Bilateral non-traumatic aseptic osteonecrosis in the femoral head. An experimental study of incidence.

Thirty-five patients who were seen with non-traumatic aseptic osteonecrosis of the femoral head were included in a study of the contralateral hip to evaluate the incidence of bilateral disease. We used not only conventional radiography and scintigraphy but also measurement of intramedullary pressure and core biopsy. Pain was caused by 14.3 per cent of the contralateral hips, a lesion was demonstrated on plain radiographs in 51.4 per cent, and increased isotopic uptake was seen in 31.4 per cent. Histological study of specimens obtained by osteomedullary biopsy (after special procedure) showed bilateral necrosis in 88.5 per cent of the patients. After a mean follow-up of thirty-four months, only one of nine hips that were painless and had negative radiographic and isotopic findings, but had positive findings on biopsy, became painful and radiographically positive. The intramedullary pressure in the intertrochanteric area was recorded in each hip, and no correlation was found with the radiographic stage or with pain.