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.