DISTRACTION OSTEOGENESIS

Mechanical induction of new bone that occurs between vascular bony surfaces that are gradually pulled apart by gradual distraction.

New bone formed bridges the gap & remodels to normal bone macrostructure.

Tension stress effect on growth & genesis of tissues.

Developed by Ilizarov in 1956Highly modular fixators allow formation of

new bone in almost any plane as D.O follows the vector of applied force.

Age: as long as Pt had # healing potential.INDICATION: bone grafting, LLD, nonunion,

deformity, bone defects 2* to trauma, infection, tumor.

Advantages over bone graftingReduces donor site morbidityAutograft is limitedNo fear of transmission of antigens,

bacteria, viruses, dead foreign bodies.In infected wounds.Risk of # in B.G over extended period of

timeB.G will never incorporate in to living B.

Components of D.O Application of ext.fix – stability, applies

forces Corticotomy Postop period 1. Latency period2. Distraction P.3. Consolidation P.

DEFINITION

CORTICOTOMY: low energy osteotomy, performed using an osteotome to cut only the cortical surface thus preserving the medullary canal, nutrient vessel, endosteum, periosteum

LATENCY PERIOD: Initial healing response is allowed to bridge the cut surfaces before distraction is initiated.

Rate: no of millimeter that the bone surfaces are pulled apart each day.

Rhythm: no of distractions per dayHealing index: no of centimeters of N.B

divided by no of months from the surgery to date of full wt bearing.

Transformation osteogenesis: conversion of non osseous tissues such as fibrocartilage in nonunion in to normal bone. Done through comb compression & distraction forces, augmented by corticotomy.

Bone transportation: regeneration of intercalary B.D through corticotomy & distraction & tranf. Osteogenesis.

Critical factors for B. formationStability of fixation [circular F]Atraumatic corticotomy.RateRhythm of distraction.

HISTOLOGYLATENCY P: similar to # healingDISTRACTION P: mesenchymal cells begin to

organize in to bridge of collagen & immature vascular sinusoids, bridge formed always parallel to direction of distraction.

I Week Distraction: central zone of relatively avascular fibrous tissue bridges the 7 mm of C.gap.

FIZ: fibrous interzone [no osteoid/ O.B]

II WEEK - DistractionClusters of osteoblasts appear on each side of

FIZ adj to vascular sinuses. Collagen bundles fuse with osteoid like M.1* bone spicules –enlarge gradually by

circumferential apposition.Later osteoid began to mineralize the 1*B.S

PMF[primary mineralisation front]PMF – extend from both corticotomy site,

towards the central FIZ.

III Week Mineralization process continues.As the gap increases, bridge is formed by

elongation of bone spicules.Large thin sinusoids surround each micro

column of new bone MCF [micro column formation].

At the end of D., FIZ ossifies & MCF unifies completely bridging the gap.

Microcolumn new bone formation

PhysiologyFibrous interzone assumes the role of

growth plate. [pseudo G.P]Intramembranous ossification in its purest

form. [if stability]Local & regional blood supply is most

important determining factor.

PathophysiologyExcessive rateSporadic rhythmFrame stabilityPoor local & regional stabilityTraumatic corticotomyInadequate consolidation phase.Initial diastasis.

Rate & Rhythm: biosynthetic pathways at cellular levels , protein synthesis & mitosis.

Macromotion: [shear force] disrupt the delicate bone & vascular channels

Peripheral vascular diseaseTraumatic corticotomy- disturb the local blood

flowInitial diastasis- inhibit the formation of 1*

fibrovascular bridge.

Indications for increase in R & RYoung Pt [up to 12-14 yrs]X ray premature consolidation.X ray uncompleted bone cut at the site

of corticotomy. In any event, increase in distraction

speed & rhythm cannot exceed 2 mm/ day.

Indication for reduction Severe pain at the site of distraction, esp

after creating 3-4 cm gap. Clinical signs of peripheral vascular &

neurological deficiency. X ray slow development of

regeneration Reduction in D cann’t be less

than .25- .50 mm/ day .

Ilizarov recommended that the number of actual distractions (rhythm of distraction) should be at least four, achieving a total of 1 mm of total distraction (rate of distraction) in four divided doses.

constant distraction over a 24-hour period produces a significant increase in the regenerate quality

ASSESSMENTCorticotomy: check for completeness in C-

arm. Distracting <2 mm, angulation < 10-15*, rotating < 20-30*.

Adequate reduction of corticotomy gap.Length & alignment of D.G checked weekly

or biweekly by X ray.N.B mineralization appears by 3rd wk of D. –

fuzzy, radiodense columns extending from both cut surfaces

N.B formation should span entire cross sectional area of host bone cut surfaces.

N.B appears bulging, FIZ is narrowing distraction should be accelerated.

N.B shows as hour glass appearance, FIZ widens D. rate reduced.

USG: not regularly used. Cyst formation stop distraction, gap is gradually closed.

QCT: [Quantitative C.T] measuring the mineralization of osteogenic area.

Compared with similar region on normal contralateral limb described as % of normal.

Normally FIZ- 25-35%, PMF- 40-55%, MCF- 60-70%.

Triphasic bone scan: both sides of distraction gap should be hot in all three phases.

If it is cold, stop distraction.

consolidationPlain x rays – monthly basis, condition of

the cortex & medullary canal are noted in the osteogenic area – orthogonal views

Bone density may appear reduced.QCT- demonstrates stability.

ACCORDION TECHMonofocal compression- distraction tech for

nonunion treatment.Alternate compression & distraction

maneuver is used 2-3 times to stimulate bone neogenesis.

Local scar tissues are initially crushed to be transformed in to tissues capable of neogenesis.