Three-dimensional analysis of human locomotion in normal subjects and patients with vestibular deficiency.

The purpose of this study was to clarify the role of the vestibular system in human locomotion. The subjects were nine healthy controls, nine patients with unilateral vestibular deficiency (UVD) and nine patients with bilateral vestibular deficiency (BVD). The UVD subjects were Ménière's disease patients who were being treated with administration of gentamicin into the tympanic cavity. BVD subjects were hearing-impaired individuals who showed no response to the ice-water caloric test. A total of 13 markers were attached to the head, trunk (C7), hip and foot in order to measure translational and rotational motions with the aid of a video image processing system. All subjects were instructed to restrict their stride length to approximately 80 cm while walking on a treadmill and watching a visual target. However, walking speed varied depending on the ability of the subject to maintain body equilibrium. The results showed that walking speed and step frequency were significantly lower for the UVD and BVD groups than for the normal group. Analysis of head movements in the sagittal plane showed a counteracting motion between pitch rotations and vertical translation as previously reported. We also found head counteracting motions between yaw rotation and lateral translation in the horizontal plane. These mechanisms are thought to help stabilize the gaze during walking. When the head fixation point was calculated by projecting the naso-occipital axis line during walking, the head counteracting motion was found to assist the vestibulo-ocular reflex in stabilizing the gaze. In addition, normal subjects seemed to use head stabilization as a space strategy in order to minimize head yaw movement. In contrast, UVD and BVD subjects adopted head stabilization as a trunk strategy.