Heterotopic ossification after hip and knee arthroplasty: risk factors, prevention, and treatment.

Symptomatic heterotopic ossification (HO) after total hip arthroplasty (THA) and total knee arthroplasty (TKA) is relatively rare. Patients at high risk for developing HO after THA include men with bilateral hypertrophic osteoarthritis, patients with a history of HO in either hip, and patients with posttraumatic arthritis characterized by hypertrophic osteophytosis. Patients at moderate risk are those with ankylosing spondylitis, diffuse idiopathic skeletal hyperostosis, Paget's disease, or unilateral hypertrophic osteoarthritis. Patients at high risk for developing HO after TKA include those with limited postoperative knee flexion, increased lumbar bone mineral density, hypertrophic arthrosis, excessive periosteal trauma and/or notching of the anterior femur, and those who require forced manipulation after TKA. Preoperative radiation is effective for preventing HO after THA, as are post-operative prophylactic drug regimens and single-dose radiation treatments. Recurrence of HO after surgical excision should be expected unless prophylaxis is administered. Prophylactic measures against HO after THA and TKA should be administered before the fifth postoperative day, optimally within 24 to 48 hours.