A pathological fracture of the femoral neck associated with osteonecrosis of the femoral head and a stress fracture of the contralateral femoral neck.

A pathological fracture of the right femoral neck associated with osteonecrosis of the right femoral head and a stress fracture of the contralateral femoral neck occurred in a 47-year-old man. Osteonecrosis was noted in almost the entire femoral head, and the pathological fracture occurred at the subcapital area. Six months later, a stress fracture was detected in the contralateral femoral neck. The stress fracture of the left femoral neck might have been caused by the incremental repetitive mechanical loading in the left hip as a result of the pathological fracture in the right hip. Therefore, it might be necessary to conduct a careful examination, using either a magnetic resonance imaging scan or a bone scan, of patients with extensive osteonecrosis of the femoral head because of the risk of osteonecrosis in the contralateral femoral head as well stress fractures in the contralateral femoral neck.