Preoperative radiotherapy 20-28 hours before total hip arthroplasty versus NSAID prophylaxis for heterotopic ossification: A matched cohort study.

Abstract

Heterotopic ossification (HO) frequently occurs after total hip arthroplasty (THA). Radiotherapy (RT) is an established option for preventing HO when NSAIDs are contraindicated. We assessed the effectiveness of preoperative RT administered 20-28 hours before THA, substantially beyond the guideline-recommended 4-hour preoperative window. We conducted a retrospective 1:3 matched cohort study comparing single-fraction preoperative RT (7 Gy) with postoperative diclofenac 50 mg twice daily for at least 14 days. The primary endpoint was radiographic presence of any HO (Brooker grade > 0). Secondary and exploratory analyses included HO ≥ grade 2, associations with age, sex, and prosthesis fixation type, and potential prophylaxis-by-sex interaction. A total of 344 patients (86 RT, 258 NSAID) were included in the matched cohort. Mean age was comparable (RT: 70.0 ± 9.0 years; NSAID: 69.5 ± 9.0 years). Both groups included 57% female and 43% male patients, and 10% received a cemented prosthesis. HO developed in 18.6% of RT patients versus 22.5% of NSAID patients. Conditional logistic regression showed no statistically significant association between prophylaxis strategy and any HO (OR for RT: 0.79, 95% CI 0.43-1.46; p = 0.449). Exploratory analyses suggested potential sex-specific effect modification: RT was associated with lower odds of HO in men (OR 0.41, 95% CI 0.13-0.92) but not in women (OR 1.54, 95% CI 0.65-3.41), supporting further evaluation of sex as a potential modifier of prophylactic effect. RT delivered 20-28 hours before THA was not associated with increased odds of HO compared with postoperative NSAID prophylaxis. Treatment-effect estimates across the primary, secondary, and ordinal analyses were directionally consistent. However, the retrospective design and width of the confidence intervals preclude conclusions regarding formal non-inferiority or equivalence between strategies. Exploratory analyses suggested that the prophylaxis effect may vary by sex, with a consistent signal of lower HO odds among men receiving RT.