Functional principal component analysis reveals distinct kinematics changes between osteoarthric and healthy knees

It is important to understand the kinematics of deep knee flexion due to the difficulty patient have performing this activity. bfPCA can describe variability across the entire movement cycle and also identify patterns which a-priori feature identification cannot. The aim of this study was to use to compare the joint kinematics between knee OA and healthy during deep flexion using bfPCA. Six-degree-of-freedom (DoF) kinematics of deep kneeling were measured by registering a 3D-static CT onto 2D-dynamic fluoroscopic images. bfPCA was undertaken on all DoF as a function of flexion. Superior-inferior position modes showed OA knees had reduced flexion, reduced gap between the femur and tibia and translated in a more superior direction compared to healthy. Internal/external rotation modes showed OA knee displayed reduced maximal flexion, maintained a more externally rotated position and underwent less overall change.