Stability limits for visual feedback posturography in vestibular rehabilitation

Vestibular rehabilitation therapy (VRT) is used to enhance compensation after peripheral vestibular lesion. In visual feedback posturography (VFP) a patient can practice postural control actively on a force platform and progress in the VRT can be objectively measured. The aim of the study was to determine normative values for stability limits (SL) in the VFP. Eleven healthy subjects were measured with force platform in visual feedback condition. Subjects were instructed to move their center of gravity (COG) marker to given targets, which were displayed on a computer screen in front of them. Target distance from the center of the platform was increased step by step to determine the SL in 8 directions. Hit delays (HD) to the targets and hold percentages (HP) within the targets were measured to quantify the difficulty of the individual targets as a function of subject's shoe size. With fixed feet position the SL in anterior direction increased 1.2 times the absolute increase in shoe length. An almost similar increase was found in anterolateral direction. The knowledge of the mechanical SL is important, because targets near SL should be avoided for safety reasons.