Interobserver reliability and intraobserver reproducibility of the modified Ficat classification system of osteonecrosis of the femoral head.

Anteroposterior and lateral plain radiographs of 116 osteonecrotic femoral heads were reviewed to assess the interobserver reliability and intraobserver reproducibility of the modified Ficat classification system. The radiographs were reviewed initially and then again six months later by three adult reconstructive surgeons, two general orthopaedic surgeons, two orthopaedic residents, and one musculoskeletal radiologist. All eight observers agreed on the classification of twenty hips (17 per cent) at both the first and the second review of the radiographs. Paired comparisons revealed a mean interobserver kappa reliability coefficient of 0.46 (range, 0.30 to 0.67) for the first review and 0.45 (range, 0.30 to 0.66) for the second. For all observers, the mean rate of perfect agreement between the first and the second review was 68 per cent (range, 56 to 80 per cent). The mean kappa value for intraobserver reproducibility was 0.59 (range, 0.44 [one of the residents] to 0.73 [one of the general orthopaedic surgeons]). No observer or pair of observers had excellent reproducibility or reliability (kappa > 0.75). The poor interobserver reliability and fair intraobserver reproducibility diminishes any meaningful comparison of studies in which the modified Ficat classification system has been used and illuminates the need for a more reliable and reproducible classification system.