Abstract
BackgroundStroke patients have impaired postural balance that increases the risk of falls and impairs their mobility. Assessment of postural balance is commonly carried out by recording centre of pressure (CoP) displacements, but the lack of data concerning reliability of these measures compromises their interpretation. The purpose of this study was to investigate the between-day reliability of six CoP-based variables, in order to provide i) reliability data for monitoring postural sway and weight-bearing asymmetry of stroke patients in clinical practice and ii) consistent assessment method of measurement error for applications in physical medicine and rehabilitation.MethodsPostural balance of 20 stroke patients was assessed in quiet standing on a force platform, in two sessions, 7 days apart. Six CoP-based variables were collected in eyes open and eyes closed conditions: postural sway was assessed with mean and standart deviation of CoP-velocity, CoP-velocity along the mediolateral and anteroposterior axes, and confidence ellipse area (CEAREA); weight-bearing asymmetry was assessed with mean CoP position along the mediolateral axis (CoPML). The intraclass correlation coefficient (ICC) was used to determine the level of agreement between test-retest. Small real difference (SRD), corresponding to the smallest change that indicates a real improvement for a single individual, was used to determine the extent of measurement error.ResultsICCs were satisfactory (>0.9) for all CoP-based variables, except for CEAREA in eyes open condition and CoPML (<0.8). The SRDs (eyes open/closed conditions) were: 6.1/9.5 mm.s-1 for mean velocity; 12.3/12.2 mm.s-1 for standard deviation of CoP-velocity; 3.6/5.5 mm.s-1 and 4.9/7.3 mm.s-1 for CoP-velocity in mediolateral and anteroposterior axes, respectively; 17.4/21.4 mm for CoPML. Because CEAREA showed heteroscedasticity of measurement error distribution, SRD (eyes open/closed conditions) was expressed as a percentage (121/75%) and a ratio (3.68/2.16) obtained after log-antilog procedure.ConclusionsIn clinical practice, the CoP-based velocity variables should be prefer to CEAREA to assess and monitor postural sway over time in hemiplegic stroke patients. The poor reliability of CoPML compromises its use to assess weight-bearing asymmetry. The procedure we used could be applied in reliability studies concerning other CoP-based variables or other biological variables in the field of physical medicine and rehabilitation.
Highlights
Stroke patients have impaired postural balance that increases the risk of falls and impairs their mobility
Many centre of pressure (CoP)-based variables have been proposed in the literature, we focused on six of them that have already been studied and demonstrated their relevance in hemiplegic stroke patients [8,10,11,12,13,14,15,17,19,35]: mean and standard deviation of resultant CoP velocity (VEL and Standard deviation of resultant CoP velocity (SDVEL), respectively, in mm.s−1), mean velocity of CoP along the mediolateral and anteroposterior axes (VELML and VELAP, respectively, in mm.s−1), area of the 90% confidence ellipse enclosing CoP (CEAREA in mm2), and absolute value of the mean CoP position along the mediolateral axis (CoPML in mm)
In the presence of heteroscedasticity of random error distribution, we determined the extent of measurement error using ratio and tested the use of measurement error expressed as percentages
Summary
Stroke patients have impaired postural balance that increases the risk of falls and impairs their mobility. The purpose of this study was to investigate the between-day reliability of six CoP-based variables, in order to provide i) reliability data for monitoring postural sway and weight-bearing asymmetry of stroke patients in clinical practice and ii) consistent assessment method of measurement error for applications in physical medicine and rehabilitation. Stroke patients have postural balance impairments that result in increased postural sway and weight-bearing asymmetry in quiet standing, that is commonly carried out by recording centre of pressure (CoP) displacements with a force platform [6,7,8,9,10,11]. Many reliability studies have focused on healthy subjects [25,26,27,28,29,30], or patients with different levels of disequilibrium [31,32], but no study has and comprehensively investigated the test-retest reliability of CoP-based variables in quiet standing for hemiplegic stroke population
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