The impact of class III (morbid) obesity on heterotopic ossification outcomes

Purpose: Obesity is associated with a chronic low inflammatory process that may act as common soil for the pathogenesis of obesity-related comorbidities including heterotopic ossification (HO). The purpose of this study is to compare the incidence of HO between patients with body mass index (BMI) <40 versus ≥40 after operative treatment of displaced acetabular fractures followed by radiation therapy (RT) ± indomethacin. Methods and Materials: This is a single institution retrospective chart review of 419 patients. All patients with well-documented BMI underwent operative treatment followed by RT ± indomethacin. All patients received 700 cGy to the soft tissues around the proximal femur and acetabulum without bone shielding. All RT were given postoperatively within 72 hours. The patients were divided into 2groups: Group (A) BMI < 40 and Group (B) BMI ≥40. HO was assessed with X-ray. BMI was used as a surrogate measure to test the risk of HO despite prophylaxis. Results: The incidence of HO among all patients is 21% (89 of 419), while among those in group A (BMI <40), 68 of 374 patients developed HO (18%); in the morbidly obese group (BMI ≥40) 21of 45 patients developed HO (47%). The difference between the rates of HO in the 2 groups was 29%; the χ ² test showed a significant difference between the 2 BMI groups (P < .001 at α = 0.05). Conclusions: There is a higher incidence of HO among the morbidly obese patients despite RT ± indomethacin. RT doses for HO prophylaxis in morbidly obese patients need to be reassessed; also, understanding the signaling pathways in target tissues in obese patients at which adipokines control metabolism may reveal novel therapies. Higher radiation doses ± indomethacin may need to be considered and optimally evaluated in the context of a prospective, randomized clinical trial.