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J Shoulder Elbow Surg (2011) 20, 414-419

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Treatment of unstable distal clavicle fractures withKnowles pin

I-Ming Jou, MD, PhDa, Eric P. Chiang, MDb, Chii-Jen Lin, MD, PhDa,Cheng-Li Lin, MDa, Ping-Hui Wang, MDc, Wei-Ren Su, MDa,*

aDepartment of Orthopaedic Surgery, National Cheng Kung University Hospital, Tainan, TaiwanbDepartment of Anesthesiology and Critical Care Medicine, The George Washington University, Washington, DC, USAcDepartment of Orthopaedic Surgery, Chi-Mei Medical Center, Tainan County, Taiwan

Background: Unstable distal clavicle fractures often need surgical treatment. This report describes a newintramedullary extra-articular Knowles pin fixation method to treat these unstable fractures.Materials and methods: Twelve patients with unstable distal clavicle fractures (Neer type II) had surgerywith intramedullary extra-articular Knowles pin fixation. We retrospectively reviewed clinical results forpain, shoulder function, and range of motion, as well as radiographic results, for this institutional reviewboardeapproved study. Each patient’s operated arm was in a sling for 4 weeks postoperatively. The Univer-sity of California, Los Angeles shoulder rating scale score was used to evaluate shoulder function.Results: All patients showed radiographically confirmed bony union. The mean period required for heal-ing was 11.5 weeks, and patients were followed up for 6 to 24 months (mean, 15.2 months), during whichUniversity of California, Los Angeles scores (mean, 33.9) indicated good clinical results. Three patientshad the complication of proximal or distal skin irritation caused by the thread and hub of the Knowles pin.Conclusions: The Knowles pin fixation method is useful for treating unstable distal clavicle fractures.However, sufficient familiarity with the technique and careful preoperative planning to determine theappropriate length of the pin are necessary to prevent complications and to effect a high union rate.Level of evidence: Level IV, Case Series, Treatment Study.� 2011 Journal of Shoulder and Elbow Surgery Board of Trustees.

Keywords: Distal clavicle fracture; Knowles pin; Neer type II

Fractures of the clavicle are common, comprising about4% of adult fractures.17,18 Distal clavicle fractures accountfor approximately 21% of clavicle fractures.17,18 Distal-third clavicle fractures are rare and often result froma direct high-energy blow. Neer14 classified these fracturesinto 3 types according to the location of the

uests: Wei-Ren Su, MD, Department of Orthopaedic

al Cheng Kung University Hospital, 138 Sheng Li Road,

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ss: suwr@ms28.hinet.net (W.-R. Su).

ee front matter � 2011 Journal of Shoulder and Elbow Surgery

.2010.08.009

coracoclavicular (CC) ligament relative to the distal frag-ment. In Neer’s classification, type II fractures detachmedial fragments from the CC ligaments (Figure 1).Conservative methods for managing these fractures usuallylead to a high rate of nonunion. The delayed union ornonunion rate of conservative treatment is reported to be ashigh as 30%.10,14 Nonunion sometimes causes pain andimpaired function of the shoulder girdle and upper limb;thus, open reductioneinternal fixation is most often rec-ommended to treat this unstable injury.10,14,15 Because thedistal fragments are usually small or even comminuted, it is

Board of Trustees.

Figure 1 The Neer type II fractures of distal clavicle occur atthe level of the CC ligaments. The type II fracture is furtherdivided into type IIA, in which the fracture occurs medial to theCC ligament, and type IIB, in which the fracture occurs betweenthe CC ligament and is often associated with a torn conoidligament. Figure 2 The fracture was reduced and fixed with a Knowles

pin from the posterolateral aspect of the distal fragment to theanteromedial cortex of the proximal clavicle fragment.

