Kinematic characteristics of standing disequilibrium: Reliability and validity of a posturographic protocol

Objective: To investigate retest reliability and concurrent validity of the fundamental measurements made of a posturographic protocol that employs quiet standing to quantify the severity and the nature of patients' postural disturbances. Study Design: Retrospective complete block design. Setting: Geriatric rehabilitation department. Participants: Thirty-six participants (age range, 67 to 86yrs) having normal, moderate, or severe levels of disequilibrium. Methods: Quiet standing was evaluated on three occasions using a three-dimensional motion analysis system and a force platform. Eight testing conditions, designed to vary task difficulty by controlling the contributions of vision, foot proprioception, and base-of-support width, were administered. Main Outcome Measures: Retest reliability of body sway, joint alignment, body position, and motor coordination indicators were evaluated by intraclass correlation coefficients (ICCs). Concurrent validity of protocol measures was evaluated by the prediction of disequilibrium from a stepwise linear discriminant analysis. Results: ICCs indicated high level of retest reliability for all variables but those of motor coordination, which was not influenced by testing conditions. Discriminant analysis resulted in a four-factor discriminator that included measures of body sway, position, alignment, and motor coordination. The derived linear discriminate function correctly classified 96% of the patients' level of disequilibrium. Conclusions: The posturographic protocol has the potential to be a useful tool for evaluating severity and nature of postural instability and the effects of pharmacologic and rehabilitative treatment. Results also indicate that combining direct body measurements with force-plate data has the potential to expose the underlying impairments that cause disequilibrium, determine their pathogenesis, and evaluate compensatory strategies.