A validated method accounting for joint line convergence angle reduces planning errors in medial opening wedge high tibial osteotomy

Purpose: Medial opening-wedge high tibial osteotomy (MOWHTO) correction error can result from either planning or execution, or both. This study aimed to (1) identify factors contributing to planning error, and (2) propose and evaluate a new planning method for reducing planning error. Methods: A retrospective analysis was performed on 58 patients (mean age: 46.7 ± 7.2 years) with varus alignment who underwent MOWHTO using patient-specific implants. Radiographic measurements, including hip–knee–ankle angle (HKA), medial proximal tibial angle (MPTA), joint line convergence angle (JLCA) and knee joint line obliquity (KJLO), were made preoperatively and 6 months post-operatively. Overall error in HKA and surgical error in MPTA were used to calculate planning error (planning error = overall error − surgical error). A multivariable logistic regression analysis identified risk factors for suboptimal planning error (absolute error >1°), and this information was used to create a method to minimize it. Results: Suboptimal planning error was associated with increased standing JLCA (3.9 ± 1.0° vs. 2.0 ± 1.4°; p < 0.001) and valgus KJLO (−0.6 ± 0.9° vs. 1.1 ± 2.5°; p = 0.005); however, multivariable logistic regression analysis identified increased standing JLCA as the only significant risk factor for suboptimal planning error (odds ratio: 3.27; p < 0.001). A preoperative JLCA cut-off of 2.8° yielded 94% sensitivity and 78% specificity for suboptimal planning error. Retrospective ΔJLCA adjustment, performed by subtracting ΔJLCA from post-operative HKA and recalculating planning error, reduced the mean planning error from 0.6 ± 1.0° to 0.2 ± 0.7° (p = 0.010). Conclusion: Preoperative standing JLCA ≥ 2.8° is a significant risk factor for suboptimal planning in MOWHTO, with an increased risk of over-correction in these patients. The ΔJLCA method, which adjusts patient-specific planning by detecting joint laxity preoperatively using standing and supine images, may minimize planning error and improve post-operative alignment. Level of Evidence: Level IV, retrospective case series.