Difference in joint line convergence angle between the supine and standing positions is the most important predictive factor of coronal correction error after medial opening wedge high tibial osteotomy

Purpose Coronal correction errors after medial opening wedge high tibial osteotomy (MOWHTO) occasionally occur even with the assistance of navigation. The purpose of the present study was to determine the navigation accuracy in MOWHTO and to identify factors that affect the coronal correction error after navigation-assisted MOWHTO. Methods A total of 114 knees treated with navigation-assisted MOWHTO were reviewed retrospectively. Mechanical axis (MA) on standing radiograph and medial proximal tibial angle (MPTA) were measured preoperatively and at 6 months postoperatively, and the differences (Delta MA and Delta MPTA) were calculated. Joint line convergence angle (JLCA) on supine and standing radiographs was measured preoperatively, and their difference (Delta JLCA) was calculated. To assess the navigation accuracy, Delta MA and Delta MPTA were compared with the coronal correction by navigation (Delta NMA) using intraclass correlation coefficients (ICCs). Univariable and multivariable regression analyses were used to identify factors that affect coronal correction discrepancy (Delta MA - Delta NMA). Results The reliability of navigation was good in terms of bony correction (ICC between Delta NMA and Delta MPTA, 0.844) and fair in terms of MA correction (ICC between Delta NMA and Delta MA, 0.706). The mean coronal correction discrepancy was 2.0 degrees +/- 2.4 degrees. In the multivariable analysis, Delta JLCA was shown to be a predictive factor of coronal correction discrepancy (unstandardized coefficient, 1.026; R-2, 0.470). Conclusion Navigation in MOWHTO provided reliable information about bony correction; however, MA tended to be overcorrected. The difference in JLCA between the supine and standing radiographs was the most important preoperative factor that predicted the coronal correction discrepancy after MOWHTO. In patients with larger Delta JLCA, each degree of Delta JLCA should be subtracted from the planned amount of correction angle when preoperative planning is performed using standing radiographs.