repairs

In all repairs failure was initiated by disruption of the peripheral suture in the proximity of the yield point (Fig. 18). e core sutures failed a er the peripheral suture. Mode of failure of the core suture was determined by the suture calibre. All ten 4-strand Savage and nine out of ten of the 6-strand Savage repairs performed with 4-0 suture failed by suture rupture before reaching total gap formation. All the modi ed Kessler repairs performed with 3-0 suture failed by suture pullout with a mean gap size of 13.2 mm at the ultimate point. e double-modi ed Kessler and 4-strand Savage repairs performed with 3-0 suture failed by suture pullout, rupture or a combination of both with a mean gap of 5.6 mm and 5.4 mm, respectively, at the ultimate point.

1.2. e number of strands (2K3 vs. 4K3, and 4S4 vs. 6S4)

Increasing the number of strands signi cantly improved the yield force (2K3 vs. 4K3 p < 0.001, 4S4 vs. 6S4 p < 0.01), sti ness (2K3 vs. 4K3 p < 0.05, 4S4 vs. 6S4 p < 0.001), ultimate force (2K3 vs. 4K3, 4S4 vs. 6S4 p < 0.001), and all gap forces (2K3 vs. 4K3 p < 0.001, 4S4 vs. 6S4 at partial 3 mm p < 0.01, at all other gap points p < 0.001) (Fig. 17 and 18) (Table 4). In the modi ed Kessler con guration (2K3 vs. 4K3) the strain at the yield point increased (p < 0.01) and the strain at the ultimate point decreased (p < 0.05) along with the number of strands, but no di erences in strain were seen in the Savage con guration (4S4 vs. 6S4).

1.3. e suture calibre (4S4 vs. 4S3)

Increasing the suture calibre from 4-0 to 3-0 in the 4-strand Savage repair did not in uence the yield force, sti ness or partial gap forces, but it increased signi cantly the total gap forces (at total 1 mm p < 0.01, at total 2 and 3 mm p < 0.001) and the ultimate force (p < 0.01) (Fig. 17 and 18) (Table 4). e strain at the yield point decreased (p < 0.05), and the strain at the ultimate point increased (p < 0.01).

1.4. e suture con guration (4K3 vs. 4S3)

e suture con guration did not in uence the yield force, sti ness, ultimate force or gap forces of the repairs (Fig. 17 and 18) (Table 4). e strain at the yield point was signi cantly lower in the 4S3 than 4K3 repair. e strain at the ultimate point was not signi cantly in uenced by suture con guration.

63

2K3 4K3 4S3 4S4 6S4

Load

(N)

20

40

60

80

0

100

p < 0.01

p < 0.001p < 0.01p < 0.001

p < 0.001

F . e yield force and the ultimate force improved as the number of strands increased in the modi ed Kessler (2K3 vs. 4K3) and Savage repairs (4S4 vs. 6S4). e ultimate force increased with thicker suture calibre (4S4 vs. 4S3). e suture con guration did not in uence the forces. Mean (95% con dence interval).

= first linear force

= yield force

= ultimate force

T . Mean (95% con dence interval) strains (mm/mm), forces (N), and sti ness (N/mm)

Repair SFL SY SU FFL FY FU Stif

2K3 0.03 0.10 0.52 3.8 25.5 34.9 9.5 (0.01-0.10) (0.07-0.14) (0.40-0.65) (1.6-5.9) (21.6-29.4) (31.2-38.5) (7.9-11.2)

4K3 0.04 0.17 0.37 5.7 47.8 67.7 11.7 (0.02-0.06) (0.14-0.20) (0.29-0.44) (3.3-8.2) (40.2-55.5) (62.6-73.9) (10.5-13.0)

4S3 0.03 0.13 0.28 4.4 44.9 68.3 12.5 (0.01-0.05) (0.11-0.15) (0.23-0.33) (2.0-6.8) (38.9-50.9) (62.8-73.8) (10.9-14.1)

4S4 0.05 0.16 0.20 7.9 50.1 55.8 11.4 (0.03-0.07) (0.13-0.19) (0.17-0.23) (5.3-10.4) (44.1-56.1) (51.5-60.1) (10.4-12.3)

6S4 0.04 0.14 0.20 9.1 63.1 75.7 16.7 (0.03-0.05) (0.12-0.15) (0.17-0.23) (8.3-9.9) (55.3-70.8) (71.8-79.6) (15.9-17.4)

SFL = strain at rst linear point, SY = strain at yield point, SU = strain at ultimate point, FFL = rst linear force, FY = yield force, FU = ultimate force, Stif = sti ness.

R

64 R

F . e mean load-deformation curves of the repairs investigated with static tensile testing in Studies I, III, and IV. Repair techniques: (2K3) modi ed Kessler, (4K3) double modi ed Kessler, (4S3) 4-strand Savage, (4S4) 4-strand Savage, (6S4) 6-strand Savage, (3S) triple-stranded suture repair, (3SB) triple-stranded bound suture repair, (PLDLA) PLDLA repair.

65

F . In all repairs partial 1 mm gap opening occurred in the proximity of the yield point. Partial gapping preceded total gap formation. Mode of core suture failure was determined by suture calibre. e repairs performed with 4-0 suture failed at the ultimate point by sudden rupture of the strands before reaching total gap formation. e 3-0 suture repairs failed by suture rupture or pullout through the tendon with a gap of several millimetres by the ultimate force.

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66

. M PLDLA / (T ®) (II)

2.1. Biomechanical properties of the suture materials

e results of the tensile testing of the coated braided polyester suture (Ticron®) are presented in Table 5 and Fig. 19A. Knotting the suture strand with the USP simple knot signi cantly decreased the sti ness, and force and strain at the yield point and at the ultimate point (p < 0.001) distracted both at 70 mm/min and at 20 mm/min.

e higher distraction rate (20 mm/min vs. 70 mm/min) decreased signi cantly the ultimate force (p < 0.05) and strain at the ultimate point (p < 0.01) of the unknotted strands. No signi cant di erences existed between the simple knot strands distracted at 20 mm/min or at 70 mm/min.

e results of tensile testing of PLDLA suture are presented in Table 5 and Fig. 19B. e USP simple knot decreased signi cantly the sti ness, strain at the yield point, and strain and force at the ultimate point of the suture material compared to the unknotted strand (p < 0.001) when distracted both at 70 mm/min and at 20 mm/min.

e higher distraction rate (20 mm/min vs. 70 mm/min) increased signi cantly the yield force and ultimate force (p < 0.05), and strain at the ultimate point (p < 0.01) values of the unknotted strands, and the yield force (p < 0.01) and strain at the yield point (p < 0.001) values of the simple knot strands.

