Temporal couplings between rearfoot–shank complex and hip joint during walking

BackgroundRearfoot pronation–supination and hip internal–external rotation are commonly assumed to be temporally coupled. Many mechanisms of musculoskeletal injury are proposed based on this assumption. Previous studies suggested that this theoretical coupling does not exist. However, recent experimental studies observed relationships consistent with foot–hip mechanical interdependence.MethodsThree-dimensional kinematics of the lower extremity of 18 healthy subjects, wearing flat trekking sandals, was measured during the stance phase of normal walking. Rearfoot–shank complex motion in the transverse plane (shank internal–external rotation) and frontal plane (rearfoot eversion–inversion) and hip motion in the transverse plane were analyzed. Cross-correlation coefficients were calculated to investigate temporal similarities between curves of rearfoot–shank and hip motions. Pearson correlations were used to investigate relationships between the timings of the peaks of these motions.FindingsCross-correlations revealed a strong mean temporal coupling (mean r = 0.77, range 0.56 to 0.92) between shank internal–external rotation and hip internal–external rotation and a moderate mean temporal coupling (mean r = 0.56, range 0.37 to 0.78) between rearfoot eversion–inversion and hip internal–external rotation. Pearson correlations revealed significant (P ≤ 0.031) moderate relationships of timing of peak shank internal rotation (r = 0.45) and timing of peak rearfoot eversion (r = 0.62) with timing of peak hip internal rotation.InterpretationThe findings suggest a temporal coupling of rearfoot pronation with hip internal rotation and rearfoot supination with hip external rotation during walking stance. The between-subjects variability of curves' temporal similarities and the moderate relationships between timings of motion peaks indicate that coupling strength should be clinically addressed on an individual basis.