04-locked plate fixation – principle and applications

7/27/2019 04-Locked Plate Fixation Principle and Applications

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Locked plate fixationLocked plate fixationPrinciple and applicationsPrinciple and applications

Dr. Edmund WongDr. Edmund Wong16th CUHK16th CUHK--AADOAADO

ComprehensiveComprehensive BioskillBioskill Course on Fracture FixationCourse on Fracture Fixation

April 14April 14--16, 200716, 2007


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StabilityStabilityStability of fixation is crucial for bothStability of fixation is crucial for bothanatomical and biological fixationanatomical and biological fixation

Stability affords early motion to maintainStability affords early motion to maintain

articular surfaces and soft tissuesarticular surfaces and soft tissues


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Absolute StabilityAbsolute Stability Strain at fracture siteStrain at fracture site

must be less than 2%must be less than 2%for lamellar bone, 10%for lamellar bone, 10%for woven bonefor woven bone

Example compressionExample compression

platingplating

Lead to primary boneLead to primary bonehealinghealing


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Relative StabilityRelative Stability Based on controlled motionBased on controlled motion

More physiological; leads toMore physiological; leads tocallus formationcallus formation

Example buttress plating,Example buttress plating,IM nailingIM nailing


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Anatomic vs. Biologic FixationAnatomic vs. Biologic Fixation Anatomic fixationAnatomic fixation--

plate maintains the reductionplate maintains the reductionwith no motionwith no motion

primary healing (primary healing (endostealendostealhealing)healing)

Cutting cones, creepingCutting cones, creepingsubstitutionsubstitution

NO CALLUSNO CALLUS

Biologic fixationBiologic fixation-- plate bridges the fractureplate bridges the fracture

site and allows controlledsite and allows controlledmotionmotion

secondary healingsecondary healing HematomaHematoma,,

inflammation, fibrousinflammation, fibroustissue,tissue, remodellingremodellingandanddifferentiation ofdifferentiation ofmesenchymalmesenchymal stem cellsstem cellsto form new boneto form new bone

CALLUSCALLUS


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Achieving Stability: Overcoming theAchieving Stability: Overcoming the

Forces at the Plate Bone InterfaceForces at the Plate Bone Interface

Axial stress (tension and compression)Axial stress (tension and compression)

Shear stress at plate bone interfaceShear stress at plate bone interface

1. Axial Load

2. Bending Load

3. Torsion


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Stability by plate bone friction

Conventional Plate BiomechanicsConventional Plate Biomechanics


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Stability by plate bone friction


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Periosteal NecrosisPeriosteal Necrosis Plate/bone interfacePlate/bone interface

createscreates compartmentcompartmentunder the plateunder the plate

PeriostealPeriosteal necrosisnecrosis

LCLC--DCP plates onlyDCP plates onlyreduce contact by 50%reduce contact by 50%

Remember thatRemember that

plate/bone interfaceplate/bone interface

crucial for stabilitycrucial for stability


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Conventional PlateConventional Plate2.Movement of plate during axial loading

4.Causes screw to rotateAbout axis in distal cortex

3. Leading to high stress

and bone resorption

Axial

Load

1.Screw bending


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Conventional PlateConventional Plate

Bending Load

Force applied: screw orients to force. As

this occurs strength of fixation equals thread

pullout strength of single screw at the distal

or proximal end of the plate.

Force Axial


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Conventional PlateConventional PlateNote: screw plate angle change

Limits failure load to that to the

strength of thread purchase


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Limitations of Conventional PlatesLimitations of Conventional Plates

Failure in osteopenic boneFailure in osteopenic bone

GeriatricsGeriatrics

PeriostealPeriosteal avascularityavascularity

Tissue necrosis under plateTissue necrosis under plate Percutaneous platingPercutaneous plating

Plate elevated off of the bone. No friction betweenPlate elevated off of the bone. No friction between

plate and boneplate and bone


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Locking plate - Internal Fixator

Locking head screw

Threaded plate hole


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Internal Fixator


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Internal Fixator


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Internal Fixator


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Internal Fixator

Porotic bone


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Theoretical AdvantagesTheoretical Advantages No focal necrosis of bone and soft tissue deepNo focal necrosis of bone and soft tissue deep

to plateto plate improved local resistance to infectionimproved local resistance to infection

Avoids early temporary bone losses under plateAvoids early temporary bone losses under plateinduced by vascular damageinduced by vascular damage

Strength of fixation equals the sum of all theStrength of fixation equals the sum of all the

bolts (screws) ability to resist shear at the boltbolts (screws) ability to resist shear at the bolt--bone interface. Not that of a single screwbone interface. Not that of a single screwssthread purchasethread purchase


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Locking PlateLocking Plate

Plate does not have

to contact bone

Axial Load

As Single Beam Construct

Screws Must Shear Through Bone

Simultaneously


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Fixation fails when bolts

overcome bones resistanceto shear forces.

