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Why do we have bones

?

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Why do fractures heal

?

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Evolution

endoskeleton

genetic pool

reproduction

intramembranous v endochrondralossification

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Intramembranous Bone

Formation

occurs at periosteal surface

pelvis, scapula, clavicle, skull

osteoblasts form a calcified matrix withincollagen framework

everyday stress fractures

~ primitive process

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Endochondral Bone Formation

occurs at growth plates and within #callus

osteoblasts form osteoid on cartilagenousframework

fractures

~ mature process

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Fracture Treatment

reduce HoldRehabilitate

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Fracture Stability

impaction of bone ends

adjacent ligaments soft tissue damage

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Fracture Immobilisation

nothing

plaster

cast brace

internal

plate

intramedullary nail

external fixator

mixture

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Fracture Behaviour

UNCERTAINTY?

TRUST ?

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Fracture Behaviour

STABILITYversus INSTABILITY

STIFFNESS versus STRENGTH

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Why do bones fracture ?

related to crystal structure and collagenorientation

cortical bone is weakest in tension andshear

low energy # follow stress lines

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What types of bone healing ?

primary = union without callus

secondary = union with callus

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Compression Plating

PRIMARYBONE HEALING

rigid plating inhibits # callus

haversian remodelling

contact healing - contact areas

non-contact healing - non contact areas

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Haversian Remodelling

PRIMARYBONE HEALING

revascularise necrotic # ends

reconstitution of intercortical union

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Haversian Remodelling

REQUIRES

exact reduction

stable fixation

existence of a blood supply

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DCP Plates

compression decays with time

50% within 2 months

same decay occurs with intact bone

due to haversian remodelling

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Gap Healing

incongruencies

fill with woven bone

secondary osteons scaffold the gaps

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Primary Bone Healing

oversimplification

often see small amount of callus opposite

a plate

#s healing without callus but have 2ndryhealing

scaphoid and talus = little periosteum or softtissues

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Healing under Plates stress shielding

vascular disturbance

number of cortices

biological fixation

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IM Nails

reamed versus non-reamed

extramedullary callus

slowed collapse and endochondral repair

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External Fixation

primary bone healing can be seen withex-fix

less rigid fixation - controlled motion

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Mechanical Strength of Ex-

Fix

NOTBASEDSOLEYON FIXATOR

composite structure

load sharing device

strength of the bone

HOWMUCH WEIGHTBEARING ?

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How Rigid Should an

Ex-Fix be ?

Controlled micro-movement

Non-union - prevent periosteal new

callus

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Ex-Fix Disassembly ?

Controlled removal

initial stiff frame then more elastic ?

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Ex-Fix Pins

pinholes < 30% of bone diameter

5mm pin 144% stronger than 4mmpin

separate pins greater than 45

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Ex-Fix Frames

11mm tubular rod x2 stiffer than solid

rods of 8mm diameter increasing pin spread increases bending

stiffness

decreasing bone to rod distance increasesbending stiffness

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Rigidity of Ex-Fix

Factor

1 pin diameter2 pin number

3 bone rod distance4 pin group separation

5 Half pin separate > 45

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How to improve pin bone

interface ?

apply half pins rather than wires

wash pins at time of surgery

avoid thermal necrosis - hand drill

pre-loading

dynamization

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Axial Stimulation at the

fracture

PASSIVEDYNAMISATION

due to pin bending

remove side bars and pins

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Axial Stimulation at the

fracture

ACTIVEAXIALDYNAMISATION

weightbearing - without pin bending

relaxation of axial constraint

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Axial Stimulation at the

fracture

CONTROLLEDAXIALDYNAMISATION

controlled force/displacement actuator

cam device

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Circular Ex-Fix

recent innovation

1.8 to 2mm wires

circular rings

anatomic considerations

bending stiffness independent ofloading direction

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Half frame versus

Ilizarov

Ilizarov half as rigid in compression

A-P and torsion comparable

M-L half frame x10 stiffer thanIlizarov

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Ilizarov Frame Stability

larger wire diameter

decrease ring size

use of olive wires

more wires/half pins

cross wires at 90

increase wire tension

centre rings closer to fracture

closer adjacent rings

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Frame Stiffness ?

mono-planar

biplanar circular

THEULTIMATEQUESTION !

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Ex-Fix Summary

ideal construct for external fixation is notknown

can allow for a change incompression/alignment

modulate bone healing between minimal

and maximal callus formation

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