03-06 Internal Fixation

Principles of Internal Principles of Internal FixationFixation

Loretta Bubenik, DVM, MSLoretta Bubenik, DVM, MS

Diplomate ACVSDiplomate ACVS

March 6, 2002March 6, 2002


• The Goals of fracture repair areThe Goals of fracture repair are

– Atraumatic techniqueAtraumatic technique– Good reductionGood reduction– Stable fixationStable fixation– Early return to full function****** Early return to full function******


• Open reduction Open reduction – Surgically exposure of the fracture site Surgically exposure of the fracture site – Implants placed internallyImplants placed internally

• Closed reductionClosed reduction– Fracture site is not openedFracture site is not opened– External fixation (casts, splints, etc.) External fixation (casts, splints, etc.) – Becoming more popular with advanced imagingBecoming more popular with advanced imaging


• Advantages of open reductionAdvantages of open reduction

– Provides rigid fixation with few complicationsProvides rigid fixation with few complications– Allows weight bearing during fracture Allows weight bearing during fracture

healinghealing•Health of the limb and joints Health of the limb and joints

• Increases the circulationIncreases the circulation

•Promotes healingPromotes healing

– Internally placed implants are hidden Internally placed implants are hidden •No extensive careNo extensive care


• Disadvantages of open reductionDisadvantages of open reduction

– InvasiveInvasive– Potential for slow healing Potential for slow healing – InfectionInfection– Longer procedureLonger procedure– Higher cost Higher cost


• Factures affecting fracture repairFactures affecting fracture repair

– Type of fracture (simple/comminuted)Type of fracture (simple/comminuted)– Anatomical area fracturedAnatomical area fractured

•ArticularArticular•Which limbWhich limb•Where on the boneWhere on the bone

– Extent of soft-tissue damageExtent of soft-tissue damage– Duration of the fractureDuration of the fracture


• Factures affecting fracture repairFactures affecting fracture repair

– Animal’s age, weight and temperamentAnimal’s age, weight and temperament– Owner’s finances and ability to provide Owner’s finances and ability to provide

aftercareaftercare– Equipment available Equipment available – Surgeon’s experience. Surgeon’s experience.

Tension

Bending

Rotation

Compression

Fracture Forces

Orthopedic WireOrthopedic Wire

• FlexibleFlexible

• Made of stainless Made of stainless steelsteel

• Generally used in Generally used in conjunction with conjunction with other forms of other forms of fixationfixation

Full

Cerclage

Inter-

fragmentaryTension

band

Hemi-

cerclage

• Tension band Tension band – Opposes tensile forcesOpposes tensile forces

• muscle / ligament muscle / ligament

– converts tensile forces converts tensile forces to compressive forcesto compressive forces

• Principles of full cerclage wire Principles of full cerclage wire placementplacement

– Fracture must be long obliqueFracture must be long oblique– Bone must be reconstructedBone must be reconstructed– Use the appropriate sizeUse the appropriate size– Never use a single cerclage wireNever use a single cerclage wire– Place wires ~ 1 cm apartPlace wires ~ 1 cm apart– Place wires ~ 0.5 cm from fracturePlace wires ~ 0.5 cm from fracture

WiresWires

• Principles of full cerclage wire Principles of full cerclage wire placementplacement

– Do not entrap soft tissuesDo not entrap soft tissues– Place perpendicular to bonePlace perpendicular to bone– Lock wire in place where it changes Lock wire in place where it changes

diameter (K-wire or notch)diameter (K-wire or notch)– Wires must be tightWires must be tight– Do not bend ends overDo not bend ends over

WiresWires

WiresWires

• Securing full cerclageSecuring full cerclage

– Twisted wiresTwisted wires•Wire holders/pliersWire holders/pliers

•Wire tightenersWire tighteners

– Single and double loop wiresSingle and double loop wires•Special tensioning device requiredSpecial tensioning device required

Good

Bad

• Other factsOther facts

– Bending the twistBending the twist– Cutting the twistCutting the twist– Twist vs loopsTwist vs loops– Shift in bone Shift in bone

diameterdiameter– Blood supplyBlood supply

WiresWires

Intramedullary (IM) PinsIntramedullary (IM) Pins

• Very resistant to bending forcesVery resistant to bending forces

• Require little equipment to placeRequire little equipment to place

• Easy to removeEasy to remove

• Do little damage to blood supply if Do little damage to blood supply if properly usedproperly used

