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

Anterolateral leg bowing is associated with neurofibromatosis type 1 (NF1) frequently leading to fracture and nonunion of the tibia. The objective of the study was to characterize the radiographic findings of tibial dysplasia in NF1. This study is a retrospective review of radiographs of tibial dysplasia obtained within 52 years, between 1950 and 2002, from the Shriners Hospitals for Children, Salt Lake City, and of peripheral quantitative computed tomographic images of 3 individuals with anterolateral bowing of the leg without fracture compared with age- and sex-matched controls. Individuals with NF1 with bowing of the leg have the appearance of thicker cortices with medullary narrowing on plain film radiographs. The peripheral quantitative computed tomographic images of individuals with NF1 with anterolateral bowing show an unusual configuration of the tibia. Anterolateral bowing of the leg in NF1 is associated with the appearance of thicker cortices with medullary narrowing rather than thinning of the long bone cortex on plain film radiographs as currently used as a qualifier in the sixth diagnostic criterion for the clinical diagnosis of NF1. Individuals with NF1 who have anterolateral bowing of the leg have differences in tibial geometry compared with age- and sex-matched controls. The characterization of the radiographic findings of long bone bowing in NF1 helps clarify the NF1 clinical diagnostic criteria.