Evaluation of dynamic knee joint alignment using a one-way frontal video method

Abstract

In clinical practice, motion analysis can be challenging due to lack of space. Therefore, we propose a method of using one-way frontal video that can be executed easily in a small area. As it has been suggested that gait analysis using one-way frontal video can be used to analyze dynamic changes to knee joint alignment, the purpose of this research was to evaluate this method of motion analysis and examine the accuracy of this technique compared with that of a 3D motion analysis system. Twelve healthy subjects wearing optical reflective markers participated in this gait analysis study that involved the simultaneous use of one-way frontal video and a 3D motion analysis system. The femoral tibial angle (FTA) and the distance between the lower limb mechanical axis and the center of the knee joint were analyzed. The mean absolute error (MAE) of the results from the one-way frontal video and the 3D motion analysis system was calculated and the accuracy of the one-way frontal video method was evaluated. As a result, the patterns of change in knee alignment index obtained from the one-way frontal video all qualitatively matched those observed using the 3D motion analysis system. The MAE was 0.8 degrees in the FTA and the distance between the lower limb mechanical axis and the center of the knee joint was 2.5 mm. The MAE of knee joint alignment was sufficiently small compared to the alignment change associated with abnormal motion in patients with osteoarthritis. Therefore, the evaluation of knee joint alignment using the one-way frontal video method offers sufficient levels of accuracy to be used in diagnoses of abnormal movement.