Distal femoral varus deformity becomes a cause of undercorrection in open wedge high tibial osteotomy.

Abstract

To evaluate whether a high lateral distal femoral angle (LDFA) contributes to undercorrection of lower-limb alignment following medial open wedge high tibial osteotomy (MOWHTO), and to determine the LDFA threshold above which tibial correction alone may be insufficient. This retrospective study analysed 68 patients who underwent MOWHTO at our hospital between 2020 and 2022. Based on their postoperative mechanical axis (MA), patients were categorised into two groups: the acceptable correction group (A-group; MA 57%-67%) and the undercorrection group (U-group; MA ≤ 56%). Radiographic parameters before and after surgery were compared between the two groups. Simple and multiple regression analyses were used to identify factors affecting postoperative MA. A receiver operating characteristic (ROC) curve was utilised to identify the LDFA cut-off value associated with undercorrection. A total of 54 patients met the inclusion criteria (A-group, <i>n</i> = 35; U-group, <i>n</i> = 19). The U-group demonstrated a significantly higher preoperative mechanical LDFA (89.5° vs. 87.6°, <i>p</i> = 0.001) and a lower medial proximal tibial angle (mMPTA) (84° vs. 86°, <i>p</i> = 0.014) than that in the A-group. Both mLDFA (<i>p</i> = 0.006) and mMPTA (<i>p</i> = 0.010) were independent predictors of postoperative MA in multiple regression analysis. The ROC analysis identified an LDFA cut-off of 89.2° for predicting undercorrection (area under the curve = 0.78; sensitivity, 36.8%; specificity, 88.6%). Patients with an LDFA ≥ 89.2° had significantly higher body mass index, joint line convergence angle, varus stress angle, percentage condylar tibial translation and preoperative knee joint line obliquity. A high LDFA (≥89.2°) is associated with an increased risk of undercorrection after MOWHTO, despite accurate tibial correction. These findings suggest that in cases with significant distal femoral varus, isolated tibial osteotomy may be insufficient. Double-level osteotomy, including femoral correction, should be considered in such cases to achieve optimal alignment. Level Ⅳ, retrospective comparative study.