• InexpensiveInexpensive

• Closed or open techniquesClosed or open techniques

• IM pins do not counteract IM pins do not counteract rotational forcesrotational forces– Use additional fixationUse additional fixation

• External fixator External fixator

• PlatePlate

• Cerclage wiresCerclage wires

– Provide endosteal contactProvide endosteal contact• Fill 70% of the bone diameterFill 70% of the bone diameter

• ““Stacked” pinsStacked” pins– Do not provide appreciable Do not provide appreciable

stabilitystability

• IM pins alone are IM pins alone are poorly suited for poorly suited for comminuted comminuted fracturesfractures

• They can’t withstand They can’t withstand axial forcesaxial forces

• Collapse and Collapse and instability will resultinstability will result

• Steinmann pins are Steinmann pins are most commonly most commonly usedused

• They pins vary in They pins vary in diameterdiameter– Proportional to Proportional to

strengthstrength

• Vary in point Vary in point morphologymorphology– ChiselChisel– TrocarTrocar– ThreadedThreaded

• IM pin insertionIM pin insertion

– Jacob’s chuckJacob’s chuck– Low speed drillLow speed drill– RetrogradeRetrograde– NormogradeNormograde

• Retrograde Insertion:Retrograde Insertion:– Pin inserted from Pin inserted from

fracture site and fracture site and driven through driven through epiphysisepiphysis

• Normograde Normograde insertioninsertion– Pin inserted at Pin inserted at

epiphysis and driven epiphysis and driven across fracture lineacross fracture line

FemurFemurRetro or

Normograde

Extend hip

Intertrochanteric fossa

Direct laterally

Over reduce

TibiaTibia

Intra-articular

Always Normograde

Countersink or cut short

HumerusHumerus

Retro or NormogradeRetro or Normograde

Exit or start distal to Exit or start distal to greater tubercle on greater tubercle on the lateral aspectthe lateral aspect

Direct into medial Direct into medial aspect of condyleaspect of condyle

RadiusRadius

Avoid IM pins in the Avoid IM pins in the radiusradius

Must go through a Must go through a jointjoint

Radius is ovalRadius is oval

Kirschner WiresKirschner Wires

• Small and elasticSmall and elastic

• Usually used as:Usually used as:– Transcortical pins Transcortical pins

(“skewer wires”)(“skewer wires”)– Pin and tension Pin and tension

band fixationband fixation– Cross pinningCross pinning

• Dynamic pinningDynamic pinning

Interlocking NailsInterlocking Nails

• Specialized IM pinSpecialized IM pin

• Locked in place with bone screwsLocked in place with bone screws

• Counteracts all fracture forcesCounteracts all fracture forces

• Can be used for fractures of the Can be used for fractures of the femur, tibia, and humerusfemur, tibia, and humerus

• Can be placed open or closedCan be placed open or closed

• Limited approachLimited approach


• 4, 4.7, 6, and 8 mm4, 4.7, 6, and 8 mm

• Various lengthsVarious lengths

• Screw holesScrew holes

– 2 proximal, 2 distal2 proximal, 2 distal– 1 proximal, 2 distal1 proximal, 2 distal– 2 proximal, 1 distal2 proximal, 1 distal– 1 proximal, 1 distal1 proximal, 1 distal


• A few specificsA few specifics– Chose the biggest nail possibleChose the biggest nail possible– Don’t place an empty hole at the Don’t place an empty hole at the

fracture sitefracture site– Place screws 2 cm away from fracturePlace screws 2 cm away from fracture– Try to use four screws totalTry to use four screws total– Use smaller screws for 6 and 8 mm nailsUse smaller screws for 6 and 8 mm nails– Can dynamize the fractureCan dynamize the fracture

ScrewsScrews• Cortical ScrewsCortical Screws

– More threads, low pitch, More threads, low pitch, thin threadthin thread

– Only Fully threadedOnly Fully threaded– Used for cortical boneUsed for cortical bone

• Cancellous ScrewsCancellous Screws– Less threads, steep Less threads, steep

pitch, wide threadpitch, wide thread– Fully and partially Fully and partially

threadedthreaded– Used in soft boneUsed in soft bone

ScrewsScrews

• Used to secure bone plates to boneUsed to secure bone plates to bone

• Used as primary means of fracture Used as primary means of fracture repair repair

• Used to hold fracture fragments in Used to hold fracture fragments in place place

