PREVENTION OF HETEROTOPIC OSSIFICATION ABOUT THE HIP - FINAL RESULTS OF 2 RANDOMIZED TRIALS IN 410 PATIENTS USING EITHER PREOPERATIVE OR POSTOPERATIVE RADIATION-THERAPY

Purpose: Experimental and clinical data support effectiveness of perio perative radiotherapy to prevent heterotopic ossification after hip su rgery or trauma. Since 1987, two prospectively randomized trials were performed in patients with high-risk factors to develop heterotopic os sification: the first (HOP 1) to assess the prophylactic efficacy of p ostoperative low vs. medium dose radiotherapy, and the second (HOP 2) to assess the prophylactic efficacy of pre vs. postoperative radiother apy. Methods and Material: 410 patients with high risk to develop hete rotopic ossifications about the hip following hip surgery were recruit ed. Between June 1987 and June 1992, 249 patients were randomized in H OP 1 to postoperative ''low dose'' (5 x 2 Gy; total: 10 Gy) or ''mediu m dose'' (5 x 3.5 Gy; total: 17.5 Gy) radiotherapy. Between July 1992 and December 1995, 161 patients were randomized in HOP 2 to either 1 x 7 Gy preoperatively (less than or equal to 4 h before surgery) or 5 x 3.5 Gy (total: 17.5 Gy) postoperatively(less than or equal to 96 h af ter surgery). With exception of age and type of implant (cemented vs. uncemented prosthesis) all confounding patient variables (gender, prio r surgery) and predisposing risk factors were similarly distributed be tween both trials and treatment arms. Portals encompassed the periacet abular and intertrochanteric soft tissues. Radiographs were obtained p rior and immediately after surgery and at least 6 months after surgery to assess the extent of ectopic bone formation about the hip. Modifie d Brooker grading was used to score the extent of heterotopic ossifica tion. Harris scoring was applied to evaluate the functional hip status . If the scores decreased from immediate post or preoperative status, respectively, to the last follow-up, radiological or functional failur es were assumed. Results: Effective prophylaxis was achieved in 227 (9 1%) hips of HOP 1 and in 142 (88%) of HOP 2. In HOP 1, 15 (11%) radiol ogical failures were observed in the law-dose group compared to 7 (6%) in the medium dose group (p > 0.05). In HOP 2, 4 (5%) radiological fa ilures were observed in the postoperative and 11 (19%) in the preopera tive group (p < 0.05). Subgroup analysis of the preoperative group rev ealed that the highest failure rate occurred in patients with prophyla ctic radiotherapy prior to removal of ipsilateral Brooker Grade III an d IV ossification (39%) (p < 0.001), while all other patients in the p reoperative group had a failure rate that was comparable to postoperat ive treatment groups. In multivariate logistic regression analysis the number of high-risk factors for development of heterotopic ossificati on (p = 0.03) and the time to RT initiation (p = 0.05) were independen t prognostic factors in the HOP I study. For the HOP 2 study, the mult ivariate logistic regression analysis revealed the number of high-risk factors for development of heterotopic ossification (p = 0.003), the preoperative HO grade (p = 0.001) and the RT dose concept (p = 0.05) a s independent prognostic factors. Other factors including type of impl ant( cemented vs. uncemented) did not affect the prophylactic efficacy of radiotherapy. There were no increased intra-and postoperative comp lications seen in the preoperative group, and no long-term complicatio ns were observed in both HOP studies. For functional failures (decreas e of Harris score) no statistically prognostic factors were found. The re were less functional failures in HOP 1 (18 = 7%) than in HOP 2 (23 = 14%, but this difference was not statistically significant. Only pat ients with high Brooker Grade III and TV at last FU achieved a lower H arris score than those with low Brooker Grade 0, I and II (p < 0.05).C onclusion: With the exception of a small subgroup of patients with ips ilateral high Brooker Grade III and IV, pre-and postoperative radiothe rapy are equally effective to prevent heterotopic ossification about t he hip after hip surgery and total hip arthroplasty. Fractionated medi um dose radiotherapy resulted in the lowest failure rate. (C) 1997 Els evier Science Inc.