Heterotopic ossification around distal femur after total knee arthroplasty.

Heterotopic ossification after total knee arthroplasty is not well recognized. We found heterotopic ossification around the distal femur in 10 (5%) of 221 knees after primary total knee arthroplasty and evaluated clinical findings as well as risk factors. The duration of follow-up ranged from 1 to 5 years. Most patients with heterotopic ossification showed clinical findings that were suspected of being early infection after surgery such as continuing low-grade fever and erythematous, warm, and swollen knees, whereas blood examinations were normal. Heterotopic ossification developed by a mean period of 5 weeks, and the size increased for a mean period of 9 weeks. The maximum size of the ossification was <5 cm in 9 knees and >5 cm in 1 knee. After that, the size decreased without any treatment in all knees, and the ossification finally disappeared in 2 knees. Osteoarthrosis and the presence of postoperative effusion were the significant risk factors in the development of heterotopic ossification. Although it is difficult to draw valid conclusions from our small study, heterotopic ossification at the distal femur after total knee arthroplasty needed no treatment and was not progressive, nor did it affect the short-term outcome in this study.