• Used to compress fracture fragmentsUsed to compress fracture fragments

• Used to form prosthetic ligamentsUsed to form prosthetic ligaments

ScrewsScrews

• Positional screwsPositional screws

– Hold bone fragments in placeHold bone fragments in place– Do not provide compression Do not provide compression – Threads engage both near and far Threads engage both near and far

cortexcortex– Must be placed perpendicular to boneMust be placed perpendicular to bone

• if positioning small fragments if positioning small fragments

ScrewsScrews

• Lag principleLag principle

– Used to compress fracture fragmentsUsed to compress fracture fragments– Used to hold plates on bone Used to hold plates on bone – Threads only engage far cortexThreads only engage far cortex– Must be placed perpendicular to the boneMust be placed perpendicular to the bone– Can be accomplished with Can be accomplished with

•partially threaded screw partially threaded screw

• over drilling near cortexover drilling near cortex

ScrewsScrews

ScrewsScrews

• Lag principleLag principle

– Used for interfragmentary compression Used for interfragmentary compression – Used for primary fracture repairUsed for primary fracture repair

•Articular fracturesArticular fractures

•Sacroiliac luxationsSacroiliac luxations

ScrewsScrews

Do not over tighten the screw, this will cause stripping

and screw loosening

Bone PlatesBone Plates

• Necessary for many fracturesNecessary for many fractures

• Requires specialized equipment and Requires specialized equipment and trainingtraining

• Not readily available in many Not readily available in many practicespractices

• More expensive than pinningMore expensive than pinning

Bone PlatesBone Plates

• CounteractCounteract

– TensionTension– CompressionCompression– ShearShear– Bending Bending – Rotational forcesRotational forces

Bone plates should be placed on the Bone plates should be placed on the

tension side of the bonetension side of the bone

Tension side of the boneTension side of the bone

• FemurFemur– CraniolateralCraniolateral

• Tibia*Tibia*– CraniolateralCraniolateral

• HumerusHumerus– CraniolateralCraniolateral

• RadiusRadius– CranialCranial

• Unla*Unla*– CaudalCaudal

• Mandible*Mandible*– dorsaldorsal

Some are not plated on the tension side due to impracticality and added difficulty

Plates are stronger if load sharing Plates are stronger if load sharing

with the bone occurs with the bone occurs

Plates come in a wide variety of shapes and

sizes

PlatesPlates

• FunctionsFunctions

– NeutralizationNeutralization– CompressionCompression– ButtressButtress

NeutralizationNeutralization

• Plate protects primary Plate protects primary repair from weight-repair from weight-bearing forcesbearing forces

• The weight-bearing The weight-bearing load is shared by both load is shared by both the plate and the bonethe plate and the bone

CompressionCompression

• Mechanical compression Mechanical compression added to the fracture added to the fracture sitesite

• The weight-bearing load The weight-bearing load is shared by both the is shared by both the plate and the boneplate and the bone

• Primary bone healing Primary bone healing resultsresults

ButtressButtress

• Spans a gap to prevent Spans a gap to prevent collapse of a fracturecollapse of a fracture

• AllAll of the weight-of the weight-bearing forces are bearing forces are transmitted through transmitted through the platethe plate

PlatesPlates

• Plate placementPlate placement

– Reconstruct the boneReconstruct the bone– Contour plate Contour plate – Drill, measure, and tap screws (one by Drill, measure, and tap screws (one by

one)one)– Apply screws from the fracture site out, Apply screws from the fracture site out,

alternating bone fragmentsalternating bone fragments– Engage at least six cortices per a major Engage at least six cortices per a major

bone fragmentbone fragment•More for comminuted fractures if possibleMore for comminuted fractures if possible

PlatesPlates

• Dynamic compression platesDynamic compression plates

– Allows compression of major bone Allows compression of major bone fragmentsfragments•External compressionExternal compression

– Screws must be LOADED in order to get Screws must be LOADED in order to get compressioncompression

– Plate can function in compression, Plate can function in compression, neutralization, and as a buttress plate neutralization, and as a buttress plate depending on how the screws are applieddepending on how the screws are applied

1)1) Load Drill Guide:Load Drill Guide: Provides 1 mm Provides 1 mm compression, screws are placed eccentricallycompression, screws are placed eccentrically

2) 2) Neutral Drill GuideNeutral Drill Guide:: Places the drill hole Places the drill hole centrally, thus little displacement is provided.centrally, thus little displacement is provided.