Distal clavicle fractures 415

difficult to achieve secure fixation and early mobilization.Several methods of internal fixation have already beenproposed, including tension-band wiring,15 CC screwfixation,1 locking-plate fixation,9 and transarticular orextra-articular Kirschner wire fixation.4,14 Unfortunately,these methods have considerable risks for complications,specifically pin migration, loss of reduction, and acromio-clavicular (AC) joint degeneration. A hooked plate hasbeen developed to provide a more stable fixation and hasbecome more popular in recent years. However, hookedplating is not without significant complications, includingsubacromial impingement, acromial fracture, and rotatorcuff damage; thus, the hooked plate should be removed assoon as bony union is confirmed.10,13,21 Therefore, there isno current consensus regarding which method provides thebest clinical results.

Knowles pin fixation is recognized as a proven methodfor midshaft clavicle fractures,2,23 but it has not been usedfor distal clavicle fractures as an extra-articular intra-medullary fixation technique. The purpose of this retro-spective study was to report our experience using theKnowles pin to treat Neer type II distal clavicle fractures.

Materials and methods

After the study protocol was approved by the Human Experimentand Ethics Committee of National Cheng Kung University (ER-99-045), we retrospectively reviewed 12 patients (6 men and6 women) with unstable distal clavicle fractures who had surgerybetween August 2005 and July 2009. None of the patientsenrolled in our study had open fractures, pathologic fractures, orprevious surgeries on the affected clavicle or shoulder. Allsurgeries had been done by the same orthopaedic surgeon. Themean age of the patients at the time of surgery was 39.1 years(range, 12-61 years). The right shoulder was involved in 5 patientsand the left in 7 patients. The cause of injury was a motor vehicle

accident in 6 patients, a fall from a significant height in 3 patients,an athletic injury in 2 patients, and an auto-pedestrian accident in1 patient. The patients were evaluated by use of anteroposteriorradiographs of both shoulders that showed all 12 fractures to beextra-articular, localized to the distal third of the clavicle, andclassified as Neer type II. The length of the distal fragment wasmeasured on the radiographs as the distance from the lateral edgeof the clavicle to the medial edge of the distal fragment’s inferiorcortex.

The surgeries were completed with patients under generalanesthesia in the beach-chair position. First, a curved incision wasmade on the distal clavicle, and then dissection continued alongthe incision. An important technical issue was to minimizedisturbances to the CC ligament and AC joint capsule to preventdispersion of the likely comminuted fragments in the capsuleenvelope. The distal clavicle, along with the superior AC ligamentof the AC joint capsule and fracture site, was exposed. Theposterolateral margin of the distal clavicle close to the AC jointwas then confirmed.

The intramedullary canal of the medial fragment was pre-drilled toward the anteromedial cortex, with care taken not topenetrate the cortex. The distal fragment was then predrilled witha 2.5-mm drill bit that was directed parallel to the superior cortexand toward the posterolateral aspect of the distal fragment, with anexit point posterior to the AC joint. The lengths of both the distaland medial fragments were then measured to determine theappropriate length of the Knowles pin. A 3-mm suction tip wasinserted along the medullary tract of the distal fragment and exitedthrough the skin. A 3.8-mm Knowles pin was carefully insertedunder the guide of the suction tip through the distal fragment andinto the medial fragment after the fracture had been reduced. Toprevent the hub of the pin from irritating the overlying soft tissue,the pin was carefully advanced, with its hub pressed tightlyagainst the posterolateral cortex of the distal clavicle (Figure 2).The CC ligaments were not repaired. The AC joint was spared andremained intact throughout the procedure. The wound was irri-gated, and the soft tissue and skin were closed with appropriatesutures.

Figure 3 Patient 5, a 45-year-old man with a left Neer type II clavicle fracture caused by a motor vehicle accident. A, Upwarddisplacement of the medial segment was shown on the radiograph; the length of the distal fragment was 25.5 mm. B, Postoperativeradiograph after Knowles pin fixation with perfect reduction.

416 I.-M. Jou et al.

Each patient’s operated arm was in a sling for 4 weeks post-operatively. On the second postoperative day, gentle passivemovements and pendulum exercises were started, but overheadabduction was not permitted. The sling was removed after4 weeks, and patients were encouraged to actively mobilize thearm on the injured side without limitations on motion but still withsome restrictions on weight bearing.