R

F . e results of the unknotted suture strand, suture strand with the standardized USP simple knot, and the best surgical knot con guration from biomechanical testing of coated braided polyester (A) and PLDLA 96/4 (B) sutures with a distraction rate of 20 mm/min. Knotting decreased the biomechanical properties of both materials. e PLDLA 1=1=1 knot approached the biomechanical properties of the PLDLA USP knot indicating good knot holding capacity, while the best coated braided polyester knot did not reach the biomechanical properties of the USP knot. ◊ = yield point, = ultimate point.

A. Coated braided polyester (Ticron®) B. PLDLA 96/4

67R

T . Coated braided polyester (Ticron®) and PLDLA sutures. Material properties presented as mean (95 % con dence interval) strain (mm/mm), force (N), and sti ness (N/mm) values of biomechanical testing at distraction rates of 70 mm/min and 20 mm/min.

C SFL SY SU FFL FY FU Stif

Unknotted 70 0.00 0.17 0.20 0.4 25.0 26.0 4.5 (0.00-0.00) (0.16-0.18) (0.20-0.21) (0.3-0.5) (24.7-25.3) (25.7-26.2) (4.4-4.7)

* *** *** *** *** ***Simple knotted 70 0.01 0.15 0.15 0.2 18.6 18.6 3.8 (0.01-0.01) (0.14-0.15) (0.14-0.15) (0.2-0.3) (18.0-19.2) (18.0-19.2) (3.6-4.0)

Unknotted 20 0.00 0.18 0.27 0.3 24.8 28.2 4.2 (0.00-0.00) (0.17-0.18) (0.26-0.27) (0.2-0.3) (24.6-25.1) (27.9-28.4) (4.1-4.4)

** *** *** *** *** ***Simple knotted 20 0.01 0.15 0.15 0.3 19.0 19.0 3.7 (0.0-0.01) (0.15-0.16) (0.15-0.16) (0.3-0.4) (18.4-19.5) (18.4-19.5) (3.5-3.9)

PLDLA SFL SY SU FFL FY FU Stif

Unknotted 70 0.00 0.04 0.44 0.3 11.1 28.6 8.9 (0.00-0.00) (0.04-0.04) (0.41-0.46) (0.2-0.4) (10.6-11.6) (27.2-29.9) (8.5-9.4)

*** *** *** *** ***Simple knotted 70 0.01 0.09 0.30 0.3 10.9 17.8 4.5 (0.01-0.01) (0.08-0.09) (0.27-0.33) (0.3-0.4) (10.7-11.0) (16.7-18.9) (4.2-4.7)

Unknotted 20 0.00 0.04 0.39 0.2 10.4 26.4 8.9 (0.00-0.01) (0.04-0.04) (0.37-0.41) (0.2-0.2) (10.1-10.7) (25.4-27.4) (8.4-9.5)

*** *** *** ***Simple knotted 20 0.00 0.07 0.28 0.3 10.0 16.7 4.7 (0.00-0.01) (0.07-0.07) (0.25-0.30) (0.2-0.4) (9.6-10.5) (15.7-17.6) (4.4-5.0)

SFL = strain at rst linear point, SY = strain at yield point, SU = strain at ultimate point, FFL = rst linear force, FY = yield force, FU = ultimate force, Stif = sti ness. Signi cant di erences between the unknotted and simple knotted strands are marked. *) p < 0.05, **) p < 0.01, ***) p < 0.001.

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T . Coated braided polyester (Ticron®) knot con gurations. Results of biomechanical testing at a distraction rate of 20 mm/min are presented as mean (95% con dence interval) strain (mm/mm), force (N), knot holding capacity (N), and sti ness (N/mm) values. e other knot con gurations were compared to the 1=1=1=1=1 knot (grey background). e values di ering signi cantly are presented with bold numbers.

Knots SFL SY SU SKHC FFL FY FU KHC Stif

F

1=1=1=1 0.01 0.18 0.36 0.19 0.3 11.2 13.9 11.8 1.9 (0.01-0.01) (0.13-0.23) (0.23-0.59) (0.14-0.24) (0.2-0.4) (9.0-13.4) (12.6-15.2) (9.3-14.3) (1.6-2.1)

1=2=1 0.01 0.10 0.38 0.10 0.3 8.2 14.3 8.2 2.6 (0.01-0.01) (0.08-0.12) (0.32-0.43) (0.08-0.12) (0.2-0.4) (6.7-9.6) (13.4-15.2) (6.7-9.6) (2.4-2.8)

2=1=1 0.01 0.12 0.32 0.10 0.2 7.1 10.3 7.2 1.8 (0.01-0.01) (0.10-0.15) (0.19-0.45) (0.06-0.14) (0.1-0.2) (5.5-8.8) (8.3-12.3) (5.6-8.8) (1.6-2.1)

2=2 0.05 0.13 0.35 0.13 0.9 4.5 10.1 4.5 1.2 (0.03-0.08) (0.10-0.16) (0.28-0.43) (0.10-0.16) (0.5-1.2) (3.4-5.5) (7.4-12.8) (3.4-5.5) (0.9-1.5)

2x2 0.00 0.13 0.23 0.11 0.2 7.6 9.8 6.7 1.5 (0.00-0.00) (0.09-0.18) (0.18-0.28) (0.08-0.14) (0.1-0.2) (4.6-10.6) (7.5-12.0) (4.1-9.2) (1.2-1.9)

F

1=1=1=1=1 0.01 0.22 0.23 0.22 0.3 17.8 18.1 17.8 2.5 (0.01-0.01) (0.21-0.24) (0.22-0.24) (0.21-0.24) (0.3-0.4) (16.7-19.0) (17.4-18.8) (16.7-19.0) (2.0-3.0)

1=2=1=1 0.01 0.25 0.25 0.25 0.4 17.4 17.4 17.4 2.4 (0.01-0.01) (0.23-0.27) (0.23-0.27) (0.23-0.27) (0.3-0.4) (16.8-17.9) (16.8-17.9) (16.8-17.9) (2.2-2.5)

2=1=1=1 0.00 0.23 0.24 0.24 0.3 16.5 16.7 16.5 2.1 (0.00-0.01) (0.21-0.26) (0.22-0.26) (0.22-0.26) (0.2-0.3) (15.1-17.9) (15.4-18.0) (15.1-17.9) (1.8-2.3)

S

1=1=1=1=1=1 0.00 0.21 0.21 0.21 0.3 17.2 17.4 17.4 2.2 (0.00-0.01) (0.20-0.21) (0.20-0.22) (0.20-0.22) (0.3-0.4) (16.7-17.7) (17.0-17.7) (17.0-17.7) (2.1-2.3)

SFL = strain at rst linear point, SY = strain at yield point, SU = strain at ultimate point, SKHC = strain at KHC, FFL = rst linear force, FY = yield force, FU = ultimate force, KHC = knot holding capacity, Stif = sti ness.

