What Is An Acceptable Limit of Joint-Line Obliquity After Medial Open Wedge High Tibial Osteotomy? Analysis Based on Midterm Results

Background: Although joint-line obliquity (JLO) after open-wedge high tibial osteotomy (OWHTO) is commonly encountered, especially in cases of overcorrection, its effect has not been fully elucidated or has been assessed only in the short term. The acceptable range of JLO, often recognized as <= 4 degrees, has not been determined as per the midterm outcomes of OWHTO. Hypothesis: Joint-line obliquity exceeding the acceptable limit after OWHTO would accelerate cartilage degeneration and adversely affect midterm clinical outcomes. Study Design: Cohort study; Level of evidence, 3. Methods: A total of 109 patients who underwent OWHTO between 2010 and 2015 with a mean follow-up period of 55.0 months (range, 24-102 months) were reviewed. JLO was defined as the angle between the lines parallel to the floor and to the tibial plateau on a long-standing hip-to-ankle radiograph. For radiologic evaluation according to JLO, the medial joint space width (JSW) was measured on a standing 45 degrees flexion posteroanterior view and standardized with the width of the tibial plateau as reference, after which changes in JSW (Delta JSW) between the 6- and 12-month postoperative period and the latest follow-up were calculated. Delta JSW was analyzed according to 2 different cutoff values of JLO: JLO of 4 degrees, which is currently recognized as the acceptable limit, and that derived from the receiver operating characteristic (ROC) curve for the third quartile of Delta JSW. Multivariate regression analysis including JLO as well as other demographic and radiologic factors was performed. Clinical outcomes were evaluated in the same way using Knee Society (KS) objective and functional scores. Results: With a JLO cutoff of 4 degrees in the multivariate regression analysis, JLO was not significantly associated with Delta JSW (P= .545). However, in the KS objective and functional score analyses, JLO >= 4 degrees was found to be a significant factor (P= .045 and .005, respectively). The ROC curve showed a cutoff JLO of 6 degrees, which was significantly associated with Delta JSW (P= .001). JLO >= 6 degrees remained significant in the analyses for KS objective and functional score (P= .012 and .001, respectively). Conclusion: The adverse effect of JLO on radiologic outcomes was shown when JLO was >= 6 degrees. In clinical aspects, worse outcomes were found in cases of JLO >= 4 degrees.