Determinants of Heterotopic Ossification after Total Hip Replacement Surgery

The ability of various pre- or peri-operative variables to determine the risk of developing moderate to severe heterotopic ossification (HO) six to twelve months after surgery was investigated among 407 patients undergoing elective total hip replacement (THR) surgery and allocated to placebo in a randomised controlled trial evaluating NSAIDS-based prophylaxis for HO. Overall, 11 (30%) of the 37 patients undergoing revision surgery developed moderate to severe HO compared with 58 (16%) of the 370 patients undergoing primary THR; odds ratio (OR) 2.3, 95% confidence interval (CI) 1.1 to 4.9. Among patients undergoing primary THR, mutually adjusted analysis of collected independent risk factors demonstrated that receiving a transfusion of red cells or having general as well as epidural or spinal anaesthesia present as indicators of increased risk for developing moderate to severe HO. Patients who have undergone revision surgery have a significantly increased risk of clinically relevant ectopic bone, while among patients who have undergone primary THR surgery, those with indicators of excessive surgical bleeding are also at increased risk of clinically relevant HO.