Preoperative standing-supine difference in joint line convergence angle predicts postoperative alignment change after closing-wedge high tibial osteotomy.

PURPOSE: The aim of this study was to identify preoperative determinants of postoperative change in joint line convergence angle (JLCA) after closing-wedge high tibial osteotomy (CWHTO), comparing standing- and supine-based radiographic references for preoperative planning. METHODS: Consecutive patients with medial compartmental knee disorders who underwent CWHTO between February 2009 and September 2017 were retrospectively reviewed. Patients with anterior cruciate ligament reconstruction, unavailable radiographs or non-measurable radiographs were excluded. JLCA was measured on standing, supine and valgus/varus stress radiographs. Postoperative change in JLCA (cJLCA) was calculated from preoperative supine to postoperative standing JLCA (cJLCA [pre-supine to post-stand]) and from preoperative standing to postoperative standing JLCA (cJLCA [pre-stand to post-stand]). The preoperative standing-supine difference in JLCA (dJLCA) was also calculated. Associations between cJLCA and demographic and radiographic variables were evaluated using univariate and multivariable analyses. RESULTS: After excluding patients with anterior cruciate ligament reconstruction (n = 1), unavailable radiographs (n = 7) or non-measurable radiographs (n = 4), 40 patients were included. The cohort included 29 women and 11 men, with a mean age of 60.3 years (range, 39-77 years); postoperative radiographs were obtained at a mean of 9.9 months (range, 2-14 months). Univariate analysis showed that dJLCA was positively correlated with cJLCA (pre-supine to post-stand) (ρ = 0.52, p = 0.001) and negatively correlated with cJLCA (pre-stand to post-stand) (ρ = -0.43, p = 0.007). In multivariable analysis, dJLCA remained independently associated with both outcomes (B = 0.51, p = 0.006; B = -0.49, p = 0.008, respectively). CONCLUSIONS: The preoperative standing-supine difference in JLCA was the primary determinant of postoperative change in JLCA after CWHTO. A greater standing-supine difference was associated with greater undercorrection when supine radiographs were used as the planning reference, but with greater overcorrection when standing radiographs were used as the planning reference. LEVEL OF EVIDENCE: Level IV.