An Increase in Medial Joint Space Width after Medial Open-Wedge High Tibial Osteotomy Is Associated with an Increase in Postoperative Weight-Bearing Line Ratio rather than with cartilage regeneration: Comparative Analysis of Patients Underwent Second-look Arthroscopic Assessment

Abstract Purpose To investigate relevant factors influencing increases in medial joint space width (JSW) after medial open-wedge high tibial osteotomy (MOWHTO). Methods Between January 2010 and December 2018, the electronic medical records of consecutive patients who underwent MOWHTO and subsequent second-look arthroscopic assessment at least 12 months after MOWHTO were retrospectively evaluated. The patients were classified into two groups according to changes in the medial JSW of the knee at the time of second-look operation, compared to that at baseline before the initial surgery. Various radiographic parameters, arthroscopic findings, and clinical scores were compared between the groups, and regression analysis was performed to identify factors related with increases in medial JSW. Results A total of 114 patients were analyzed. In bivariate analysis, patients who experienced an increase in medial JSW showed significantly higher postoperative weight-bearing line ratios (WBLR) (P=.008) and a greater proportion of severe preoperative cartilage lesions in the medial compartment of the knee, compared to patients with maintained or reduced medial JSW (P=.035). In terms of clinical scores, patients with an increased medial JSW showed relatively favorable clinical outcomes at the time of the second-look operation. Regression analysis indicated only postoperative WBLR as a relevant factor associated with an increase in medial JSW after MOWHTO (odds ratio=1.057, P=.01). Additional analysis with patients reclassified according to postoperative WBLR demonstrated that as postoperative WBLR increased, medial JSW increased without a significant change in lateral JSW. Conclusions An increase in the medial JSW of the knee joint after MOWHTO appears to be associated with an increase in postoperative WBLR, not with cartilage regeneration. Obtaining adequate correction so that postoperative WBLR is within 60-70% would be desirable in terms of postoperative changes in medial JSW, as well as clinical outcomes.