Congenital pseudarthrosis of the tibia: biological and biomechanical considerations to achieve union and prevent refracture

Abstract

Congenital pseudarthrosis of the tibia (CPT) is likely to be a primary periosteal disease and secondary bone disease. The primary goal of treatment is to obtain union, correct the diaphyseal deformity, correct any proximal fibular migration and prevent refracture. The pathobiology demonstrates increased osteoclasis by the surrounding fibrous hamartoma and reduced osteogenesis and bone morphogenic protein production by the bone. This leads to a loss of remodelling potential and gradual bowing and atrophy of the bone with eventual fracture of the tibia and or fibula. This recommends the synergistic use of bisphosphonates and bone morphogenic protein. The pathomechanics of CPT implicate the anterolateral bowing, narrow diameter of the atrophic bone ends and proximal fibular migration. These biomechanical factors can be addressed by means of straightening of the deformity, intramedullary support of both bones, stable fixation and reduction of proximal migration of the fibula. A summary of the literature on CPT shows that the mean probability of achieving primary union without refracture, by most treatments is 50% (12% to 80%). Two recent studies have shown a much higher success rate approaching 100%, by creating a cross-union between the tibia and fibula. The cross-union with intramedullary reinforcement of the bone makes refracture unlikely due to the cross-sectional area of union with its two-bar linkage. A new classification to guide such treatment is also proposed.

Level of evidence: V - expert opinion.

Keywords: congenital pseudarthrosis of the tibia; cross-union; neurofibromatosis.

Figures

Fig. 1

Paley Classification of congenital pseudarthrosis of the tibia: type 1, no fractures; type 2, no fracture tibia, fracture fibula with fibula (a) at station (b) proximal migration; type 3, fracture tibia, no fracture fibula ; type 4, fracture tibia and fibula with fibula (a) at station (b) proximal migration (c) bone defect tibia with proximal migration fibula. Reproduced with permission by the Paley Foundation (AP, anteroposterior; LAT, lateral).

Fig. 2

Reproduced with permission by the Paley Foundation: (a) anterior incision shown from front and cross section. Note hamartoma encircling tibia and fibula and the interosseous membrane between them; (b) anterior and deep posterior fasciotomy and muscle reflection to expose tibia, interosseous membrane, and fibula, allow resection of the membrane under direct vision without damage to the neurovascular bundles; (c) circumferential resection of the tibial fibrous hamartoma is carried out over the planned length of the cross-union. The same is done for the fibular hamartoma; (d) the tibial bowing is straightened and the bone ends overlapped and resected; (e) a customized Fassier-Duval telescopic nail is inserted and the male end locked with a wire into the distal epiphysis and the female end screwed into the proximal epiphysis; (f) a small diameter locking plate is fixed medially to the tibia with six screws; (g) the fibular ends can now be cut and the fibula fixed with a wire in its medullary canal; (h) a periosteal graft is harvested from the undersurface of the iliacus muscle. It is then expanded by passing it through the skin graft mesher; (i) decancellousization of the ilium is done by first splitting the two cortical tables of the ilium down to the roof of the acetabulum, triradiate cartilage, sciatic notch, posterior spines and sacro-iliac joint; (j) the periosteal graft is wrapped around the congenital pseudarthrosis site and bone morphogenic protein-2 (BMP2) collagen sponges are inserted overtop the posterior muscles behind the tibia and fibula (left). The cancellous bone is inserted between the tibia and fibula (left centre). The BMP2 sponges are placed overtop the bone graft (right centre). The anterior muscles lie over the BMP2. The interosseous space has a sandwich of cancellous bone between layers of BMP2 and its overlying soft tissues; (k) the cross-union forms between the bones by three months after surgery. The bone is well fixed with the telescopic rod in the tibia, the wire in the fibula and the plate on the tibia (left). Growth may occur despite the hardware leading to telescopic expansion of the male and female rods. The fibular wire descends with growth (left).

Fig. 3

Anteroposterior (AP) (right) and lateral (left) radiographs (a) of right tibia and fibula with anterolateral bowing and neurofibromatosis. This is classified as Paley type 1. AP (left) and lateral (right) radiographs (b) one year after osteotomy of the tibia and fibula with cross-union protocol surgery at age two years. The tibia and fibula are straight fixated with the Fassier-Duval nail and an EVOS plate (Smith & Nephew Orthopedics, Memphis, Tennessee). The upper screws in the plate were removed after six months. There is a long tibio-fibular cross-union present.

Fig. 4

Anteroposterior (AP) (left) and oblique (right) radiographs (a) of right tibia and fibula with anterolateral bowing and neurofibromatosis. The fibula has a pseudarthrosis with a bone defect and has proximal migration. This is classified as Paley type 2b. AP radiograph (b) of tibia and fibula immediately after cross-union surgery three years. Note the large amount of bone graft in the interosseous space. The rod and plate are stabilizing the leg well. The fibular bone defect is spanned by graft and an intramedullary fibular wire. The fibula was moved distally relative to the tibia and is fixed with one of the screws in the plate. AP radiograph (c) taken one year later showing a mature cross-union spanning the interosseous space and the fibular bone defect. The tibia is united end to end. Telescoping is seen in the Fassier-Duval nail indicating growth. The upper screws in the plate were removed after six months.

Fig. 5

Anteroposterior (AP) (left) and lateral (right) radiographs (a) of left tibia and fibula with anterolateral bowing, neurofibromatosis and tibial pseudarthrosis with an intact fibula. This is classified as Paley type 3. AP radiograph (b) six months after cross-union surgery performed at age five years. AP radiograph (c) one and a half years after cross-union surgery. The plate has been removed. The rod was exchanged for a new Fassier-Duval rod.

Fig. 6

Anteroposterior (AP) (left) and lateral (right) radiographs (a) of right tibia and fibula with anterolateral bowing and neurofibromatosis. This is classified as Paley type 4b since there is a pseudarthrosis of both bones and the distal fibula has proximal migration. The bones are very osteoporotic. He has been non-ambulatory for three years. AP tibial radiograph (b) six months after cross-union surgery which was performed at age three years. A well healed bony bridge is already seen. AP radiograph (c) one year after cross-union surgery after the upper screws in the plate were removed.