Background In 3D gait analysis, the knee joint is usually expressed using the Eulerian description. It consists in breaking down the motion between the articulating bones of the knee into three rotations around three axes: flexion/extension, abduction/adduction and internal/external rotation. However, the definition of these axes is prone to error, such as the “cross-talk” effect, due to difficult positioning of anatomical landmarks. This paper proposes a post-hoc statistical correction method by principal component analysis (PCA), based on an objective kinematic criterion for standardization, in order to improve knee joint kinematics analysis.
Methods The method was applied to the 3D gait data of two different groups of three subjects (healthy and with knee osteoarthritis). Then, five indirect indicators of accuracy were computed (a) variance accorded to the 1st principal component; (b) range of motion of the varus-valgus during gait (c) Range of motion of the flexion/extension angle (d) preservation of the screw-home mechanism;(e) quantification of the symptomatic deformities in patients with knee osteoarthritis.
Results The first principal component accounted for almost 90% of the total data variance. The ab/adduction range of motion (ROM) was reduced from about 25° to 30° before, to less than 5° after reorientation, and the PCA led to about 7° more knee flexion/extension ROM. Additionally, the two internal rotation peaks were still time-aligned with the flexion/extension ones, according to the screw-home mechanism. Finally, the varus/valgus angle values after correction were much closer to the performed x-ray grading than before correction.
Conclusions The results showed that the correction eliminates the knee joint angle cross-talk effect, preserves the varus/valgus radiological deformation for patients with knee osteoarthritis and does not delete the knee screw mechanisms. These findings underline the fact that the proposed correction method produces new rotational axes that better fit true knee motion.
Disclosure of Interest None declared
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