Three-dimensional analysis of locomotion patterns after hindlimb suspension and subsequent long-term reloading in growing rats.

The long-term effects of insufficient weight loading during growth on locomotion patterns are not fully understood. The purpose of this study was to determine 1) the effects of hindlimb suspension (HS) in skeletally immature rats on locomotion patterns using a treadmill and a three-dimensional (3D) motion analysis system, and 2) the relationships between locomotion patterns and femoral morphologies, which were reconstructed from 3D computed tomography images taken at 54 weeks old. Four-week-old female rats were subjected to HS four or eight weeks, followed by reloading for until reaching up to 54 weeks old. Age-matched untreated rats served as controls. Motion analysis revealed that four and/or eight weeks of HS resulted in increased pelvis oscillation in the frontal plane during steps, decreased hip adduction angle, and toe-out (increased foot abduction angle) during the load response phase at one and five weeks after reloading. Interestingly, the decreased hip adduction angle and toe-out induced by eight weeks of HS persisted even at 54 weeks old. Pearson's correlation analysis revealed a strong relationship between the hip adduction angle and femoral anteversion angle (r = -0.78) and a moderate relationship between the medial/lateral condyle height (an index of asymmetric condyle size) and toe-out angle (r = 0.66). These results suggest that insufficient weight loading during growth may induce abnormal locomotion patterns via abnormal femoral morphologies that may persist over time.