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2.2. Biomechanical knot properties

e results of the biomechanical testing of the Ticron® knots are presented in Table 6. e 1=1=1=1=1 knot con guration has been statistically compared to the other knots, and the values di ering signi cantly (p < 0.05 or less) are presented with bold numbers. All four throw con gurations slipped with increasing load. Of the ve throw con gurations, the 1=1=1=1=1 knot reached the best biomechanical properties but did not reach the properties of the USP simple knot (Fig. 19A) (Table 5). Adding the sixth throw did not improve the biomechanical properties.

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T . PLDLA knot con gurations. Results of biomechanical testing at a distraction rate of 20 mm/min are presented as mean (95% con dence interval) strain (mm/mm), force (N), knot holding capacity (N), and sti ness (N/mm) values. e other knot con gurations were compared to the 1=1 knot (grey background). e values di ering signi cantly are presented with bold numbers.

Knots SFL SY SU SKHC FFL FY FU KHC Stif

T

1=1 0.02 0.11 0.33 0.32 0.5 9.8 16.7 16.7 4.2 (0.01-0.04) (0.08-0.14) (0.30-0.36) (0.29-0.35) (0.2-0.9) (9.1-10.5) (15.5-18.0) (15.4-18.0) (3.2-5.2)

1x1 0.01 0.05 0.17 0.06 0.2 2.0 4.6 2.7 1.5 (0.00-0.01) (0.03-0.07) (0.09-0.25) (0.04-0.09) (0.1-0.2) (1.5-2.5) (3.7-5.4) (1.6-3.9) (0.9-2.1)

T

1=1=1 0.01 0.06 0.30 0.30 0.3 9.1 16.8 16.8 5.3 (0.00-0.01) (0.06-0.07) (0.27-0.33) (0.27-0.33) (0.2-0.3) (8.2-9.6) (15.2-18.3) (15.2-18.3) (4.8-5.7)

1=2 0.01 0.08 0.31 0.31 0.2 8.4 14.9 14.9 3.9 (0.00-0.01) (0.07-0.09) (0.28-0.33) (0.28-0.33) (0.2-0.3) (7.7-9.0) (13.9-15.9) (13.9-15.9) (3.5-4.3)

2=1 0.01 0.09 0.34 0.34 0.3 8.7 15.4 15.4 3.3 (0.00-0.02) (0.07-0.11) (0.30-0.38) (0.30-0.38) (0.2-0.3) (8.1-9.3) (14.3-16.6) (14.3-16.6) (2.8-3.9)

1x1x1 0.01 0.08 0.32 0.30 0.2 9.1 15.4 15.4 3.6 (0.00-0.01) (0.07-0.09) (0.27-0.34) (0.27-0.34) (0.2-0.2) (8.8-9.4) (14.5-16.4) (14.5-16.4) (3.1-4.1)

1x2 0.01 0.07 0.32 0.32 0.3 7.8 15.7 15.7 3.6 (0.00-0.01) (0.06-0.09) (0.28-0.36) (0.28-0.36) (0.2-0.3) (6.3-9.2) (15.0-16.5) (15.0-16.5) (3.2-3.9)

2x1 0.00 0.03 0.24 0.04 0.2 2.0 7.3 2.6 1.5 (0.00-0.01) (0.02-0.04) (0.12-0.35) (0.03-0.06) (0.1-0.2) (1.3-2.7) (3.3-11.3) (1.5-3.7) (0.6-2.4)

SFL = strain at rst linear point, SY = strain at yield point, SU = strain at ultimate point, SKHC = strain at KHC, FFL = rst linear force, FY = yield force, FU = ultimate force, KHC = knot holding capacity, Stif = sti ness.

e results of the biomechanical testing of the PLDLA knots are presented in Table 7. e 1=1 knot con guration has been statistically compared to the other knots, and the values with signi cant di erences (p < 0.05 or less) are presented with bold numbers. e 1=1=1 knot con guration reached signi cantly better biomechanical properties compared to the 1=1 knot and approached the biomechanical properties of the USP simple knot (Fig. 19B) (Table 5).

e biomechanical properties of the PLDLA 1=1 and 1=1=1 knots and Ticron® 1=1=1=1=1 and 2=1=1=1 knots were compared. e sti ness of both PLDLA knots was signi cantly higher than that of the Ticron® knots (PLDLA 1=1=1 vs. Ticron® 2=1=1=1 and 1=1=1=1=1 p < 0.001; PLDLA 1=1 vs. Ticron® 2=1=1=1 p < 0.01 and 1=1=1=1=1 p < 0.05). e strain and force at the yield point were signi cantly higher in the Ticron® knots compared to the PLDLA knots (p < 0.001). e ultimate force and KHC of the compared knots did not di er signi cantly. e strain at the ultimate point and the SKHC of the PLDLA knots were signi cantly higher than those of the Ticron® knots (p < 0.01).

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2.3. Morphometrical analysis of the secure knots

e size of the 1=1=1=1=1 and 2=1=1=1 Ticron® knots did not di er signi cantly in the morphometric analysis. ere was no di erence in the size of the two PLDLA knots either (1=1 and 1=1=1) (Table 8). e size of both PLDLA knots was signi cantly smaller than those of the polyester knots (p < 0.001).

T . Mean (95% con dence interval) strain (mm/mm), force (N), and sti ness (N/mm) values of the 6-strand modi ed Kessler repairs performed with triple-stranded suture or triple-stranded bound suture.

Suture SFL SY SU FFL FY FU Stif

3S 0.01 0.15 0.29 1.7 43.8 52.8 10.3 (0.00-0.02) (0.13-0.17) (0.23-0.35) (0.6-2.8) (38.3-49.2) (44.9-60.7) (9.2-11.4)

3SB 0.01 0.18 0.37 2.0 55.6 65.9 10.8 (0.01-0.02) (0.16-0.20) (0.26-0.48) (1.0-3.0) (50.7-60.5) (60.0-71.8) (9.9-11.8)

3S = triple-stranded suture, 3SB = triple-stranded bound suture. SFL = strain at rst linear point, SY = strain at yield point, SU = strain at ultimate point, FFL = rst linear force, FY = yield force, FU = ultimate force, Stif = sti ness.

. T - - P K (III)

3.1. Width of the sutures

ere was no signi cant di erence between the mean width of the triple-stranded 797 µm (788-806 µm) and triple-stranded bound sutures 801 µm (791-811 µm).

3.2. Mode of failure of the repairs

In all repairs failure of the peripheral suture near the yield point initiated partial gap formation which preceded total gap formation (Fig. 18). All core sutures failed during total gap formation, as the suture loops pulled through the tendon bres.

3.3. Force, strain, and sti ness of the repairs

e 6-strand modi ed Kessler repair performed with the triple-stranded bound suture reached signi cantly higher yield force (p < 0.01), ultimate force (p < 0.01), and partial (p < 0.01) and total (1mm p < 0.01, 2 and 3 mm p < 0.05) gap force values compared to the triple-stranded suture (Table 9) (Figs. 18 and 20). e sti ness and strain values did not di er signi cantly.

