Excessively Increased Joint-Line Obliquity After Medial Opening-Wedge High Tibial Osteotomy Is Associated With Inferior Radiologic and Clinical Outcomes: What Is Permissible Joint-Line Obliquity.

PURPOSE: This study aimed to evaluate the permissible joint-line obliquity (JLO) based on radiologic and clinical outcomes with midterm follow-up after medial open-wedge high tibial osteotomy (MOWHTO).

METHODS

Patients who had undergone MOWHTO from March 2014 to May 2016 were retrospectively evaluated. They were divided into 4 groups based on JLO as represented by postoperative medial proximal tibial angle (MPTA). Radiologic parameters including MPTA, joint-line orientation angle (JLOA), joint-line convergence angle (JLCA), posterior tibial slope, weightbearing line ratio (WBLR), and coronal translation were analyzed. Clinical outcomes were evaluated with American Knee Society Score (AKSS), Western Ontario and McMaster University Index, and short-form 36 health survey (SF-36). The changes between preoperation and final follow-up in JLOA and MPTA were defined as ΔJLOA and ΔMPTA.

RESULTS

A total of 135 knees were finally included (MPTA ≤90.32° as group I; 90.33° to 92.62° as group II; 92.74° to 95.22° as group III; and ≥95.23° as group IV). The last follow-up MPTA, JLOA, and JLCA values were different between the groups (P < .001, P < .001, and P = .015, respectively). WBLR and JLOA positively correlated with MPTA; however, WBLR showed an abrupt increase at MPTA >96.5°, and the JLOA distribution tended to be greater than the regression line at MPTA >96°. Moreover, ΔJLOA was not as large as ΔMPTA. The percentage of patients attaining a minimal clinically important difference was significantly lower in the AKSS-functional score and SF-36 physical component summary in group IV (P = .008 and 0.021, respectively).

CONCLUSION

The JLOA did not change as much as the MPTA, but an MPTA >95.2° abruptly increased the JLOA and valgus overcorrection after MOWHTO. Poor clinical outcomes were more evident in excessive MPTA (>95.2°) than in mildly undercorrected or properly corrected MPTA (<95.2°).

LEVEL OF EVIDENCE: III, retrospective cohort study.