Prophylactic post-operative radiotherapy prevents heterotopic ossification following traumatic acetabular fracture

Purpose/Objective: To determine the effect of post-operative radiation on the incidence of heterotopic ossification following traumatic acetabular fracture. Materials and Methods: A retrospective analysis was performed of the medical records and radiographs of all patients who received prophylactic radiotherapy to prevent heterotopic ossification. These results were compared to a similar group of patients receiving no prophylactic radiotherapy following traumatic acetabular fracture. Between 1987 and 1994, sixty-six patients received prophylactic radiotherapy to prevent heterotopic ossification. Results: Thirty-six patients (55%) received radiotherapy following operative repair of a traumatic acetabular fracture (median follow-up: 210 days). Three dose schedules were utilized: (28(36)) (77.8%) received 700 cGy/1 fx, (2(36)) (5.5%) 800 cGy/1 fx, and (6(36)) (16.7%) 1000 cGy/5 fxs. These patients were retrospectively compared with thirty-four patients who received similar operative management of traumatic acetabular fractures without post-operative radiotherapy (median follow-up: 378 days). Of the patients with heterotopic ossification, 96% developed it within 180 days. Complications and delayed wound healing rates were not significantly different in patients treated with or without post-operative radiotherapy, 6.4% and 6.3% respectively (p=0.49). The incidence of heterotopic ossification at last follow-up in patients treated with and without post-operative radiotherapy was (5(36)) (13.9%) and (19(34)) (55.9%), respectively (p=0.000332). For all patients, type of surgical approach was associated with development of heterotopic ossification: posterior, (7(38)) (18.4%), ilio-inguinal (1(3)) (33.3%), tri-radiate (13(19)) (68.4%), p=.000511. In patients receiving post-operative radiotherapy, variables associated with heterotopic ossification included dose (p=.00962), injury-to-radiation interval (p=.0038), and surgery-to-radiation interval (p=.0238). Fifty percent ((3(6))) of patients receiving 1000 cGy/5 fxs developed heterotopic ossification, while 7% ((2(26))) and 0% ((0(2))) receiving 700 cGy/1 fx and 800 cGy/1 fx developed heterotopic ossification, respectively. In patients with and without heterotopic ossification, the mean injury-to-radiation interval was 23.2 and 7.8 days and the surgery-to-radiation interval was 6.6 and 2.2 days, respectively. Conclusion: Prophylactic post-operative radiotherapy following traumatic acetabular fracture significantly reduces the incidence of heterotopic ossification. Radiation dose, surgery-to-radiation interval, and as yet unrecognized, injury-to-radiation interval are related to the development of heterotopic ossification