Agreement between measurements of stance width using motion capture and center of pressure in individuals with and without Parkinson’s disease

Abstract

BackgroundMany individuals with Parkinsons disease exhibit narrow stance width during balance and gait. Because of this, stance width is an important biomechanical variable in many studies. Measuring stance width accurately using kinematic markers in parkinsonian patients can be problematic due to occlusions by research staff who must closely guard patients to prevent falls.\n\nMethodsWe investigated whether a measure of stance width based on the mediolateral distance between the center of pressure under each foot could approximate stance width measured with kinematic data. We assessed the agreement between estimates of stance width obtained from simultaneous kinematic and center of pressure measures during quiet standing in 15 individuals (n=9 parkinsonian, n=6 age-similar neurotypical). The source data (1363 unique trials) contained observations of stance width varying between 75-384 mm ({approx}25-150% of hip width).\n\nFindingsStance width estimates using the two measures were strongly correlated (r = 0.98). Center of pressure estimates of stance width were 48 mm wider on average than kinematic measures, and did not vary across study groups (F2,12=1.81, P<0.21). The expected range of differences between the center of pressure and kinematic methods was 14-83 mm. Agreement increased as stance width increased (P<0.02).\n\nInterpretationIt is appropriate to define stance width based on center of pressure when it is convenient to do so in studies of individuals with and without Parkinsons disease. When comparing results across studies with the two methodologies, it is reasonable to assume a bias of 48 mm.