SYNERGISTIC MOMENTS AT THE HIP AND KNEE JOINTS ARE ALTERED IN POST-STROKE HEMIPLEGIC GAIT

摘要

Following stroke, many patients are unable to adequately bend their knee during the swing phase of gait [1,2]. This loss of functional control may be related to an abnormal muscle synergy or torque couple in the lower limb, similar to those reported for the upper extremity [3-5]. For example, several investigators have described a flexor synergy that couples shoulder abduction torque and elbow flexion torque under static, isometric conditions [3-4]. This couple is typically altered following stroke [3-4]. In the lower extremity, hip kinetics in the frontal plane appear to be coupled with knee kinetics in the sagittal plane for static, isometric conditions [6]. It is unknown, however, whether the same relationship holds for hip and knee kinetics under dynamic conditions, such as during the swing phase of gait. Identification of abnormal joint torque synergies during swing is likely to have implications for gait rehabilitation in post-stroke hemiplegia. For example, it is possible that patients increase hip abduction during swing because they often compensate for stiff-knee gait by hip hiking (increased pelvic obliquity) and circumduction of their impaired limb [1,2]. These mechanical adaptations have been shown to be successful at improving such aspects of gait as independence, weight support, and walking speed, yet they appear to occur without a change in abnormal muscle activation patterns in the lower limb [2]. This suggests that the development of therapeutic strategies that target abnormal muscle synergies at the hip and knee joint might lead to greater improvements in gait function over conventional therapy. Such techniques have already been shown to be effective in the upper extremity [4]. The purpose of this study was to investigate the relationship between voluntary hip abduction torque and secondary torque at the knee joint during the swing phase of gait in both chronic stroke patients and healthy control subjects. To date, no one has investigated the presence of across-joint torque associations under dynamic conditions in the lower extremity.