Ectopic bone formation following Charnley hip arthroplasty.

In a consecutive series of 309 patients the degree of ectopic bone formation was assessed 3 months, 2 years, and 5 years after total hip arthroplasty. At the three follow-up examinations ectopic bone formation was found in 49 per cent, 61 per cent, and 71 per cent. In men ectopic bone formation was more common and more pronounced than in women. It was demonstrated that walking ability and range of hip movement may be reduced in the presence of ectopic bone formation. A past history of hip surgery, preoperative exostoses, and postoperative elevation of the erythrocyte sedimentation rate did not appear to influence the formation of ectopic bone. There was no correlation between the degree of ectopic bone formation in the two hips of patients who had undergone bilateral operation. In the present study it was not possible to demonstrate preoperatively which groups of patients are most liable to develop ectopic bone postoperatively.