We retrospectively reviewed the clinical and radiographicresults, and patients were evaluated for complications. Shouldersymptoms and functions were assessed under the University ofCalifornia, Los Angeles (UCLA) shoulder scoring system. Thesurgeon who carried out the operations also did the physicalexaminations and determined the UCLA scores. After osteosyn-thesis, plain radiographs were taken once every 3 to 4 weeks toevaluate the status of fixation in all patients. These radiographswere examined for bony union, implant failure, and pin migration.

Results

Twelve patients were followed up for a mean of 15.2 months(range, 6-24 months). Radiographically verified bony unionwas achieved in all patients, and themean period required forhealing was 11.5 weeks (range, 6-16 weeks). When bonyunion was achieved, the Knowles pin was removed (mean,13.8 weeks; range, 8-18 weeks) (Figure 3). The UCLAshoulder score showed good results in all patients (mean,33.9 points; range, 30-35 points) at the final follow-up. Allpatients’ shoulders recovered their full functional range ofmotion after 6 to 18 weeks. The mean length of the distalfragment was 28.5 mm (range, 25.5-34.1 mm) (Table I).

Irritation over the skin of the proximal clavicle bypenetration of the pin thread occurred in 1 patient, and skinirritation over the distal clavicle by the protruding hub of thepin occurred in 2 patients; all 3 were women with slenderfigures. However, all patients had full range of motion, noincidence of skin breakdown, and no reports of shoulderpain. The pin was removed after bony union was achieved,

and none of the patients had postoperative infection,nonunion, or osteoarthritic change to the AC joint.

Discussion

Clavicle fractures are common traumatic injuries thatcomprise 44% of shoulder girdle injuries.3,8 Surgicaltreatment is recommended for some displaced midshaftclavicle fractures and unstable distal clavicle fractures, andvarious operative procedures of clavicle fixation have beenintroduced. Intramedullary fixation of clavicles with Rushpins, K-wires, titanium elastic nails, and Knowles pins havebeen reported by several authors.5,6,22 To date, however, theoperative techniques have not been widely used because ofmigration of the intramedullary implants. Neer14 firstreported a transacromial method to treat clavicle fractureby fixation using K-wires. In 1990, Kona et al12 reviewed13 patients managed with Neer’s procedure and found6 nonunions and 5 deep infections. Smooth pin migrationinto the thoracic cavity may also be a lethal complication.Neviaser et al16 first introduced Knowles pin fixation foruse in midshaft clavicle fracture or nonunion. The resultswere excellent, and this technique proved to be thesimplest. In the previous study, the threaded Knowles pinwas superior to other intramedullary implants because pinmigration was avoided and fixation was enhanced. Theanterior threads of the pin can catch the proximal claviclecortices firmly to prevent lateral migration from loosening.Firm fixation of the anterior threads of the pin could alsoproduce interfragmentary compression, which in somecases results in penetration of the anteromedial cortex ofthe proximal clavicle. The posterior hub of the pin, whichtypically nestles behind the posterolateral corner of thedistal clavicle, can prevent medial migration of the pin.

Type II distal clavicle fractures occur medial to (typeIIA) or between (type IIB) the CC ligament.3,8,14 The CC

Table

IPresentationof12patients

treatedwithKnowlespin

fortypeII

fracture

ofdistalclavicle

from

2005to

2009

Patient

No.

