Heterotopic bone formation after joint replacement.

Bone formation outside the skeleton, heterotopic ossification (HO), is a common finding on radiographs from patients who have undergone arthroplasty of the hip, knee, shoulder, or elbow. Only a minority (5%-10%) of the patients with HO suffer from any consequence of the condition. However, because of the great number of joint replacements performed, the number of patients with decreased function that can be attributed to HO is significant. The risk for severe HO after total hip arthroplasty is increased in 1) patients who have developed HO after previous surgery, 2) men with hypertrophic osteoarthrosis and, 3) in patients with ankylosing spondylitis or diffuse idiopathic skeletal hyperostosis. The same risk factors are probably valid for other joints as well. Two preventive treatments for HO after hip arthroplasty, nonsteroidal anti-inflammatory drugs and local radiation, are effective and reasonably well documented but are associated with potential side effects. Thus, a treatment protocol to prevent HO must identify the patients at risk for severe HO and recommend them treatment with one of these two modalities. Based on the current literature, we suggest that the patients at risk for severe HO be treated with 1) nonsteroidal anti-inflammatory drugs from the day of surgery for 7-10 days or 2) preoperative (or postoperative) radiation in a single dose.