Posturographic description of the regaining of postural stability following stroke

Abstract

Failing balance and increased liability to falling are common complaints among hemiplegic subjects. During rehabilitation much effort is put into regaining postural stability. To describe the regaining of postural stability during rehabilitation for the first year following stroke in hemiplegic patients Twenty-six patients were included within 5 days of suffering a stroke resulting from a CT-verified clearly defined thromboembolic lesion, localized in the vascular bed of middle cerebral artery on either side. Posturographic evaluation of sway was performed on a commercially available force plate system (Balance Master Pro). Measured parameters included per cent maximum stability (PMS), per cent ankle strategy (AST), and average angular velocity (AVE). An additional parameter was derived by calculating the slope (SLP) of the linear relationship between stability and ankle strategy. SLP reflects the predisposition of the stroke patient to keep using ankle strategy when faced with increasingly difficult balance tasks. The presence of familiarization to the measurement method was examined by including a preliminary measurement not otherwise included in the analysis of changes during the first year of follow-up. The temporal evolvement of sway was described by measuring sway parameters 1, 2, 4, 8 and 52 weeks following stroke. The proportions of the variation in sway caused by measurement error and between patients were compared. All parameters improved over time, as demonstrated by significant improvements from each of week 1, 2, 4 and 8 to week 52. There was evidence of familiarisation for PMS, AST and AVE, but not for SLP. Estimation of variance components showed that between patient variation accounts for between two-thirds and four-fifths of the total variation. A considerable part of this variation was caused by individual differences in the temporal improvement of sway over time. Patients considered the evaluation of postural sway demanding and time consuming resulting in a relatively large loss to follow-up: 15 patients completed the 8-week visit while seven completed the 1 year visit. Postural stability increases for the first year following stroke. There is evidence of familiarization towards the measurements process for the traditional posturographic parameters PMS, AST and AVE, but not for the derived parameter SLP, which might make the latter a candidate for a sway parameter reflecting basic mechanisms of upholding upright stance in hemiplegic patients. The estimated variance components stress the considerable between-patient variation and question the ability of the force plate method to monitor individual sway performance of such patients during the rehabilitation process.