Influence of Axial Rotation Between the Femoral Neck and Ankle Joint on Kinematics in Normal Knees: A Cross-Sectional Study.

Background: The effect of axial rotation between the femoral neck and ankle joint (total rotation [TR]) on normal knees is unknown. Therefore, this study aimed to investigate the TR effect on normal knee kinematics.

Methods: Volunteers were divided into groups large (L), intermediate (I), and small (S), using hierarchical cluster analysis based on TR in the standing position. TR was measured using three-dimensional (3D) bone models generated from CT. A two-dimensional to 3-dimensional registration technique was used to assess the spatial position and femur and tibia orientation during squat. The axial rotation, varus-valgus alignment, and anterior-posterior translation of the femur relative to the tibia were evaluated.

Results: Group L had the highest TR, whereas group S had the lowest TR (L: 36.6° ± 6.0°, I: 23.2° ± 3.0°, and S: 13.8° ± 5.1°). Above 50° of flexion, femoral external rotation was greater in group S than in groups L and I. From 40° to 110°, the medial side was more anterior in group L than in groups I and S, whereas the lateral side was more posterior in group S than in groups L and I.

Conclusions: Individuals with larger TR had more femur anterior-medial translation relative to the tibia.