Age

(y)

Gender

Sideof

injury

Mechanism

ofinjury

Evidence

of

unionon

radiography(w

k)

Functional

rangeof

motion(w

k)

Pin

removal

(wk)

Total

follow-up

(mo)

Length

of

distal

fragment(m

m)

Complication

UCLA

scales

156

FL

Motorvehicle

accident

10

10

12

10

27.8

34

212

ML

Athleticinjury

66

86

33.2

35

327

FR

Motorvehicle

accident

12

12

12

826.5

Skin

irritationby

protrudingpin

hub

35

425

MR

Fallfrom

height

10

812

12

34.1

34

545

ML

Motorvehicle

accident

12

12

16

18

25.5

35

623

FL

Motorvehicle

accident

10

12

14

12

25.8

35

751

FL

Pedestrianstruck

16

12

16

24

27.1

Skin

irritationby

penetrationofpin

thread

30

861

FL

Motorvehicle

accident

18

18

18

18

26.4

32

958

FL

Motorvehicle

accident

16

12

18

18

29.8

Skin

irritationby

protrudingpin

hub

32

10

33

MR

Athleticinjury

12

812

16

31.3

35

11

45

MR

Fallfrom

height

10

812

18

26.2

35

12

33

MR

Fallfrom

height

12

12

16

22

28.4

35

Distal clavicle fractures 417

ligament, consisting of the conoid and the trapezoid liga-ment, is considered the prime suspensory restraint of theAC joint against superior and posterior translation of thedistal clavicle. The loss of stability from the CC ligamentsresults in displacement superiorly, which is often associatedwith a high rate of nonunion and delayed union afterconservative treatment and thus requires surgical reductionand fixation for proper healing. Several surgical methodshave previously been reported for stabilizing this type IIunstable fracture, but the optimal method is yet to bedetermined. The use of Knowles pin fixation has beenrecognized as a proven method of treatment for midshaftclavicle fracture.2,16 Even though type II fractures areusually accompanied by small or comminuted distal frag-ments, application of the Knowles pin in type IIA and IIBfractures is still possible. There were some applications ofthe Knowles pin in the treatment of distal clavicle fracturesreported in the literature with variable results. Fann et al5

reported on 34 patients managed with transarticularKnowles pin; all patients had solid union and could returnto their previous work and activities without any functionaldisturbances. However, 1 AC arthrosis was found in thisseries, and to prevent arthrosis, early removal of thetransarticular Knowles pin after bony union was suggested.The complication of AC arthrosis might be anticipated tobe higher in the long-term follow-up if larger-diameterimplants are used. Furthermore, biomechanical studieshave confirmed that rotational movement occurs betweenthe clavicle and the scapula during shoulder motion. Anyinternal fixation that fixed the AC joint will interfere withthe normal biomechanical movement of the clavicle inrelation to the coracoid and acromion. Transacromial extra-articular Knowles pin fixation for Neer type II distal clav-icle fractures was reported by Wang and Wong22 withsatisfactory results; however, their technique was an indi-rect fixation method using the acromion and the proximalclavicle for fixation and required augmentation with Ethi-bond sutures (Ethicon, Somerville, NJ) between the prox-imal clavicle fragment and the coracoid process. Thisfixation method crossed the clavicle and acromion; thus,shoulder motion at the AC joint was limited. Therefore, allpatients had radiolucent zones around the pin, and 32% ofthe patients had lateral pin migration. AC joint osteoar-thritis might be anticipated in a long-term follow-up.

To our knowledge, there is no previous report in theliterature about intramedullary extra-articular Knowles pinfixation for distal clavicle fractures. Because the distalfragment is often small or even comminuted intra-articularly within the AC joint, secure fixation of thedistal fragment has been a chief concern. The stability ofthe distal clavicle fragment is maintained by the integratedfunctions of the deltoid fascia, the AC capsule, and theCC ligament. The mean distances from the medial edge ofthe footprint of the trapezoid and conoid to the articularsurface of the distal clavicle were 28.2 � 5.7 mm and49.7 � 5.4 mm, respectively.19 The mean length of the