All bolts must fail as a single

construct.

Bolt plate interface allows no motion


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Screws with angularstability in different

directions


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Locking plate = internal external


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Locking plate = internal, external

Fixator

LongT

ub

e

LongP

late

Space

Spac

e

Space

Spac

e


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Biomechanical principles

similar to those of external fixators

Stress distribution


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Biomechanical principles

similar to those of external fixators

Stress concentration


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Advantages of int. Fixators

1. Angular Stability of Screws2. No accurate Plate Contouring

required3.Less Damage to Periosteum

4.Less Screw Loosening


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1. Angular Stability of Screws

LIFLC-DCP


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2. No accurate Plate Contouring required

LIFLC-DCP


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3. Less Damage to Periosteum

LIF

LC-DCP


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4. Less Screw Loosening

LIFLC-DCP


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ApplicationApplication


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LCPLCP

Locking Compression PlateLocking Compression Plate

Compression Plate andCompression Plate and


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Compression Plate andCompression Plate and

FixatorFixator


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LCP

Locking Compression Plate

CPLCP


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= DCP + Limited Contact + Locking Holes += DCP + Limited Contact + Locking Holes +TitaniumTitanium

Some designed for specific sites.Some designed for specific sites.

LCPLCP

Locking Compression PlateLocking Compression Plate

LCPLCP


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LCPLCP

Locking Compression PlateLocking Compression Plate Both aBoth a plateplate and anand an internalinternal fixatorfixator

Incorporating features of LCIncorporating features of LC--DCP (LimitedDCP (LimitedContact DCP)Contact DCP)

Used in MIPO, semiUsed in MIPO, semi--open or open fixationsopen or open fixations Uses nonUses non--locking and/or locking head screwslocking and/or locking head screws

(LHS)(LHS)

No externalNo external targettingtargetting devicedevice

Locking Screws


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Locking Screws

Self Taping & Self Drill ing

Self Taping

Metaph seal


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Metaphyseal

plate


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Pre-op planning XR

CT


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CT


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ReductionReduction TractionTraction

External fixationExternal fixation


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PrePre--contour of platecontour of plate


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Insertion of plateInsertion of plate


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Place another plate on the surface of skin can guide your

percutaneous skin incision for the locking screws.


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PrePre--contouredcontoured


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Locking plate

LISS


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LISS

Less Invasive Stabilisation System

LISSLISS


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LISSSS

Less InvasiveLess Invasive StabilisationStabilisation SystemSystem

A special kind ofA special kind of

LCPLCP

OutOut--rigger forrigger for

insertion andinsertion andtargettingtargetting

So far, only distalSo far, only distal

femur and proximalfemur and proximaltibiatibia


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LISSLISS


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Aiming device with guide sleeve for self-

drilling self-tapping screws (only in LISS)

Cooling required!

LISSLISS -- ReservationsReservations


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LISSLISS ReservationsReservations

Less InvasiveLess Invasive is surgeon / experienceis surgeon / experience

dependentdependent

Difficult to train / superviseDifficult to train / supervise Doubtful anatomical conformityDoubtful anatomical conformity

E.g.E.g. anteante--curvaturecurvature and size of the femoraland size of the femoralcondylecondyle

Not forgivingNot forgiving

Not adjustable / revisable once implantedNot adjustable / revisable once implanted


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Precaution:Precaution:

I t t!


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Important!

If the first screw to be inserted is a LockingHead Screw, it is important to ensure that the

plate shows good temporary fixation.

Otherwise, the plate rotates simultaneouslywhen locking the screw, and might cause soft-

tissue injuries

Locking Head ScrewsLocking Head Screws


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Locking Head ScrewsLocking Head Screws

Must be placed in exactMust be placed in exact

axial alignment with theaxial alignment with the

hole on the platehole on the plate

Difficult to angle screws inDifficult to angle screws in

plate to obtain osseousplate to obtain osseous

purchasepurchase

Drill blocks for selfDrill blocks for self--

tapping screws (requiringtapping screws (requiring

prepre--drill)drill)


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Should the plate lie too ventral or too dorsal, thescrews will not be centred in the medullary canal.

This position may compromise the screw purchase.


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Limited ability to compress fractureLimited ability to compress fracture


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Limited ability to compress fracturey p

Can not use plate as a reduction aidCan not use plate as a reduction aidPositioning and Compression Device

(PCD)


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Skin impingement


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Removal of locking screw from theRemoval of locking screw from the

plate sometimes is difficult:plate sometimes is difficult:need to prepare broken screwneed to prepare broken screw

removal setremoval set


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The EndThe End

Thank YouThank You

04-locked plate fixation – principle and applications

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