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T . Morphometrical analysis of the knots presented as mean (95% con dence interval) area (mm2).

Ticron® Knot area PLDLA Knot area

2=1=1=1 3.5 (3.4-3.6) 1=1 2.7 (2.5-3.0) 1=1=1=1=1 3.7 (3.5-4.0) 1=1=1 3.0 (2.8-3.1)

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p < 0.01

p < 0.01

3S 3SB0

20

40

60

80

100Lo

ad(N

)

= first linear force

= yield force

= ultimate force

F 0. e yield force and ultimate force were signi cantly higher in the 6-strand modi ed Kessler repair performed with triple-stranded bound suture (3SB) compared to the triple-stranded suture (3S). Mean (95% con dence interval).

T . Mean (95% con dence interval) strain (mm/mm), force (N), and sti ness (N/mm) values of the 6-strand modi ed Kessler repair performed with PLDLA triple-stranded bound suture.

Suture SFL SY SU FFL FY FU Stif

PLDLA 0.03 0.25 0.30 3.8 76.8 82.3 11.4 (0.02-0.03) (0.23-0.28) (0.27-0.33) (2.8-4.8) (66.7-86.9) (73.4-91.3) (10.6-12.1)

SFL = strain at rst linear point, SY = strain at yield point, SU = strain at ultimate point, FFL = rst linear force, FY = yield force, FU = ultimate force, Stif = sti ness.

. B PLDLA / - P K (IV)

4.1. Mode of failure of the repairs

In static testing, the failure of the PLDLA repairs was initiated by the failure of the peripheral suture near the yield point (Fig. 18). e failure of the core suture occurred by pullout in ve and by rupture in ve of the PLDLA repairs. Also in cyclic testing rupture of the PLDLA and Savage repairs was initiated by the failure of the peripheral suture.

4.2. Static and cyclic testing

e results of static tensile testing of the PLDLA repair are presented in Table 10 and Fig. 18. e progressive failure of each PLDLA and Savage repair specimen during cyclic loading is

presented in Fig. 21. e PLDLA repair withstood signi cantly more Newton-cycles compared to the Savage repair at every gap point (Fig. 22). In both groups, extension was the highest during the rst one hundred cycles, during which the elongation of the PLDLA repair was higher; therea er the average extension curves followed a similar pro le (Fig. 23).

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F . e failure of each PLDLA and Savage repair specimen during cyclic loading. par = partial gap, tot = total gap.

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F . e PLDLA repair withstood signi cantly more Newton-cycles compared to the Savage repair at every gap point. Par = partial gap, Tot = total gap. Statistical signi cance: ** p < 0.01, *** p < 0.001.

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F . e average extension curves of the PLDLA and Savage repairs during cyclic testing. P = partial gap (mm), T= total gap (mm).

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DISCUSSION

e present experimental studies were conducted to develop a new strong, and yet simple exor tendon repair technique using the bioabsorbable PLDLA 96/4 material to withstand the

forces of postoperative early active mobilization. e porcine extensor digiti quarti proprius tendon was chosen as the tendon material for the tensile testing of the repair techniques due to its availability and size similar to that of the human FDP tendon (Boyer et al. 2001b). Porcine extensor tendons have also previously been used in experimental studies (Savage 1985). Although biomechanical and structural di erences may exist between human exor and porcine extensor tendons, the reported biomechanical properties of the modi ed locking Kessler and Savage repairs investigated in porcine extensor digiti quarti proprius tendons in the present study (I) and in a previous study (Savage 1985) correspond to human cadaver

exor tendon studies with similarly performed modi ed Kessler (Merrel et al. 2003) and Savage (Aoki et al. 1994) repairs.

e tendon repairs were subjected to static linear tensile testing (I, III, IV) which is the most commonly used method to evaluate and compare the biomechanical properties of di erent techniques, o ering a tool to study the strength and mode of failure under direct visualization of gap formation and minimizing other variables a ecting the repair strength (Goodman and Choueka 2005). Also dynamic testing, which o ers a tool to investigate the in uence of repetitive loading, thus simulating postoperative rehabilitation (Pruitt et al. 1991, Sanders et al. 1997, Barrie et al. 2000a, 2001, Wolfe et al. 2007), was used to further evaluate the biomechanical properties of the novel PLDLA triple-stranded bound suture repair technique (IV).

e tendon repair is considered to be a composite of the core and the peripheral sutures (Lotz et al. 1998, Merrel et al. 2003). To improve the strength of the intact tendon repair, di erent components of the repair need to be evaluated. Lotz et al. (1998) have previously demonstrated that an imbalance in load-sharing between the stronger core and the weaker peripheral suture exists in a repair composite of the modi ed Kessler and simple running peripheral suture. e weaker peripheral suture carried approximately 64-77% of the total load at the point of its rupture. Hence, in theory, the strength of the repair composite can be improved by optimizing the load sharing between the core and the peripheral sutures either by increasing the sti ness of the core suture or the strength of the peripheral suture (Lotz et al. 1998, Merrel et al. 2003). Previous biomechanical static tensile testing studies have usually focused on the failure region of the load deformation curve and have de ned the ultimate force considering it the strength of the repair (Table 1). However, at ultimate point the disruption of the repair has already started, and a gap of o en several millimetres already exists at the repair site (I) (Lotz et al. 1998, Dinopoulos et al. 2000). Only few studies have investigated the load deformation curve prior to gap formation (Diao et al. 1996, Gordon et al. 1998, Kubota et al. 1998, Lotz et al. 1998, Gordon et al. 1999, Wada et al. 2000, Tang et al. 2001b, Dona et al. 2004, Su et al. 2005a, Cao et al. 2006), and even fewer have evaluated the biomechanical in uence of a single variable in the core suture technique (Kubota et al. 1998, Wada et al. 2000, Dona et al. 2004, Cao et al. 2006). us, the rst objective of the present study was to investigate the in uence of the di erent structural properties of the core suture on the biomechanical properties and the mechanism of failure of a tendon repair. One variable at a time (the number of strands, suture con guration or suture calibre) was evaluated to de ne which factors can be used to improve the biomechanical properties of the repair composite (I).

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Previous investigators have reported failure of the peripheral suture before the core suture (Wade et al. 1986, Diao et al. 1996, Lotz et al. 1998, Barrie et al. 2000a). e present study showed that in all the repairs the failure of the peripheral suture occurred in the proximity of the yield point of the load deformation curve and triggered increasing gap formation at the repair site (I). us, the yield force can be considered the maximum strength of the intact repair composite. It can be assumed that if the repair should remain intact during rehabilitation, the forces subjected to the repair should not exceed the yield force of the repair. e present results also show that the biomechanical properties of the intact repair composite (i.e the linear region of the load-deformation curve) can be in uenced by varying the properties of the core suture.

