Tibial Bowing and Pseudarthrosis in Neurofibromatosis Type 1

Anterolateral tibial bowing is a morbid skeletal manifestation observed in 5 of children with neurofibromatosis type 1 NF1, typically identified in infancy. The majority of NF1 individuals with tibial bowing will sustain a fracture that will not heal i.e. pseudarthrosis resulting in multiple surgeries, poor limb function, and amputation. Some NF1 individuals with tibial bowing, however, do not fracture and the bowing improves over time. Clinical predictors to help drive management are lacking, and the pathophysiology of tibial bowing and pseudarthrosis is not well understood. Our objective is to identify clinical predictors of tibial pseudarthrosis and better understand its pathophysiology. We have begun recruitment and assessed many individuals with NF1 with and with tibial bowing. QUS measurements and osteolytic activities have been assessed in the individuals recruited to date, but numbers are small and hence statistically significant conclusions cannot be made. However, 78 individuals with tibial bowing had decreases in speed-of-sound z-scores in the bowed tibia compared to the affected tibia. In addition, we were able to confirm that bone resorption is increased in NF1.