Heterotopic ossification after total hip arthroplasty: When is development completed?

Background Heterotopic ossifications (HO) are a common complication after total hip arthroplasty (THA). Nonsteroidal anti-inflammatory drugs have proven to reduce the occurrence of HO. It is still unclear when the formation of HO is finished. Aim of our study was to answer this question. Methods In a prospective study, the occurrence of periarticular HO was checked during the follow-up (FU) examinations. In total, 75 consecutive patients who underwent THA were included. To ensure a high follow-up rate, only patients with a life expectancy of at least 10 years were included. A medical ossification prophylaxis with mostly etoricoxib (90 mg once daily) was administered. Follow-up examinations were performed at 3 months, 1 year, 3, 5, and 10 years postoperatively. Each time, a clinical and radiological examination was carried out. The HO was graded according to Brooker's method. Results Low-grade HO classified by Brooker grade I and II occurred significantly more frequent than HO grade III. In patients with present HO, a possible increase in Brooker stage could further be observed within 3 years postoperatively. After 3 years, the formation of HO was completed in all patients. Conclusion Three years after THA, the formation of HO is complete. After more than 3 years postoperatively, if HO occurs or increases, other triggering causes such as new trauma, periarticular infection, or implant loosening should be considered.