Although several previous studies have reported increased ultimate force along with the number of strands, few studies have investigated the number of strands as the only variable (Aoki et al. 1995c, Shaieb and Singer 1997, Kubota et al. 1998, Smith and Evans 2001). Only Kubota et al. (1998) investigated the in uence of increasing the number of strands on the strength of the intact repair by de ning the sti ness of 2- and 4-strand modi ed Kessler repairs. However, the repairs did not include a peripheral suture (Table 1). In the present study (I), both with the Pennington modi ed Kessler and Savage core sutures the sti ness and yield force of the repair composites as well as gap forces during progressive repair failure increased signi cantly along with the number of strands. is may be due to the higher material strength, the improved holding capacity of the repair technique of the tendon, or both. In these modi ed Kessler and Savage techniques the material strength of the sutures increased linearly along with the number of strands, as the number of unknotted and knotted strands increased in the same relation. However, as the repairs were performed with single-stranded suture by making multiple similar but separate core sutures, also the number of suture grips of the tendon increased concomitantly along with the number of strands. Consequently, with a certain load subjected to the repaired tendon, the load per strand and per grip in the repair technique is reduced, which presumably improves the holding capacity of the repair technique of the tendon. is consideration is supported by a previous nding of Barrie et al. (2000a) who performed a comparative study increasing the number of strands from four to eight using single- or double-stranded sutures in the same con guration, thus not increasing the number of separate grips concomitantly. ey found that though the material strength increased, the results were controversial in regard to holding capacity, because no di erence was seen in the gap resistance, while the fatigue strength increased during cyclic loading. Hence, on the basis of the present results, in addition to the increased material strength, the enhanced holding capacity of the multiple grips is an essential factor in the improved biomechanical properties of multi-strand techniques performed with single-stranded suture.

e material strength of the repair can be increased by using a thicker suture calibre. Although several investigators have reported that in static tensile testing increasing the suture calibre has signi cantly improved the ultimate force (Mashadi and Amis 1991, Hatanaka and Manske 2000, Alavanja et al. 2005), the in uence on gap formation has been questionable (Hatanaka and Manske 2000, Alavanja et al. 2005); moreover, the e ect on sti ness has not been investigated. In the present study the sti ness, yield force, and partial 1, 2, and 3 mm gap forces were not improved with thicker suture calibre. However, total 1, 2, and 3 mm gap forces were signi cantly higher in the 3-0 suture than 4-0 suture repairs. With 4-0 suture failure occurred shortly a er the failure of the peripheral suture (Fig. 18; 4S4), as the total load was transferred onto the core suture which failed by suture rupture. With 3-0 suture the force still continued to increase during total gap formation (Fig. 18; 4S3) despite gradual suture pullout through

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the tendon bres. e failure occurred a er total 3 mm gap had formed either due to suture pullout or rupture indicating that the total strength of the four 3-0 coated braided polyester suture strands and the holding capacity of the grips of the Savage con guration were close to each other. Also other investigators have previously reported failure of 4-0 suture repairs predominantly by suture rupture (Barrie et al. 2000a, Choueka et al. 2000, Barrie et al. 2001, Taras et al. 2001, Xie et al. 2002, Dona et al. 2004, Xie et al. 2005, Cao et al. 2006,). us, the use of the stronger 3-0 suture o ers a margin of safety for material strength of the repair, but, in the light of the present results, it does not improve the strength of the intact repair composite.

When the material strength of the strands of the core suture is adequate, i.e. exceeds the mobilization forces subjected to the repaired tendon, the critical factor to the repair strength is the holding capacity of the grips of the tendon repair technique. Previously, several biomechanical studies have demonstrated that, compared to grasping loops, locking loops provide higher ultimate force (Hotokezaka and Manske 1997, Hatanaka and Manske 2000, Wada et al. 2000), gap force, and sti ness (Wada et al. 2000) (Table 1). ese improved biomechanical properties of the locking loops compared to grasping loops were seen only with 3-0 or thicker suture calibre (Hatanaka and Manske 2000, Taras et al. 2001). erefore, in the present study the biomechanical properties of the two di erent locking con gurations, the double Pennington modi ed Kessler and 4-strand Savage repairs, were investigated with 3-0 suture. It was found that in these techniques the four modi ed Kessler locking loops and four Savage cross-locks (two embedded and two exposed) in each tendon end were of equal holding capacity. is is in accordance with the result published later on by Xie and Tang (2005) who found no biomechanical di erences between the circle-locks and cross-locks in a 4-strand model (Table 1). e cross sectional area of the tendon encircled by the locking loops has been shown to in uence signi cantly the biomechanical properties of the tendon repair (Hatanaka and Manske 1999, Dona et al. 2004, Xie et al. 2005). In the present study each modi ed Kessler locking loop comprised 15% of the cross-sectional area of the tendon, which has previously been shown to optimize the biomechanical properties of the modi ed Kessler locking loop considering gap resistance (Hatanaka and Manske 1999). In addition, the 1.0 cm suture purchase used in the repairs has been shown to optimize the holding capacity of several 2- and 4-strand grasping and locking techniques (Tang et al. 2005, Cao et al. 2006).

us, further increase in the strength of the intact repair composite necessitates improving the holding capacity of the locking loops of the tendon with other means.

e present study (I) showed that increasing the strength of the core suture by using a thicker suture calibre did not in uence the sti ness, yield force or early gap forces. It also showed that the Savage con guration did not o er any biomechanical advantage over the locking modi ed Kessler con guration, while increasing the number of strands improved the strength of the intact repair composite but complicated the technical performance of the repair. us, the possibilities to improve the holding capacity of the tendon repair more simply with multiple concomitantly passed suture strands were investigated. As previously Barrie et al. (2000a) found that increasing the number of suture strands with a looped (double-stranded) suture did not improve the gap resistance of the non-locked and locked cruciate techniques, in the present study (III) two di erent triple-stranded sutures were developed, with the strands either remaining free (triple-stranded suture) or bound parallel to each other to form a ribbon-like structure (triple-stranded bound suture). e triple-stranded sutures were used in the Pennington modi ed Kessler con guration producing two di erent 6-strand repairs. All repairs failed by suture pullout in accordance with the increased material strength. Compared to the results with the Pennington modi ed Kessler repair performed with conventional single-