418 I.-M. Jou et al.

distal clavicle fragment was 34 mm (range, 28-52 mm) inour series, which was greater than that of the medial edgeof the footprint of the trapezoid ligament. Furthermore,the CC distance from the most distal clavicle fragment tothe coracoid process was not increased preoperatively inour series. It appears that most of the fracture sites in ourseries were located medial to the insertion of the trapezoidligament. Therefore, the undamaged trapezoid ligament orconoid ligament could provide the essential stability forthe distal clavicle fragment. In addition, the AC capsu-loligament was attached to and around the distal fragmentof the clavicle. The mean distance from the distal clavicleto the medial end of the capsuloligamentous insertion wasabout 5.4 to 6.6 mm.20 All the locations of the distalclavicle fractures in our series were more medial thanthose distances. Although occasionally some of the distalclavicle fragment was comminuted and likely extendedwithin the insertion of the AC joint capsule, the ACcapsule could provide adequate stability for the distalfragment if it remained intact. An important aspect thatmade this procedure very practical was the adequateholding power of the CC ligament and AC capsu-loligamentous structure as long as they were intact. Theultimate load of the trapezoid ligament, conoid ligament,and AC ligament was 440 � 118 N, 394 � 170 N, and849 � 297 N, respectively.7 Once the trapezoid ligamentand AC capsule were intact, the sum of the ultimate loadwas greater than the mean failure load of the clavicle (732� 175 N).11 Therefore, the strength of the trapezoidligament and AC ligaments yields sufficient holdingpower to maintain the distal fragment of the claviclefracture and to secure reduction of the fracture under thefixation of the Knowles pin, as was done in the treatmentof the midshaft fracture.

Advantages of intramedullary extra-articular fixationinclude smaller incision, reduced need for dissection andsoft-tissue stripping, and relative protection of the supra-clavicular nerves. Other advantages include the ability toremove the implant with the patient under local anesthesiaand the load-sharing nature of the device. The Knowlespin has enough mechanical strength to withstand theforces generated across the fracture site during union thatthere is no implant failure in our series. From a biome-chanical point of view, intramedullary positioning of theimplant has many advantages in the treatment of claviclefractures. The position of the Knowles pin is extra-articular and can maintain the biomechanics of the ACjoint to allow a degree of early mobilization, thus avoid-ing the complications of impingement and stiffness.Neither were the CC ligaments reconstructed, nor wasthere a need to augment the fixation with wires or slingsaround the coracoid process. However, the determinationof the pin length was quite important during the appli-cation of this method. The length of the Knowles pinshould be appropriate to the point where it just contactsthe anteromedial cortex of proximal clavicle. If the length

of the pin is too great, the pin will advance too far, andthe skin of the proximal clavicle could be irritated bypenetration by the anterior threads before the hub nestlesto the cortex. In addition, the hub could be felt throughthe skin if it was not nestled up closely to the cortex. Ifthe length of the pin is too little, interfragmentarycompression cannot be achieved after the hub nestles tothe cortex. Nevertheless, potential drawbacks to thistechnique include the possibilities of hardware promi-nence, implant migration or breakage, or infection and theneed for hardware removal.

Our study is a small, retrospective cases series withinherent bias. A longer follow-up and larger series arenecessary. In this study, we report our experience treating12 acute distal clavicle fractures with Knowles pin fixation.Although this treatment method resulted in 100% fractureunion, with all patients regaining nearly full postoperativeshoulder range of motion and resolution of symptoms, wefound some incidences of postoperative complications.Three cases had skin irritation as a result of pin promi-nence. We did not notice any skin breakdown at the site ofeither the proximal end of the anterior threads or the distalend of the posterior hub.

Conclusion

Intramedullary fixation of distal clavicle fractures witha Knowles pin is a safe surgical technique that achievesprimary stability for practice with minimal earlycomplications. The pin seems to provide a stable holdingforce in a small distal clavicular fragment. This hasbeen achieved without disturbance to the AC joint,subacromial space, or rotator cuff. Therefore, it can beconsidered as an alternative in the treatment of unstablefractures of the distal clavicle.

Acknowledgment

The authors thank Florence Y. Ling, University of Col-orado at Boulder, for her help in the preparation of themanuscript.

Disclaimer

The authors, their immediate families, and any researchfoundations with which they are affiliated have notreceived any financial payments or other benefits fromany commercial entity related to the subject of thisarticle.

Distal clavicle fractures 419

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