Relationship between thoracic alignment asymmetry and hip joint alignment during isometric hip rotation: a comparison of femoral head deviation between left and right sides

[Purpose] We aimed to investigate the relationship between thoracic alignment asymmetry and side-to-side differences in femoral head deviation. [Participants and Methods] Twenty-six healthy adults participated in this study. We used three-dimensional motion analysis and ultrasonography to measure changes in femoral head deviation during isometric hip rotation and examine the relationship between thoracic alignment asymmetry and side-to-side differences. [Results] We observed that the femoral head deviated anteriorly during external rotation and posteriorly during internal rotation. At rest, the femoral head showed greater anterior deviation on the left side compared to the right. Task-induced femoral head deviation changes were greater on the right during external rotation and greater on the left during internal rotation. Moreover, we observed a positive correlation between the lower thoracic shape asymmetry and resting femoral head deviation. [Conclusion] Our findings suggest that lower thoracic asymmetry is associated with side-to-side differences in resting femoral head deviation and is potentially mediated through kinematic chain interactions.