Purpose
To evaluate the center of deformity in varus alignment in a North American population and assess early total knee arthroplasty (TKA) conversion rates and TKA-free survival following medial opening wedge high tibial osteotomy (MOWHTO) based on the bony deformity location.
Methods
A retrospective analysis was performed on 271 digital full-leg standing radiographs of cases with varus alignment who underwent MOWHTO (mean age: 51.6 years; mean follow-up: 3.6 years). Deformity analysis measured the hip-knee-ankle (HKA) angle, mechanical medial proximal tibial angle (mMPTA), and mechanical lateral distal femoral angle (mLDFA) using automated software. An abnormal mMPTA was defined as < 85° and an abnormal mLDFA was defined as > 90°. Cases were classified into four groups based on deformity location: tibial, femoral, combined, or no bony deformity. The differences in TKA conversion rates among groups were analyzed using the chi-square test, while TKA-free survival was determined using Kaplan–Meier survival analysis, with between-group differences assessed using the log-rank test.
Results
The mean HKA angle was 173.0° ± 3.1°. Among the 271 patients, 38% (n = 103), 18% (n = 48), 11% (n = 30), and 33% (n = 90) had tibial, femoral, combined, and no bony deformity, respectively. TKA conversion rates were 3% (n = 3/103), 0% (n = 0/48), 7% (n = 2/30), and 9% (n = 8/90) for the tibial, femoral, combined, and no bony deformity groups, respectively, with no significant difference among the groups (p = 0.080). Kaplan–Meier survival analysis showed no significant difference in TKA-free survival among the four groups (p = 0.185).
Conclusions
In this North American cohort, various varus deformity locations were observed, with isolated tibial deformity being the most prevalent. Additionally, two-thirds of cases exhibited bony deformity, while one-third had no identifiable bony deformity. Regardless of the specific deformity location, the conversion rate to TKA remained low, suggesting that even patients without isolated tibial deformity may still experience a beneficial treatment effect from MOWHTO.