Analysis of radiographic characteristics of anterolateral bowing of the leg before fracture in neurofibromatosis type 1.

Background—Anterolateral lower leg bowing is associated with neurofibromatosis type 1 (NF1) frequently leading to fracture and non-union of the tibia. The objective of the study is to characterize the radiographic findings of tibial dysplasia in NF1. Methods—Retrospective review of radiographs of tibial dysplasia from the Shriners Hospitals for Children, Salt Lake City over 52 years between 1950 and 2002, and peripheral quantitative computed tomography (pQCT) imaging of three individuals with anterolateral bowing of the leg without fracture compared to age- and gender-matched controls. Results—NF1 individuals with bowing of the lower leg have the appearance of thicker cortices with medullary narrowing on plain film radiographs. The pQCT images of NF1 individuals with anterolateral bowing show an unusual configuration of the tibia. Conclusions—Anterolateral bowing of the lower leg in NF1 is associated with the appearance of thicker cortices with medullary narrowing on plain film radiographs rather than “thinning of long bone cortex” as currently utilized as a qualifier in the 6 th diagnostic criterion for the clinical diagnosis of NF1. Individuals with NF1 who have anterolateral bowing of the lower leg have differences in tibial geometry compared to age- and gender-matched controls. Clinical Relevance—The characterization of the radiographic findings of long bone bowing in NF1 helps clarify the NF1 clinical diagnostic criteria.