The impact of centre of pressure error on predicted joint kinetics during cerebral palsy and typically developed gait: A clinical perspective.
Centre of Pressure (CoP) location error is common when using kinematic and kinetic data to predict intersegmental forces and net joint moments during gait. Changes in peak moments due to CoP error have been reported in the literature. However, debate exists as to what levels of error are acceptable. The aim of this study was to examine the impact of CoP error on the kinetic profiles of children with typical development (TD) and children with cerebral palsy (CP) during gait. Three-dimensional kinematic and kinetic data were recorded and simulated CoP errors were applied at 3 mm, 6 mm, 9 mm, 12 mm increments in both positive and negative anteroposterior and mediolateral directions. Absolute differences in maximum kinetic parameters between increments were assessed in conjunction with changes in the Gait Deviation Index-Kinetic (GDI-Kinetic). Changes in GDI-Kinetic above 3.6 points were considered clinically significant. Maximum peak changes of up to 24.8% (CP) and 34.7% (TD) (sagittal plane) and up to 36.8% (CP) and 61.5% (TD) (coronal plane) were demonstrated at the knee. While absolute percentage differences were high at some error increments, GDI-Kinetic results suggested that such large percentage differences may still be clinically acceptable. Children with TD demonstrated clinically significant changes in GDI-Kinetic for CoP displacements of 9 mm and 12 mm, corresponding to 23% and 35% absolute differences in maximum moments. In contrast, the clinically significant threshold was not reached for children with CP that may be related to a slower walking speed. The findings of this study highlight the need for laboratories to consider the thresholds currently used for CoP error, which will help guide quality assurance procedures.