Human head and body stability after unilateral vestibular loss

Ian Curthoys, Psychology, University of Sydney

Abstract
This study used simultaneous measures of human head and body movement to quantify the postural stability of healthy subjects and patients with vestibular loss. Head movement measures were obtained by a lightweight 6 degree of freedom movement sensor (MT9, Xsens, the Netherlands) attached to a tightly fitting headband which the subject wore on the head. We sought to derive fast, easy, objective measures of head stability and postural stability and to validate these measures by using them on patient groups whose postural performance is well established in order to verify that our measures and indices agreed with those well-established patterns. In the present study the movement of head and body of BVL and UVL patients as well as age-matched healthy control subjects were measured as each individual performed three standard computerized dynamic posturography tests in the presence or absence of visual information by standing on either: 1) a Satel platform with seesaw plate (Mbongo et al. 2005), or 2) a piece of 6 cm thick foam on a Satel platform or 3) a Synapsys platform which generated linear translations. The major results showed that UVL patients compensated over 1 year and that for many patients their pattern of head stability was similar to that of their postural stability across the tests. We confirmed that there were examples of different “stability styles” with some individuals showing greater head stability than body stability and others showing the opposite pattern. Measurement of head stability provides new and non-redundant information beyond that provided by postural measures. The RMS measures of head stability and body stability can, after normalization, be combined to yield a single postural performance score which is a new, objective, accurate way of quantifying a patient’s stability. These results have implications for diagnostic purposes as well as for rehabilitation after UVL.

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