Bone Overgrowth. Disorders of bone growth are fairly common manifestations of neurofibromatosis. They are usually recognized clinically by changes in the overlying soft tissues, with some examples including hemangioma, lymphangioma, elephantiasis, and beaded plexiform neurofibroma (see Plates 4-22 and 4-23). The overgrowth in bones and soft tissue is usually unilateral, involving the limbs, head, or neck. Joseph Carey “John” Merrick, who gained fame in the 19th century as “The Elephant Man,” exemplified the classic case of unilateral bone overgrowth associated with neurofibromatosis. Recently, however, Merrick’s diagnosis of neurofibromatosis has been challenged, with some authors proposing that he had Proteus syndrome.

Because lesions in the limbs occasionally continue to overgrow even after skeletal maturity, epiphysiodesis to equalize limb length should be performed when the diagnosis is confirmed (see Plates 4-35 and 4-36).

Pseudarthrosis of Tibia. An anterolateral bowing deformity in neurofibromatosis may progress to multiple areas of spontaneous fracture followed by pseudarthrosis, known as congenital pseudarthrosis of the tibia (CPT) (see Plate 4-31). The tibial bowing always develops before age 2. It is often progressive and should be treated with a high degree of vigilance. In contrast, posteromedial bowing (which is not associated with neurofibromatosis) is nonprogressive and does not present severe management problems. Anteromedial tibial bowing is classically associated with congenital limb deficiency, such as fibular hemimelia. Management of a fracture associated with CPT is problematic because of its high nonunion rate.

Anterolateral bowing of the tibia in neurofibromatosis has been classified into two types according to the intactness of the medullary canal, involvement of the fibula, and risk of fracture (see Plate 4-31). Type I is an anterolateral bowing with increased cortical density and a sclerotic medullary canal. Type IIA is an anterolateral bowing with failure of tubulation (abnormal medullary canal). Type IIB is an anterolateral bowing associated with a cystic lesion, or prefracture. Type IIC includes anterolateral bowing and frank fracture with pseudarthrosis of both tibia and fibula. Overall, outcome is directly related to the presence of a fracture, location of the fracture within the tibia, and age at the time of fracture.

Type I anterolateral bowing has the best prognosis and may never progress to fracture. Management with bracing is usually unnecessary, unless the bowing starts to increase severely. Corrective osteotomy for the bowing may result in nonunion and pseudarthrosis. Type IIA bowing may lead to fracture, and protective management with an ankle-foot orthosis (prior to walking) or a knee-ankle-foot orthosis (with weight bearing) is essential from the time of diagnosis. Whereas braces are meant to be protective, union with brace management in a fractured tibia rarely results in union. Parents should be educated on the increased likelihood for needed surgical intervention. Type IIB bowing deformity is extremely susceptible to fractures, and, therefore, risk of pseudarthrosis. Attempts to obtain osteosynthesis include various bone-grafting techniques such as massive onlay, inlay, delayed autografts, and turnaround grafts; fixation with an intramedullary rod; vascularized bone (fibular) grafts using microsurgical techniques; and electric stimulation. None of these methods has produced consistent union rates. Additionally, the risk of refracture is high. New techniques are being developed using osteoinductive materials, such as bone morphogenetic protein. This remains an off-label use, with noted variability in union rates in small sample populations. Parents should participate in deciding how many surgical procedures should be attempted before resorting to amputation.