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stranded suture (I), the sti ness, yield force, all gap forces, and ultimate force of both these 6-strand modi ed Kessler repairs increased. Furthermore, the triple-stranded bound suture improved signi cantly the strength of the intact repair composite compared to the repairs performed with the triple-stranded suture. is is considered to be due to the at, ribbon-like structure of the triple-stranded bound suture, the only di erence between the two sutures, as the material strength of the triple-stranded suture and triple-stranded bound suture is virtually the same with the 7-0 polypropylene suture binding the 3-0 suture strands parallel in the triple-stranded bound suture and not participating in axial load bearing. e strain at the yield point was not increased in the repairs performed with triple-stranded bound suture indicating that the enhanced strength of the repair was not an artifact caused, for example, by delayed gap formation due to bunching of the tendon ends at the repair site. us, it is assumed that the improved biomechanical properties are due to the enhanced holding capacity of the locking loops of the tendon repair, provided by the triple-stranded bound suture. Keeping the three suture strands parallel side by side may contribute to the holding capacity of the locking loops through an increased contact area in the suture-tendon interface, thus preventing the sutures from cutting through the tendon bres.

e present study (II) also investigated the biomechanical material properties of the bioabsorbable PLDLA 96/4 suture to evaluate its suitability for exor tendon repair. Bioabsorbable suture materials have not been widely used in exor tendon repair in the hand due to insu cient tensile strength half-life and fear of increased tissue reaction and adhesion formation (Mashadi and Amis 1992a, Wada et al. 2001a). e PLDLA 96/4 mono lament suture has previously been investigated in vitro and in vivo in the rabbit demonstrating suitable tensile strength half-life and good biocompatibility considering exor tendon repair (Kangas et al. 2001, 2006). In vitro the tensile strength half-life of the 3-0 PLDLA 96/4 suture fell between ten and 13 weeks, and in subcutaneous implantation PLDLA sutures retained average 75% of the initial tensile strength at six weeks (Kangas et al. 2001). Implanted in the rabbit Achilles tendon, the suture demonstrated good biocompatibility with less tissue reaction compared to polyglyconate sutures (Maxon®) during a 12–week follow-up (Kangas et al. 2006). us, the PLDLA 96/4 suture has been considered a potential candidate for exor tendon repair (Kangas et al. 2001, 2006).

e coated braided polyester suture (Ticron®) was chosen as control in the biomechanical material testing, because it is widely used in exor tendon repair due to its good biomechanical and biocompatibility properties (Postlethwait et al. 1975, Postlethwait 1979, Mishra et al. 2003, Lawrence and Davis 2005). e coated braided polyester suture has earlier been shown to have a poor knot holding capacity. erefore three to ve throws per knot have been recommended (Holmlund 1974, Trail et al. 1989). In the present study all knot con gurations with four throws or fewer slipped with increasing load. e reason for the possible successful clinical use of the four throw knots with coated braided polyester sutures in exor tendon repair may be that the load subjected to the core suture strands during passive or dynamic rubberband traction rehabilitation remains low enough (about 9 N) (Schuind et al. 1992) not to cause signi cant slippage. If active rehabilitation is to be applied, the forces subjected to the repair increase (Schuind et al. 1992) and the knot holding capacity becomes more critical. All ve throw knot con gurations formed a secure knot, but also with ve throw knots care should be taken, because sliding knots were easily formed. e 1=1=1=1=1 knot reached the best biomechanical values and is thus recommended for use. e 2=1=1=1 knot may o er an advantage when tying under tension, because the rst double throw stays down better holding the tendon ends together; it is thus recommended as an alternative to the 1=1=1=1=1 knot.

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e PLDLA suture demonstrated good knot holding capacity, as several square and granny knot con gurations formed a secure knot. Even the 1=1 knot did not slip, but the 1=1=1 knot is recommended due to the higher sti ness and lower strain at the yield point.

In both materials, performing the USP standardized simple knot signi cantly decreased the sti ness and ultimate force compared to the unknotted strand. However, the yield force of the PLDLA suture was not in uenced by the simple knot, while the yield force of coated braided polyester suture decreased signi cantly. e standardized USP simple knot represents an ideal knot, as slippage of the knot is not possible, and can thus be used as a reference, when evaluating di erent surgical knot con gurations. In an ideal situation, the load deformation curve of the secure knot equals that of the USP simple knot. In the recommended Ticron® knots (1=1=1=1=1 and 2=1=1=1) especially the strain and sti ness values did not reach those of the simple knot. is is likely due to the adjustment or tightening of the multiple throws during loading. e best PLDLA knot (1=1=1) approached the biomechanical properties of the simple knot indicating a good knot holding capacity of the material. e sti ness of the unknotted PLDLA suture (8.9 N/mm) compared to Ticron® (4.5 N/mm) and also the sti ness of the secure PLDLA knot (1=1=1: 5.3 N/mm) compared to the secure Ticron® knot (1=1=1=1=1: 2.5 N/mm) were signi cantly higher. In PLDLA suture the yield point is reached earlier, a er which the sti ness of the suture decreases. However, the biomechanical properties of the unknotted and knotted PLDLA suture remain superior to Ticron® until the load-deformation curves of PLDLA and Ticron® sutures are crossed with loads of approximately 12-13 N both in the unknotted and the knotted strands (Fig. 19A and B). Previously, the needed strength of a repair to withstand active rehabilitation has been estimated to be approximately 50 N (Schuin et al. 1992, Strickland 1999). Distributed equally to the core suture strands in a 6-strand repair, a load of approximately 8-9 N only is carried by each suture strand. Furthermore, the peripheral suture carries part of the load contributing signi cantly to the strength of the repair composite (Lotz et al. 1998). us, with the level of loads subjected to each core suture strand, PLDLA suture demonstrates higher sti ness than Ticron®. e sti ness of PLDLA suture is also higher than previously reported for two other bioabsorbable sutures, the polyglyconate (Maxon®) and polydioxanone (PDS®) (Mäkelä et al. 2002). In tendon repair high sti ness of the core suture is considered an advantage, because it has been shown to increase repair gap resistance, possibly through improved load-sharing between the core and the peripheral sutures (Lotz et al. 1998, Mishra et al. 2003).

Although the diameter of the PLDLA suture was thicker compared to that of the 3-0 Ticron®, the smallest secure knots were signi cantly smaller. Even though it is not known to what extent suture material can be added between the tendon ends without interfering with the healing process, a smaller knot and, thus, less suture material is generally considered an advantage (Pruitt et al. 1996). It may also diminish the bulk of repair and the tendon gliding resistance, especially in multi-strand techniques with several knots (Zhao et al. 2001c).

As the biomechanical properties and knot properties of the PLDLA suture were found suitable for exor tendon repair (II) and in static tensile testing the Pennington modi ed Kessler repair performed with the novel triple-stranded bound suture of coated braided polyester suture reached the estimated forces needed to withstand active mobilization (III), the triple-stranded bound suture of the bioabsorbable PLDLA was developed and investigated in the Pennington modi ed Kessler repair (IV). Compared to the Pennington modi ed Kessler repair performed with the coated braided polyester triple-stranded bound suture (III), the PLDLA triple-stranded bound suture improved the yield force and gap resistance of the repair. Also

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compared to the 6-strand Savage repair (I), the yield force, partial gap forces, and ultimate force increased, while the sti ness remained lower. e yield force of the PLDLA repair exceeded the estimated forces of active mobilization (Schuind et al. 1992, Strickland 1999).

