[Peri-articular ossification in total hip prostheses].

The frequency and predisposing factors of ectopic bone formation (EBF) after total hip arthroplasty (THA) are analyzed in 6026 primary THA documented at the M.E. Mueller Foundation in Berne. Series from two clinics [the Lindenhof Clinic in Berne (n = 816) and the Wilhelm Schulthess Clinic in Zürich (n = 612)] are analyzed separately and the results compared with those in the literature. Overall EBF was found in 38.3% of the patients; in 8.6%, it was clinically obvious (grades III and IV according to the classification of Brooker et al.) and is analyzed in this study. EBF was found in 13.4% of the men compared with 4.2% of the women. The frequency of EBF was found to be particularly low in patients with rheumatoid arthritis (4.4%), and EBF was found in 11.4% of patients with post-traumatic osteoarthritis and in 11.1% with idiopathic necrosis of the femoral head. Severe preoperatively limited hip movement did not significantly increase the risk of EBF (11.9%), nor did previous hip surgery, such as intertrochanteric osteotomy (11.3%). Postoperative hematoma that led to puncture or even evacuation was responsible in 14.4%. The therapeutic and prophylactic possibilities are compared with those in the literature, and our personal observations are discussed.