Summary

Correction to at least neutral alignment during high tibial osteotomy for varus knee osteoarthritis is sufficient in reducing the knee adduction moment.

Abstract

Introduction

High tibial osteotomy (HTO) for varus knee osteoarthritis traditionally aims to overcorrect the mechanical tibiofemoral angle (mTFA) to become valgus. However, valgus overcorrection in HTO increases problems such as knee joint line abnormality, hinge fracture, and patellar height change. Thus, there is a trend to avoid overcorrection, but there is a lack of biomechanical basis for abandoning the traditional overcorrection. From a dynamic perspective, medial-to-lateral knee joint load distribution during gait can be reflected as knee adduction moment (KAM), and dynamically, the main purpose of HTO is to reduce the KAM increased during gait due to varus alignment. This study aims to reveal the association between the KAM obtained from 3-dimensional (3D) gait analysis and various static alignment parameters, including mTFA, measured from the standing whole limb anteroposterior radiograph, and through this, to suggest a dynamically optimal target for HTO.

Material And Methods

In a general population cohort, 937 lower extremities were enrolled. Correlations were assessed using Pearson's coefficient between the positive KAM-time integral (only area under the curve and above the time axis of the KAM-time graph of the gait cycle) and the maximum KAM and age, sex, anthropometric parameters, Kellgren-Lawrence (K-L) grade, mTFA, medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), knee joint line orientation, ankle joint line orientation (AJLO), joint line convergence angle, and coronal tibiofemoral translation. Multiple regression analyses with backward eliminations for the KAM variables were conducted with variables significantly correlated with the KAM. ANOVA and post-hoc analyses were performed among lower extremities grouped according to the mechanical alignment by the interval of 1°.

Results

Among the variables, mTFA had the strongest correlation with both the positive KAM-time integral and the maximum KAM (r=0.376 and 0.383, respectively), followed by AJLO (r=-0.258 and -0.269). Both KAM values had positive correlation with age (r=0.145 and 0.103), male sex (r=0.125 and 0.087), medial K-L grade (r=0.140 and 0.106), and LDFA (r=0.184 and 0.199) but negative correlation with MPTA (r=-0.240 and -0.250). Sex (P=0.005), medial K-L grade (P=0.002), mTFA (P<0.001), MPTA (P=0.036), and AJLO (P<0.001) were significantly associated with the positive KAM-time integral in the multiple regression analysis (R2=0.1917) whereas the maximum KAM had significant association (R2=0.1843) with mTFA (P<0.001) and AJLO (P<0.001). When grouped according to the mechanical alignment by the interval of 1°, lower extremities with 3° to 8° of varus had greater positive KAM-time integral and maximum KAM values than those with 0° to 5° of valgus. However, within groups of 0° to 5° of valgus, there were no significant differences in the KAM values.

Conclusion

We found that mTFA and AJLO were the main explanatory variables for both the positive KAM-time integral and the maximum KAM. This study suggests that, dynamically, the varus must be corrected to at least neutral alignment during HTO, but valgus overcorrection does not further reduce the KAM.