Protrusio acetabuli in neurofibromatosis: nondysplastic and dysplastic forms.

Protrusio acetabuli (PA) in neurofibromatosis is not well documented in the literature. Two forms of PA, a nondysplastic and dysplastic type, are noted. Twenty-one percent of hips (13 patients) in neurofibromatosis were found to have some form of acetabular protrusion abnormality. In the control group (83 patients) without stigmata of neurofibromatosis, only 9% of hips were associated with PA. The progressive dysplastic form of PA is usually associated with contiguous soft-tissue neurofibromas and lumbar dural ectasia. The nondysplastic, nonprogressive form has less of an association with regional soft-tissue abnormalities and almost no association with dural dysplasia.