Occult posttraumatic avascular necrosis of hip revealed by MRI.

Three hips with avascular necrosis in two patients had associated traumatic lesions noted on magnetic resonance imaging. Location of stress fracture in two femoral necks and acetabular contusion development prior to avascular necrosis favors these processes as being etiologic. These cases are particularly noteworthy in that nondisplaced fractures or other musculoskeletal trauma not visible on plain films has rarely been associated with subsequent development of avascular necrosis.