[Heterotopic ossification after total knee arthroplasty].

OBJECTIVES: The purpose of this study was to determine the incidence, time to development and clinical presentation of heterotopic ossification (HO) after total knee arthroplasty (TKA). METHODS: We retrospectively reviewed consecutive radiographs of 226 knees that were obtained at the end of sixth week, third, sixth, and twelfth months following TKA. The radiographic diagnosis of HO was based on the comparison of pre- and postoperative serial radiographs. Grading of HO was made according to the classification of Figgie et al. The clinical and radiographic course of HO and possible predisposing factors were investigated. No pharmacological prophylaxis was used other than mechanical measures to prevent deep vein thrombosis. RESULTS: Heterotopic ossification was detected only in two knees (0.9%) at the sixth month evaluation of lateral radiographs. It was grade 1 in both knees and localized at the supracondylar area of the distal femur. Both patients had primary osteoarthritis. There were no complaints except for mild nonspecific pain around the knee while standing. In both cases, HO underwent spontaneous improvement and disappeared on the twelfth month radiographs. CONCLUSION: Compared with previous studies, the incidence of HO after TKA was quite low and this could be attributed to the lack of pharmacological thromboprophylaxis. Delayed appearance of HO in two patients suggests that TKA cases be monitored for a longer period for HO development.