Is preoperative radiation therapy as effective as postoperative radiation therapy for heterotopic ossification prevention in acetabular fractures?

BACKGROUND: Prophylactic approaches to prevent heterotopic ossification after acetabular fracture surgery have included indomethacin and/or single-dose external beam radiation therapy administered after surgery. Although preoperative radiation has been used for heterotopic ossification prophylaxis in the THA population, to our knowledge, no studies have compared preoperative and postoperative radiation therapy in the acetabular fracture population. QUESTIONS/PURPOSES: We determined whether heterotopic ossification frequency and severity were different between patients with acetabular fracture treated with prophylactic radiation therapy preoperatively and postoperatively.
METHODS: Between January 2002 and December 2009, we treated 320 patients with a Kocher-Langenbeck approach for acetabular fractures, of whom 50 (34%) were treated with radiation therapy preoperatively and 96 (66%) postoperatively. Thirty-four (68%) and 71 (74%), respectively, had 6-month radiographs available for review and were included. For hospital logistical reasons, patients who underwent operative treatment on a Friday or Saturday received radiation therapy preoperatively, and all others received it postoperatively. The treatment groups were comparable in terms of most demographic parameters, injury severity, and fracture patterns. Six-month postoperative radiographs were reviewed and graded according to Brooker. Followup ranged from 6 to 93 months and 6 to 97 months for the preoperative and postoperative groups, respectively. Post hoc power analysis showed our study was powered to detect a difference of 22% or more between patients with severe heterotopic ossification. Sample size calculations showed 915 subjects would be needed to detect a 5% relative difference in severe heterotopic ossification status between groups.
RESULTS: We detected no difference in heterotopic ossification frequency between the preoperative (eight of 36, 22%) and postoperative (19 of 71, 27%) groups (p=0.609). There was also no difference in heterotopic ossification severity between groups (p=0.666). Two of 36 (6%) in the preoperative group and three of 71 (4%) in the postoperative group developed clinically significant Grade III heterotopic ossification. No patients developed Grade IV heterotopic ossification.
CONCLUSIONS: We found no difference in heterotopic ossification frequency or severity when comparing preoperative and postoperative radiation therapy. However, given the relatively low frequency of heterotopic ossification in this population, in particular the frequency of severe or symptomatic heterotopic ossification, the possibility of a Type II error must be considered. Larger, prospective studies are required to confirm our no-difference finding, but insofar as the result in this fracture population mirrors that of the THA population, unless our finding is disproven, we believe radiation therapy can be given either before or after surgery, as dictated by the clinical scenario. LEVEL OF EVIDENCE: Level III, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.