Otolith function assessed with the subjective postural horizontal and standardised stance and gait tasks

Abstract

If otolith function is essential to maintain upright standing while moving along slanted or uneven surfaces, subjects with an otolith deficit should have difficulty judging whether the inclination of the surface on which they are standing is tilted or not. We tested this judgement and compared it with the ability to control trunk sway during standardised stance and gait tests. Thirteen patients with unilateral vestibular nerve neurectomy at least 6 months prior to testing and 39 age-matched controls were asked to move a dynamic posturography platform on which they were standing back to their subjective 'horizontal' position after the platform had been slowly tilted at 0.4 degrees/s to 5 degrees in 8 different directions. Normal subjects left the platform deviated in pitch (forwards-backwards) at about 0.7 degrees on describing the platform as levelled off for all directions of tilt. Patients showed larger deviations of about 1.3 degrees in pitch with significant differences for forward right tilt (1.58+/-0.73 degrees compared to 0.73+/-0.11 degrees for normals; mean and SEM) and for forward left. Roll (lateral) deviations were about 0.4 degrees for normals and 0.5 degrees larger for the patients (for example, for backward left, 1.13+/-0.24 degrees compared to 0.4+/-0.07 degrees in normals). Except for a tendency towards greater deviations to the lesion side of patients with eyes closed, no differences were noted between tests under eyes open and closed conditions. However, for backward and roll tilts patients needed to steady themselves first by grasping a handrail when tested with eyes closed. Stance tests on foam showed increases in roll and pitch trunk sway with respect to controls. Patients had significantly larger trunk roll sway deviations during 1-legged stance tests and during gait trials. For stance trials, the patients lost their balance control prior to the end of the standard 20-second recording time. We conclude that a unilateral loss of otolith inputs due to nerve resection permanently impairs the ability to judge whether the support surface is horizontal, and leads to excessive trunk sway when standing on a compliant surface as well as excessive trunk roll sway during gait.