Global varus malalignment increase from double‐leg to single‐leg stance due to intra‐articular changes

Purpose Preoperatively planned correction for tibial osteotomy surgery is usually based on weightbearing long‐leg Xrays, while the surgery is performed in a supine non‐weightbearing position. The purpose of this study was to assess the differences in lower limb alignment in three different weightbearing conditions: supine position, double‐leg (DL) stance and single‐sleg (SL) stance prior to performing a medial opening wedge high tibial osteotomy (MOWHTO) for varus malalignment. The hypothesis of this study was that progressive limb‐loading would lead to an increased preoperative varus deformity. Material and methods This retrospective study included 89 patients (96 knees) with isolated medial knee osteoarthritis (Ahlbäck grade I or II) and significant metaphyseal tibial vara (> 6°). The differences between supine position, DL stance and SL stance were analysed for the hip‐knee‐ankle angle (HKA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), weight‐bearing line ratio (WBL) and joint line convergence angle (JLCA). Results From a supine position to DL stance, the HKA angle slightly increased from 175.5° ± 1.1° to 176.3° ± 1.1° and JLCA changed from 2.0° ± 0.3° to 1.8° ± 0.3° without a statistically significant difference. From DL to SL stances, the HKA angle decreased from 176.3° ± 1.1° to 174.4° ± 1.1° (p < 0.05) and the JLCA increased from 1.8° ± 0.3° to 2.6° ± 0.3° (p < 0.05). A significant correlation was found between ΔHKA and ΔJLCA between the DL and the SL stances (R2 = 0.46; p = 0.01). Conclusion Varus malalignment increases with weight‐bearing loading from double‐leg to single‐leg stances with an associated JLCA increase. Thus, single‐leg stance radiographs may be useful to correct preoperative planning considering patient‐specific changes in JLCA. Level of clinical evidence III, retrospective comparative study.