Adequately increased postoperative medial proximal tibial angle can prevent medial joint space narrowing after open-wedge high tibial osteotomy: a 3-year cohort study

Purpose This study aimed to investigate the longitudinal relationship between postoperative medial proximal tibial angle (pMPTA) and joint space narrowing or osteophyte formation during a 3-year follow-up period after medial open-wedge high tibial osteotomy (MOWHTO). Methods This retrospective cohort study included 133 knees of 101 patients (58 female patients; 77 female knees) who underwent MOWHTO [mean age: 57.5 ± 7.9 years; body mass index: 26.3 ± 4.0 kg/m 2 ; 32 patients (19 female patients) underwent bilateral surgeries]. On the basis of plain radiograph until 1 month postoperatively (Post Op), pMPTA and change in MPTA (ΔMPTA) (i.e., [pMPTA] − [preoperative MPTA]) were measured. Additionally, the medial and lateral femorotibial joint space widths (MJSW/LJSW) and osteophyte area (MOPA/LOPA) were measured at Post Op, and the JSW and OPA were remeasured at 3-year follow-up (3Y). Amount of changes in JSW and OPA were measured using the following formula: Δ = [JSW 3Y or OPA 3Y ] − [JSW Post Op or OPA Post Op ]. If ΔMJSW was ≤ −0.3 mm, we defined medial knee osteoarthritis as progressed (p-mOA). Results Forty-seven (35.3%) patients were diagnosed with p-mOA. Both pMPTA and ΔMPTA positively correlated with ΔMJSW. Receiver operating characteristic curves of pMPTA detected p-mOA, and the cut-off of pMPTA was 90°. Generalized estimation equations revealed that those with < 90° of correction for pMPTA demonstrated higher odds ratio of p-mOA (odds ratio: 3.300; 95% confidence interval: 1.327–8.198, p -value: 0.010), as compared with those with ≥ 90° correction. This finding was more robust in patients with preoperative Kellgren–Lawrence grade 0 or 1 (odds ratio: 5.408; 95% confidence interval: 1.400–20.905, p -value: 0.014), and ΔLJSW did not correlate with both pMPTA and ΔMPTA. Both the MOPA and LOPA increased during the 3-year follow-up period. However, there was no correlation between ΔOPA and pMPTA or ΔMPTA. Conclusions Only in those with nonradiographic OA, correcting pMPTA with < 90° demonstrated a higher odds ratio of medial femorotibial joint space narrowing after MOWHTO when compared with those having ≥ 90° correction in the current short-term follow-up. Level of evidence : III.