The natural history of the silent hip in bilateral atraumatic osteonecrosis.

The natural history of presymptomatic ischemic necrosis of the femoral head was studied in the contralateral hip of 15 patients undergoing total hip arthroplasty for avascular necrosis between 1979 and 1984. These 15 hips were retrieved from among 416 patients undergoing total arthroplasty during this time period. Presymptomatic avascular necrosis was defined according to three strict criteria that allowed the hips to be studied from an index entry point (no evidence of avascular necrosis). Follow-up examinations of each of these 15 hips from this entry point revealed that all hips eventually collapsed at a mean of 23 months after index entry point (range, 3-66 months). These data indicate that the "silent hip" is at significant risk of developing avascular necrosis and, if it becomes involved, it progresses to collapse in a high percentage of patients in a relatively short time. There was no correlation between underlying etiology and the time to collapse.