High tibial osteotomy (HTO) is a common surgical procedure used to correct axial malalignment and the pathomechanics of the knee. Among 40 knees 35 cases treated by HTO between 1991 and 1993 had pre- and postoperative measurements performed. The purpose of this study was to determine the factors which are related to the results achieved following HTO. Postoperative results are excellent, but there is a tendency for those with a large correction angle (over fifteen degrees) to worsen leading to varus and valgus deformities. The following changes in FTA factors should be measured (1) FTA of the preoperative supine position, (2) correction angle, (3) FTA of postoperative standing position.
