Potential anatomic risk factors resulting oversized postoperative medial proximal tibial angle after double level osteotomy

BACKGROUND: Double level osteotomy (DLO) has been introduced to prevent increased postoperative joint line obliquity. However, although DLO is planned, knees with postoperative medial proximal tibial angle (MPTA) > 95° in preoperative surgical planning are present. This retrospective study aimed to evaluate risk factors for an MPTA > 95° in preoperative surgical planning for DLO in patients with varus knee osteoarthritis (OA). METHODS: A total of 168 knees that underwent osteotomies around the knee for varus knee OA were enrolled. The hip-knee-ankle angle (HKA), weight-bearing line (WBL) ratio, mechanical lateral distal femoral angle (mLDFA), joint line convergence angle (JLCA) and mechanical medial proximal tibial angle (mMPTA) were measured on preoperative radiographs. The postoperative WBL ratio was planned to be 62.5%. When the postoperative mMPTA was more than 95° in isolated high tibial osteotomy (HTO), (DLO) was planned so that the postoperative mLDFA was 85°, and residual deformity was corrected by HTO. Knees with postoperative mMPTA ≤ 95° and > 95° were classified into the correctable group and uncorrectable group, respectively. RESULTS: DLO was required in 101 knees (60.1%). Among them, 41 knees (40.6%) were classified into the uncorrectable group. Binomial logistic regression analysis showed that preoperative JLCA and mMPTA were independent predictors in the uncorrectable group. CONCLUSIONS: Even with DLO, postoperative mMPTA was more than 95° in approximately 40% of cases. Preoperative increased JLCA and decreased mMPTA were risk factors for a postoperative mMPTA of > 95° after DLO.