In accordance with previous studies (Pruitt et al. 1991, Barrie et al. 2000a), in dynamic testing gap formation initiated at signi cantly lower loads compared to static testing both in the PLDLA repair and the Savage repair. e elongation at each gap point, however, was similar in static and cyclic testing. It can be assumed that repetitive loading leads to fatigue of the repair composite and, thus, to gap formation and failure at loads lower than those seen in static load-to-failure testing. e PLDLA repair showed higher initial elongation compared to the Savage repair corresponding to its lower sti ness in static tensile testing. However, no correlation to the lower sti ness was found a er the initial period in cyclic testing, because therea er the elongation of both groups proceeded at the same rate. e PLDLA repair withstood signi cantly more Newton-cycles at every gap point compared to the Savage repair, which was originally developed for postoperative early active motion (Savage 1985) and later also used with succesful results (Savage and Risitano 1989). Consequently, also in cyclic tensile testing the biomechanical properties of the PLDLA repair reach the requirements for early active mobilization.

Broader, at suture instead of normal round suture is not a novel invention in surgery, but to the knowledge of the present author, it has not previously been investigated or used in

exor tendon repair in the hand. is type of suture material may o er several advantages also in exor tendon repair. e triple-stranded bound suture is easy to suture and produces a 6-strand repair with the technical performance, handling of the tendon, and time needed for a 2-strand repair. It also reduces the possibility of violating the suture strands compared with traditional multi-strand techniques, which require several subsequent needle passes. When the repair is performed with the triple-stranded bound suture, the strands are of the same length and tighten to the same tension. Hence, the subjected load is distributed equally onto each strand, preventing over-loading and rupture of single strands one by one, which is a common problem with traditional multi-strand techniques. In the locking loops the suture strands remain parallel, dividing the subjected load to a broader area on the tendon and thereby decreasing the tendency of the sutures to cut through the tendon tissue. In static tensile testing the yield force of the Pennington modi ed Kessler repair performed with the PLDLA triple-stranded bound suture exceeded the estimated forces of active mobilization, and in cyclic testing the repair demonstrated better gap resistance than the 6-strand Savage repair, one of the strongest traditional multi-strand techniques. us, the biomechanical properties of the PLDLA repair are promising considering early active rehabilitation a er exor tendon repair. Further investigations are still needed before clinical use can be considered: e biocompatibility of the PLDLA material in exor tendons with the tendon sheath is currently investigated in vivo. Also the in uence of the PLDLA triple-stranded bound suture on the gliding resistance of the tendon repair needs to be investigated in human cadaver exor tendons in situ.

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SUMMARY AND CONCLUSIONS

e present biomechanical tensile testing studies ex vivo were planned to develop a novel, strong, and yet simple bioabsorbable technique for exor tendon repair in the hand to meet the biomechanical requirements of early active mobilization.

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(I)Five core sutures which were modi cations of the Pennington modi ed Kessler and Savage con gurations were investigated with static tensile testing. e core techniques were the following: group 1) Pennington modi ed Kessler (3-0 coated braided polyester), 2) double Pennington modi ed Kessler (3-0), 3) 4-strand Savage (3-0), 4) 4-strand Savage (4-0), and 5) 6-strand Savage (4-0). All repairs included a simple running peripheral suture. e repairs were compared as paired in regard to one variable at a time to evaluate the in uence of the structural properties of the core suture – 1) the number of strands (groups 1 and 2 & groups 4 and 5), 2) suture con guration (groups 2 and 3), and 3) suture calibre (groups 3 and 4) – on the biomechanical properties of the intact repair composite and disruption of the repair. In all repairs visible failure was initiated by rupture of the peripheral suture in the proximity of the yield point of the load-deformation curve. Biomechanical di erences between the techniques were found already in the visually intact repairs during the linear region of the load-deformation curve. Increasing the number of strands signi cantly improved the sti ness and yield force as well as the gap forces and ultimate force both in the modi ed Kessler and Savage con gurations. e 4-strand Savage con guration demonstrated lower strain at the yield point, but did not di er from the double Pennington modi ed Kessler repair in other respects. Increasing the suture calibre in the 4-strand Savage technique improved the strain at the yield point but did not in uence the sti ness, yield force or partial gap forces. e total gap forces and ultimate force improved due to increased material strength, which led to gradual suture pullout with concomitantly increasing load. Ultimate failure of the 3-0 suture repairs occurred by suture pullout, rupture or a combination of both, while the 4-0 suture repairs tended to fail by suture rupture.

. M PLDLA /

(II) e biomechanical material and knot properties of the bioabsorbable PLDLA 96/4 suture

compared to the widely used coated braided polyester (Ticron®) suture were investigated using static tensile testing. e standardized USP simple knot decreased signi cantly the ultimate force and sti ness in both materials, and the yield force in Ticron® suture compared to the unknotted strands. e sti ness of both unknotted and USP simple knotted PLDLA suture was higher initially compared to Ticron® suture, but the yield point was achieved earlier leading to lower yield force and strain at the yield point. In Ticron® ve throws were needed to form a secure knot, with the 1=1=1=1=1 and 2=1=1=1 con gurations reaching the best biomechanical properties. In the PLDLA suture several granny and square knots formed a secure knot, but the 1=1=1 and 1=1 were the best and approached the

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biomechanical properties of the ideal knot, the USP standardized simple knot. ese PLDLA knots demonstrated higher sti ness than the recommended Ticron® knots, but the yield point was reached earlier. In the morphometrical analysis of the cross-sectional area of the recommended knots, the PLDLA knots demonstrated a signi cantly smaller size than the Ticron® knots.

. T - - P K (III)

e triple-stranded suture and triple-stranded bound suture were compared in the Pennington modi ed Kessler con guration to evaluate the in uence of triple-stranded sutures and the spatial arrangement of three concomitantly passing suture strands on the biomechanical properties of the repair in static tensile testing. In both groups all repairs failed by suture pullout, in accordance with the increased material strength. Compared to the Pennington modi ed Kessler repair with two strands (I) both 6-strand repairs reached higher yield force, gap resistance, and ultimate force. e triple-stranded bound suture improved the yield force (56 N), gap forces, and ultimate force of the Pennington modi ed Kessler repair signi cantly compared to the triple-stranded suture (yield force 44 N).

