Main Session
Sep
28
PQA 04 - Breast Cancer, Patient Reported Outcomes/QoL/Survivorship, Functional Radiation Medicine, Hematologic Malignancies, Palliative Care, and International/Global Oncology
2755 - Predictors of Heterotopic Ossification after Acetabular Fixation: Secondary Analysis of a Randomized Trial of Prophylactic Radiation
Presenter(s)
Travis Hoover, MD - University of Maryland Radiation Oncology, Baltimore, MD
T. Hoover1, S. M. Bentzen1, K. Sun1, A. Boissonneault2, N. O'Hara3, G. Slobogean3, M. Sciadini3, J. Nascone3, M. Gage3, J. Y. Lin4, R. V. O'Toole3, and M. V. Mishra1; 1Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, 2Department of Orthopedic Surgery, Emory University, Atlanta, GA, 3Department of Orthopedic Surgery, University of Maryland School of Medicine, Baltimore, MD, 4Department of Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, GA
Purpose/Objective(s):
Radiation therapy (RT) is known to reduce rates of heterotopic ossification (HO) in appropriately selected patients following surgical fixation of an acetabular fracture. We aimed to identify factors that affect risk of HO, efficacy of RT, and wound complication rates.Materials/Methods:
We conducted a post-hoc analysis of a multi-institutional trial that included 104 patients enrolled 2021-2023 at two institutions and randomized 1:1 to post-operative prophylactic RT (7 or 8 Gy in one fraction within 72 hours of surgery) or no RT. Radiographs at least 6 weeks after surgery were evaluated for HO according to the Brooker classification system. Logistic regression modeling was used to identify factors associated with development of any HO, severe HO (Brooker grade 3-4), or wound complications. A heterogeneity of treatment effect (HTE) analysis was performed using interaction testing.Results:
Prophylactic RT significantly reduced the rate of severe HO on both an intention-to-treat (ITT) (3/54 vs 9/50, p=0.047) and as-treated basis (1/40 vs 11/64, p=0.023). On univariate analysis, other factors potentially associated with any HO or severe HO were concomitant head injury, absence of hip dislocation, and associated fracture pattern. On stepwise multivariate analysis, prophylactic RT remained significantly associated with a lower rate of severe HO on both an ITT (OR 0.22, 95% CI 0.05-0.94) and as-treated basis (OR 0.09, 95% CI 0.01-0.80) after adjusting for head injury, fracture pattern, and institution. Among patients who received RT, the dose (7 versus 8 Gy) did not affect the rate of any HO (OR 1.59, 95% CI 0.47-5.41). Similarly, HO rates were not significantly different between those who received RT 0-48 versus 48-72 hours after surgery (OR 0.62, 95% CI 0.21-1.82). Head injury was associated with a higher rate of any HO (OR 3.30, 95% CI 1.13-9.67) and severe HO (OR 4.42, 95% CI 1.07-18.20). Absence of hip dislocation and associated (vs elementary) fracture pattern were associated with a higher rate of any HO (OR 0.37, 95% CI 0.14-0.98) and severe HO (OR 4.42, 95% CI 1.03-18.83), respectively. Sex, age, and race did not appear to affect the rate of HO. RT was not associated with increased wound complications (OR 2.07, 95% CI 0.53-8.11), nor were any other factors tested. On HTE analysis, RT reduced the rate of any HO in males but not females (interaction p=0.037) on an as-treated basis. The effect of RT on severe HO rate (ITT and as-treated) was consistent with regard to sex, race, fracture pattern, use of mechanical ventilation, and presence of head injury or hip dislocation (all with interaction p>0.05).Conclusion:
Single-fraction prophylactic RT (7–8 Gy within 72 hours) reduces severe HO after acetabular fixation without increasing wound complications, with consistent benefit across evaluated subgroups. Patients with concomitant head injury, associated fracture pattern, and absence of hip dislocation appear at elevated risk of HO.