A residual intra-articular varus after medial opening wedge high tibial osteotomy (HTO) for varus osteoarthritis of the knee

PurposeVarus deformity of knee osteoarthritis was formed by both intra-articular and extra-articular pathologies. Such intra-articular deformities could not be fully corrected by a medial open-wedge high tibial osteotomy (HTO), which was performed as an extra-articular procedure. Therefore, the purpose of this study was to investigate whether any residual varus was left inside the joint after HTO in the patients with knee osteoarthritis, and a correlation of the residual varus could be traced.MethodsThis study involved 66 patients (66 knees) undergoing HTO for medial knee osteoarthritis. The percentage of mechanical axis (%MA), mechanical femorotibial angle (mFTA), mechanical lateral distal femoral angle (mLDFA), mechanical medial proximal tibial angle (mMPTA) and joint line convergence angle (JLCA) were measured on radiographs of the full-length legs preoperatively and 6 months postoperatively. The relationship between changes in the JLCA and alignment correction was assessed. The postoperative residual JLCA was categorized as the optimal (postoperative JLCA2 degrees), the acceptable (2 degrees5 degrees) to analyze its correlation with pre- or intra-operative factors.ResultsAverage %MA and mFTA were improved from 5.5 to 60% and from 190.2 degrees to 176.4 degrees, respectively. There was no change in mLDFA, whereas mMPTA changed from 80.3 degrees to 91.8 degrees. JLCA changed from 4.2 degrees to 2.7 degrees. The analyses of multiple linear regression showed that the preoperative JLCA and postoperative changes in mechanical alignment (%MA, mFTA and mMPTA) were two important variables dependently associated with differences in JLCAs postoperatively. However, postoperative JLCAs showed a stronger correlation to preoperative JLCAs than to changes in mechanical alignment postoperatively. A Chi-square analysis showed a significantly higher percentage of patients achieved acceptable postoperative JLCAs in the preoperative JLCA6 degrees group (78.8%) compared to the preoperative JLCA>6 degrees group (6.1%). Therefore, 6 degrees of JLCA was suggested to be a tipping point.ConclusionsThe capability of HTO to correct intra-articular varus deformities, which was represented by JLCAs, is limited. Postoperative residual JLCAs were correlated primarily to preoperative JLCA values and total alignment correction, while the former accounted for most. A preoperative JLCA of 6 degrees was suggested to be a tipping point, and a larger value indicated more than 5 degrees residual JLCA after the HTO.