. B PLDLA / - P K (IV)e triple-stranded bound suture was made of the bioabsorbable PLDLA 96/4, and the

Pennington modi ed Kessler repair was performed and investigated with static and cyclic tensile testing. In static testing the PLDLA repair reached higher yield force (77 N), gap forces, and ultimate force compared to the repair performed with the triple-stranded bound suture of coated braided polyester (yield force 56 N) (III) and higher yield force, partial gap forces, and ultimate force compared to the 6-strand Savage (yield force 63 N) (I). In cyclic testing the PLDLA repair was compared to the 6-strand Savage repair with a staircase protocol with increasing load. e PLDLA repair showed higher initial elongation corresponding to its lower sti ness compared to the Savage repair (I) in static tensile testing. However, no correlation to the lower sti ness was found a er the initial period; therea er the elongation of both repairs proceeded at the same rate. e PLDLA repair withstood signi cantly more Newton-cycles at every gap point compared to the Savage repair. In both techniques gap formation was initiated at signi cantly lower loads in cyclic testing compared to static testing.

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1. e visible failure of the repair composite is initiated by the rupture of the peripheral suture which occurs in the proximity of the yield point of the load-deformation curve. us, the yield force can be considered the maximum strength of the visually intact repair composite.

The strength of the visually intact repair composite can be improved by changing the structural properties of the core suture. Increasing the number of strands and concomitantly the number of suture grips by performing multiple similar core sutures with single-stranded suture improves the biomechanical properties of the repair composite in the modi ed Kessler and Savage con gurations. e suture con guration and increasing suture calibre do not in uence the strength and sti ness of the repair composite in the studied techniques. To enhance further the strength of the repair composite consisting of the Pennington modi ed Kessler core suture and simple running peripheral suture requires increases in the holding capacity of the locking loops of the tendon.

2. e biomechanical properties of the PLDLA suture including knotted strands are suitable for exor tendon repair. With loads subjected to the core suture strands in the repair composite,

the elongation of PLDLA suture is lower compared to Ticron® suture which has commonly been used in exor tendon repair. e PLDLA suture has a good knot holding capacity, and a secure knot is achieved with fewer throws and smaller knot size (1=1=1 or 1=1) than in Ticron® suture (1=1=1=1=1 or 2=1=1=1).

3. e strength of the tendon repair composite consisting of the Pennington modi ed Kessler core and simple running peripheral suture can be increased with the coated braided polyester triple-stranded suture and further with the triple-stranded bound suture. e improved strength with the triple-stranded bound suture is considered a consequence of the enhanced holding capacity of the locking loops due to the increased tendon-suture interface, which distributes the subjected load to a broader area on the tendon, thereby decreasing the tendency of the sutures to pull out through the tendon tissue.

4. e strength of the Pennington modi ed Kessler repair performed with the PLDLA triple-stranded bound suture and simple running peripheral suture exceeded that of the repair performed with coated braided polyester triple-stranded bound suture (III) in static testing and the 6-strand Savage repair in static (I) and cyclic testing (IV). e results suggest that the Pennington modi ed Kessler repair performed with PLDLA triple-stranded bound suture is strong enough to withstand the forces of early active mobilization.

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ACKNOWLEDGEMENTS

e present study was carried out at the Department of Hand Surgery and Department of Orthopaedics and Traumatology, Helsinki University Central Hospital, University of Helsinki, and at the Institute of Biomaterials, Tampere University of Technology.

I wish to express my most sincere gratitude to my supervisor, Professor Emeritus Pentti Rokkanen, M.D., Ph.D., (Hon. Vet. Med.), the former Head and Surgeon-in-Chief of the Department of Orthopaedics and Traumatology, Helsinki University Central Hospital. I am deeply grateful to him for giving me the possibility to carry out this study and for his guidance, patience, and encouragement throughout its course. I will miss our regular meetings with discussions concerning scienti c problems as well as the events and wonders of everyday life.

I wish to thank my supervisor and teacher, Docent Timo Raatikainen, M.D., Ph.D., the Head of the Department of Hand Surgery, Helsinki University Central Hospital, for his encouragement during this study and for generously arranging me time o from the clinical work for bringing this thesis into its end.

I am deeply grateful to my teacher and co-worker Harry Göransson, M.D., Ph.D., the Assistant Head of the Department of Hand Surgery and Microsurgery, Tampere University Hospital. He suggested the topic to me and participated in the biomechanical testing and analysis of the tendon repairs as well as revising the manuscripts. His enthusiasm and encouragement, as well as criticism, have been irreplaceable.

I wish to thank Professor Minna Kellomäki, Dr.Tech. and Academy Professor Pertti Törmälä, Ph.D., B.M.S., M.D.Sci.h.c., Institute of Biomaterials, Tampere University of Technology, for providing excellent facilities for performing this study and for their expertise in biomechanical material testing and polymer technology.

I owe my special thanks to my co-worker Katja Huovinen, M.Sc., Institute of Biomaterials, Tampere University of Technology, who made an enormous work preparing all the polylactide sutures for the study. We have shared numerous interesting and joyful biomechanical testing marathons together.

I also wish to thank Mrs. Mia Kalervo, the former secretary of our research group, for her help in the o ce work, Mrs. Svetlana Solovieva, Ph.D., and Docent Teppo Järvinen, M.D., Ph.D., for their help with the statistics, and Mrs. Ilona Pihlman, L.F.Ph., for revising the English language.

Appointed by the Faculty of Medicine, University of Helsinki, Docent Martti Vastamäki, M.D., Ph.D., and Docent E. Antero Mäkelä, M.D., Ph.D., read the manuscript. I wish to thank them for their prompt review, advice, and expertise.

I owe my sincere gratitude to Professor Jari Salo, M.D., Ph.D., for his interest in and supportive attitude towards this study as well as for his encouragement especially during the nal phases of the study.

Collectively, I wish to thank my colleagues at the Department of Hand Surgery, Helsinki University Central Hospital, for their support and understanding for the time I have been away

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from the clinical work because of this study project, as well as my colleagues in my previous workplace Jorvi Hospital, and all other colleagues and members of the research group who have shown interest in this study and encouraged me with their positive comments.

With all my heart I thank my close friend Suvi for her friendship and belief in me – for sharing all the good and the not-so-good moments through so many years.

My warmest thanks I owe to my family, my parents Tuula and Jukka, for their unconditional love and encouragement throughout my life, and my sister Katariina with her little boys who have brought so much joy to my life. With them I have had the place by the mountains to relax completely whenever I have needed.

And nally I owe my warmest gratitude to Jari for his love and encouragement which helped me bring this thesis to its conclusion, as well as for making some of the illustrations and the layout of this thesis for me.

is work has been nancially supported by the Finnish Society for Surgery of the Hand, the Academy of Finland, the Research Foundation for Orthopaedics and Traumatology in Finland, the Instrumentarium Science Foundation, and the Special Governmental Subsidy for Health Science Research of Helsinki University Central Hospital.

Helsinki, May 2008

Anna Viinikainen

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