LoadingLoading a screw in the DCP for compression a screw in the DCP for compression

Applying compression to a fractureApplying compression to a fracture

Plates-Rod constructsPlates-Rod constructs

• Used for comminuted fracture repairUsed for comminuted fracture repair

• Decreases bending stress on plateDecreases bending stress on plate

• Counteracts rotational and axial Counteracts rotational and axial forcesforces

• IM pin only needs to fill 30-40% of IM pin only needs to fill 30-40% of the canal diameterthe canal diameter

• Monocortical screws are o.k.Monocortical screws are o.k.– Make sure you engage enough corticesMake sure you engage enough cortices

Removing ImplantsRemoving Implants

• In general, it is recommended that In general, it is recommended that all orthopedic implants be removed all orthopedic implants be removed

• In practice, however, we rarely In practice, however, we rarely remove orthopedic implantsremove orthopedic implants


• Why don’t we remove themWhy don’t we remove them

– CostCost– Post-op confinement requiredPost-op confinement required– Traumatic surgeryTraumatic surgery– Anesthesia riskAnesthesia risk– Potential for refracturePotential for refracture


• When to recommend removalWhen to recommend removal

– Interferes with function Interferes with function – Loosening or Breakage Loosening or Breakage – InfectionInfection– Thermal conductionThermal conduction– Biological reaction to implantsBiological reaction to implants– Young dogs?????Young dogs?????


• Radiographs should document Radiographs should document healing prior to removalhealing prior to removal– Unless implant failureUnless implant failure

• Warn owners about potential for Warn owners about potential for bone breakagebone breakage– Cage rest required after plate removalCage rest required after plate removal

• Good idea to culture implantsGood idea to culture implants


• IM pins are easier to remove than platesIM pins are easier to remove than plates– Must leave pins long enoughMust leave pins long enough– Not the same refracture worryNot the same refracture worry

• Young dogs tend to over-grow the implants Young dogs tend to over-grow the implants and they are hard to removeand they are hard to remove

• Plates on the pelvis and humerus should be Plates on the pelvis and humerus should be left in place if not causing a problemleft in place if not causing a problem

Advantages of one over anotherAdvantages of one over another

• IM pins are cheaper than plates and IM pins are cheaper than plates and interfere with blood supply lessinterfere with blood supply less

• Little equipment is required for pin Little equipment is required for pin placementplacement

• IM pins can migrate, especially if IM pins can migrate, especially if motion is presentmotion is present


• IM pins must be combined with IM pins must be combined with another form of fixationanother form of fixation– Cross pins can be used as a primary Cross pins can be used as a primary

fracture repair in some instances fracture repair in some instances

• IM pins are not ideal for comminuted IM pins are not ideal for comminuted or transverse fractures (limits to or transverse fractures (limits to amendable fractures)amendable fractures)


• Interlocking nails counteract all fracture forces Interlocking nails counteract all fracture forces and may do it better than platesand may do it better than plates

• Interlocking nails do require a lot of equipment Interlocking nails do require a lot of equipment and some expertise to place them, but are and some expertise to place them, but are cheaper than platescheaper than plates

• Interlocking nails are limited by the type of Interlocking nails are limited by the type of fracture you can repair and the size of the fracture you can repair and the size of the animalanimal


• Plates counteract all fracture forcesPlates counteract all fracture forces

• Plates are versatile and can be Plates are versatile and can be applied to many fracture types and applied to many fracture types and animal sizesanimal sizes

• Plating requires some expertise and Plating requires some expertise and expensive equipmentexpensive equipment


• Plating requires an aggressive Plating requires an aggressive surgical approach in most instancessurgical approach in most instances

• Plates may interfere with blood Plates may interfere with blood supply more than any of the other supply more than any of the other implantsimplants– Clinically not a major problemClinically not a major problem


• Open approaches may delay fracture Open approaches may delay fracture healing and predispose to infectionhealing and predispose to infection– Plates/screwsPlates/screws– Interlocking nails Interlocking nails

• Closed approaches can be used withClosed approaches can be used with– IM pinsIM pins

•External fixatorExternal fixator

– Interlocking nails require a limited approachInterlocking nails require a limited approach


• Hidden implants allow early function Hidden implants allow early function with out hassle of extra carewith out hassle of extra care– Casts and ex-fixators have added careCasts and ex-fixators have added care

• Articular fractures generally require Articular fractures generally require open approaches and stable fixationopen approaches and stable fixation– Plates are more idealPlates are more ideal– Lag screws are used in many instancesLag screws are used in many instances

03-06 Internal Fixation

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