Congenital pseudarthrosis of tibia

definition

· specific type of non union or potential non union

· occurs through a hamartomatous area in the tibia

· present at birth

· associated with anterolateral bowing

· term used to include

· all congenital fractures of the tibia

· pseudarthrosis of tibia arising after pathological fracture in tibia with congenital bowing

· bowing usually occurs at junction of middle and distal thirds

epidemiology

· rare disease (1:200 000)

· 40-80% have neurofibromatosis

· 1-3% of patients with neurofibromatosis have CPT

aetiology

· cause unknown

· theories include

· intrauterine trauma

· localised vascular abnormality of tibia

· constriction due to proliferating fibrous tissue

· localised lesions (eg. fibrous dysplasia)

pathology

· hamartomatous cuff present at site of lesion site

· even with associated neurofibromatosis, no clear histological evidence that the fibrous tissue is a neurofibroma

classification

Crawford

· simplest classification

· anterolateral bow plus

Type 1 - nondysplastic

· nondysplastic

· increased cortical density

· normal medullary canal

Type II - dysplastic

II-A

· increased medullary canal width

· failure of tubulation

II-B

· cystic postfracture lesion

II-C

· fracture, cysts and frank pseudarthrosis

Boyd

· most complete classification

Type 1

· congenital anterior bowing

· defect present in tibia on x-ray

· other congenital deformities may be present

· rare

Type II

· congenital anterior bowing

· hourglass constriction of tibia

· spontaneous fracture or fracture after minor trauma usually occurs before age 2

· tibia is tapered, rounded and sclerotic

· medullary cavity not continuous on x-ray

· most common and has worst prognosis

· prognosis worse when there is associated neurofibromatosis

· 50% of cases

Type III

· fracture develops at site of bone cyst

· usually near junction of middle and distal thirds

· anterior bowing may precede or follow development of fracture

Type IV

· sclerotic segment of bone initially present at junction of middle and distal thirds

· segment may produce complete or partial obliteration of medullary canal

· no narrowing of tibia

· fracture develops similar to stress fracture

· fracture does not heal and develops into pseudarthrosis

Type V

· congenital dysplastic tibia

· bowing usually present but not severe

· pseudarthrosis may or may not develop

Type VI

· intraosseous neurofibroma or schwannoma

· pseudarthrosis may or may not develop

· very rare

treatment

Principles

· difficult conditions to treat

· will not heal by casting alone

· before fracture has occured, treatment is preventative (bracing)

· after fracture, treatment is surgical

· treatment depends on

· age of patient

· type of pseudarthrosis

· surgery indicated as early as feasible

· the longer grafting delayed, the shorter and more poorly developed leg will be

· likelihood of obtaining union increases with increasing age

Surgical techniques

Bone grafting

· may be performed prophylactically in concavity of bowed tibia

· grafting alone is method of choice for type III lesion

· less successful for type II lesion (30%)

Osteosynthesis

· should be first approach for type II lesion

· is most reliable technique at present

· technique described by Umber, Moss and Coleman

Operative technique

· approach tibia through anterior incision

· excise hamartomatous (fibrous) tissue

· excise enough sclerotic bone

· balance between

· sufficient resection to leave good quality bone at each end

· preservation of enough bone to minimise leg length discrepancy

· apply autogenous iliac bone graft

· move muscle over graft site

· fix tibia with intramedullary rod extending from calcaneus across ankle and into proximal tibial metaphysis

· use Steinmann pin, Rush nail or intramedullary nail depending on size of patient and medullary canal

· with progressive growth, rod migrates proximally and eventually ankle joint is free

· concurrently graft and rod any coexisting fibular pseudarthrosis

· some suggest to use fibular rod regardless to improve distal fixation

· prolonged postoperative immobilisation

· initially in spica cast for 6 months

· once union achieved, protective brace until skeletal maturity

· encourage early weight bearing

· rods left in place until skeletal maturity to pevent refracture

· 60% union rate

Vascularised free fibular graft

· pseudarthrotic segment resected and replaced by living contralateral fibula

· good results reported

· has advantage that can achieve

· primary bone lengthening

· correction of deformity

· union occurs in relatively short period of time

· technically demanding procedure

· requires microsurgical experience

· involves operation on normal leg

· major problem is development of valgus deformity of normal ankle

· due to overgrowth of distal tibial epiphysis

· distal fibula acts as tether

· treated with tibiofibular synostosis

· can be overcome by using ipsilateral fibula

· only possible if fibula not involved

Ilizarov technique

· pseudarthrosis resected

· corticotomy of proximal metaphysis performed

· 3-level ring fixator applied

· middle tibial segment moved distally to provide metaphyseal lengthening and pseudarthrosis compression

· allows

· bone lengthening

· correction of deformity

· excellent union rates

Amputation

· for severe lesions with poor prognosis

· decision should be made before too much invested in saving limb

· amputation may be performed through lesion or through ankle (Syme)

Electrical stimulation

· independent use of doubtful benefit

· may be combined with grafting and rodding

prognosis

· varies with type

· worse with

· congenital or early onset

· shortening

· tapering

· sclerosis

· failure of operative repair with graft resorption

· leads to amputation in 50%

· 25% of patients develop CNS glioma