Sciatic nerve compression by preexisting heterotopic ossification during general anesthesia in the dorsal lithotomy position.

This report documents the 4th patient reported with sciatic nerve compression by heterotopic ossification and the 1st case occurring during general anesthesia. A 25-year-old woman developed right sciatic nerve dysfunction after a 30-minute dilatation and curettage in the dorsal lithotomy position. Postoperative x-rays revealed a large area of heterotopic ossification above the right greater trochanter. The patient had sustained a traumatic midshaft fracture of the right femur seven years previously, which required intramedullary nail fixation. It is postulated that during the D and C in the dorsal lithotomy position, the heterotopic ossification was displaced posteromedically, compressing the sciatic nerve that had already been placed at maximal stretch. The patient recovered partially. Electrodiagnostic studies were of considerable value in localization of the lesion and confirmation of the mechanism of injury. It is concluded that preexisting heterotopic ossification of the hip may compress the sciatic nerve during surgery in the dorsal lithotomy position.