Kinematic analysis of the hip and trunk during bilateral stance on firm, foam, and multiaxial support surfaces.

OBJECTIVE To differentiate hip and trunk motion during double-leg stance. DESIGN Trunk and hip angular position variances were measured on different support surfaces with and without vision. BACKGROUND Postural control results from motion about the hips and trunk during bilateral stance. While the hip joint has been studied extensively, information concerning relative amounts of hip and trunk motions during postural control is limited. METHODS Trunk flexion/extension, trunk lateral flexion, right and left hip flexion/extension and abduction/adduction angular position variances were assessed in 14 normal subjects using an electromagnetic tracking system during bilateral stance on firm, foam, and multiaxial support surfaces with and without vision. RESULTS Significantly greater amounts of motion occurred at all joints for the multiaxial-eyes closed condition compared to all other surface-vision conditions. No significant differences were found between any other surface-vision conditions. Within the multiaxial-eyes closed condition, right and left hip flexion/extension and abduction/adduction magnitudes were significantly greater than those of trunk flexion and lateral flexion, and left hip flexion/extension motion was significantly greater than that of the right hip. CONCLUSIONS Postural control mechanisms involve similar amounts of motion at the hips and trunk, except for conditions under which a rigid base of support becomes unstable and vision is eliminated. RELEVANCE These results suggest that the trunk and hips should be considered separately during kinematic analysis of postural control. This information may be useful in providing a more sensitive assessment of postural control to identify balance-related pathologies associated with stroke, concussion, and somatosensory deficits.