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

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 biomechanical basis for abandoning the overcorrection is lacking. From a dynamic perspective, medial-to-lateral knee joint load distribution during gait can be reflected by knee adduction moment (KAM), and the main purpose of HTO is to reduce the KAM increased during gait due to varus alignment. We tried to reveal the association between the KAM obtained from three-dimensional 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. When grouped according to the alignment by the interval of 1°, lower extremities with 3° to 8° of varus had greater KAM values than those with 0° to 5° of valgus. However, within groups of 0° to 5° of valgus, there were no significant differences. Therefore, the varus must be corrected to at least neutral alignment during HTO, but valgus overcorrection does not further reduce the KAM.