Ectopic ossification after total hip arthroplasty. Predisposing factors, frequency, and effect on results.

In a statistical analysis of 398 consecutive patients with 507 total hip arthroplasties which was designed to identify factors predisposing to ectopic ossification and to determine the frequency of ossification and its effect on the results, it was found that male patients with considerable bilateral osteophytic osteoarthritis were statistically most likely to have ectopic ossification, especially if ossification had existed before arthroplasty consequent to previous surgery. Ectopic ossification which was first noted six weeks after total hip arthroplasty in 96 per cent of the cases did not change in amount thereafter, though the bone did mature. Both the range of motion of the hip and the function of the patient were affected by the ectopic bone during the first postoperative year, but after that only the range of hip motion was influenced.