The purpose of this study was to visualise the locus of the dynamic loading axis on the knee joint, and to evaluate changes in this locus during gait after high tibial osteotomy (HTO) in three patients who underwent HTO for medial compartment osteoarthritis (OA) of a varus knee. The bone structure of the lower limb and the relative position of skin markers were acquired from CT images. Motion capture data was acquired using spherical skin markers. Skeletal model movement during gait was calculated based on the movement of the markers. The locus of the dynamic loading axis on the knee joint was defined as the point on the proximal tibia joint surface that intersected with the loading axis of the lower limb, which passed through the centre of the femoral head and the centroid of multiple points surrounded by the distal tibia joint surface contour. This system was able to visualise the locus of the dynamic loading axis on the knee joint and not only lateral but also anterior-posterior direction movement. After HTO, the locus shifted from a medial and posterior area of the medial joint edge of the knee to a central area of the knee joint surface. This indicates that HTO shifted the dynamic loading axis. Lateral movement of the dynamic loading axis in the early stance phase of gait was reduced within a year after HTO.
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