Hip sway associated with vestibulopathy

We identify a population of patients with vestibular complaints who show excessive hip sway and center of gravity movement during clinical balance testing. To determine the postural control strategy used by these patients, the body movement and muscle activation patterns of 9 patients responding to backward support surface translations were studied. Patients' responses were compared to those of normal subjects tested both under the same conditions and while using hip sway to balance across a narrow beam. Unlike normal subjects responding to translations of a flat support surface, all patients showed hip movement patterns that kinematically resembled the movements of normal subjects balancing across a beam. Although all patients showed the same body movement patterns, they showed two different muscle activation patterns, neither of which was similar to those of normal subjects responding to flat support surface translations. Four patients showed bursts in abdominal and/or quadriceps muscles characteristic of active hip flexion to move the center of mass, although the timing of these bursts was variable. The remaining 5 patients showed minimal activation of any proximal muscles, suggesting a failure to control upper body motion resulting from activation of ankle muscles. To determine whether the excessive hip sway observed in these patients could be a voluntary response to platform translation, the patients' responses were compared to those of a second group of normal subjects voluntarily responding to backward support surface translations with hip sway. Unlike the patients, all normal subjects responding voluntarily consistently activated abdominal muscles slightly later than ankle muscles. It is therefore unlikely that the patients' responses to platform translations were simply voluntary responses. Thus, vestibular deficits can result in abnormally coordinated postural movement strategies that result in excessive hip sway.