Association between the toe angle and bony factors in the transverse plane for osteoarthritic knees compared with healthy knees.

BACKGROUND The association between the toe angle and bony rotational factors is critical to explain issues related to the onset and progression of knee osteoarthritis (OA). OBJECTIVE The study aimed to clarify the association between the toe angle and each of the femoral and tibial transvers direction relative to gait direction, rotational knee alignment, and bony torsional deformity for the subjects with knee OA. METHODS This study evaluated 58 knees in 24 healthy elderly (72 ± 5 years) and 34 varus knee OA (72 ± 6 years). A three-dimensional (3D) assessment system was used on 3D models and biplanar long-leg radiographs with the toe angle reflecting gait direction, applying a 3D-to-2D image registration technique. The main parameters on the transverse plane were: (1) toe angle, (2) transverse direction of the femur and tibia relative to the gait direction, (3) femoral neck anteversion, (4) condylar twist angle, (5) tibial torsion, and (6) rotational knee alignment. RESULTS The alignment parameters, except for the tibial transverse direction, were different between healthy and osteoarthritic knees. In knee OA, the femoral neck anteversion - femoral transverse direction (p = 0.001), femoral transverse direction - tibial transverse direction (p < 0.001), and tibial transverse direction - toe angle (p < 0.001) were associated. CONCLUSIONS The osteoarthritic knees showed that the femoral neck anteversion was associated with the femoral transverse direction, which determined the tibial transverse direction by adjusting the rotational knee alignment, leading to the toe angle.