Functionally Oriented Alignment of the Lower Extremity Reflecting the Direction of Gait for Healthy Elderly, Knee Osteoarthritis, and Total Knee Arthroplasty Subjects

Purpose The objective of this study was to evaluate the functional lower extremity alignment based on both position and motion [functionally oriented alignment (FOA)] of the knee in healthy elderly, varus osteoarthritis (OA), and total knee arthroplasty (TKA) subjects. Methods This study evaluated 87 knees in 24 healthy elderly (72 +/- 5 years), 39 varus OA (72 +/- 6 years), and 24 TKA (75 +/- 4 years) subjects. A 3D assessment system was used on 3D models and biplanar long-leg radiographs with the toe angle reflecting gait direction, by applying a 3D-to-2D image registration technique. In the world coordinate system, they-,z-, andx-axes were defined as gait direction, gravity direction, and the cross product ofy- andz-axes, respectively. The parameters were: (a) coronal inclination, sagittal inclination, and transverse direction of the femur and tibia relative to the ground and (b) the difference between theyz-plane of the world coordinate system (functional plane) and theyz-plane of the femoral or tibial coordinate system (anatomical plane). Results The femur had more medial and posterior inclination and the tibia had more lateral and anterior inclination in osteoarthritic knees as compared to healthy knees, and TKA knees had inclinations similar to healthy knees. Rotation was similar or different in the anatomical and functional planes among the subjects with the healthy, knee OA, and TKA. Conclusions The association between the anatomical and functional planes and the position of each bone relative to gravity varied depending on the condition of the knees. Level of Evidence: Level of III