This study aimed at determining whether overcorrection after open wedge high tibial osteotomy (OWHTO) would be predicted by the magnitude of preoperative medial and lateral coronal soft tissue laxity around the knee joint.
Overall, 68 knees of 62 patients who underwent OWHTO for primary medial osteoarthritis were retrospectively reviewed. The mechanical hip-knee-ankle (HKA) axis, weight-bearing line (WBL) ratio, medial proximal tibial angle (MPTA), joint line obliquity, coronal subluxation, and joint line convergence angle (JLCA) were measured on full-weight-bearing long-standing HKA radiographs preoperatively and at 1 year postoperatively. The varus valgus stress angle was measured on preoperative radiographs. The correction amount due to soft tissue factors was calculated as the difference between the WBL ratio on postoperative 1-year radiographs and that on virtually corrected preoperative radiographs with the same amount of MPTA at 1 year postoperatively. The patients were grouped according to the presence or absence of a ≥ 10% overcorrection of WBL ratio (overcorrection or expected correction). Multiple logistic regression analysis was performed to identify the preoperative risk factors of overcorrection.
The average WBL ratio was corrected from 19.0 ± 13.5% preoperatively to 61.6 ± 9.1% postoperatively (P < 0.001). The average MPTA changed from 85.1 ± 1.7° preoperatively to 93.6 ± 2.6° postoperatively, resulting in an average tibia correction angle of 8.6 ± 3.1°. The average estimated correction from soft tissue factors was 5.8 ± 7.4% of the WBL ratio. Soft tissue correction of the WBL ratio > 10% was confirmed in 17 patients (28%). The preoperative JLCA and valgus stress angle were significantly greater in the overcorrection group than in the expected correction group: 5.0 ± 1.7° vs. 3.4 ± 1.9° (P = 0.003) and 2.4 ± 1.0° vs. 1.3 ± 1.2° (P = 0.002), respectively. Among the radiologic parameters, the presence of both ≥ 4° JLCA and ≥ 1.5° valgus stress angle was the only significant risk factor for overcorrection from soft tissue factors (P = 0.006; odds ratio, 30.2).
III.
The magnitude of both medial and lateral coronal soft tissue laxity was a predictor of overcorrection from soft tissue factors after OWHTO. Overcorrection was more likely to occur in cases with both ≥ 4° JLCA and ≥ 1.5° valgus stress angle.