Impaired Discrimination of Surface Friction Contributes to Pinch Grip Deficit After Stroke

Abstract

Background. Impaired sensation and force production could both contribute to handgrip limitation after stroke. Clinically, training is usually directed to motor impairment rather than sensory impairment despite the prevalence of sensory deficit and the importance of sensory input for grip control. Objective. The aim of this study was to investigate if sensory deficits contribute to pinch grip dysfunction beyond that attributable to motor deficits poststroke. Methods. The study enlisted 45 stroke participants and 45 healthy controls matched for age, gender, and hand dominance. Ability to differentiate surface friction (Friction Discrimination Test [FDT]), match object weight (Weight Matching Test [WMT]), produce grip force to track a visual target (Visually Guided Pinch Test [VGPT]), and perform a Pinch-Grip Lift-and-Hold Test (PGLHT) was quantified relative to normative performance, as defined by matched controls. The relationship between sensory ability (FDT, WMT) and altered PGLHT performance adjusted for motor ability (VGPT) after stroke was then examined using multivariate regression. Results. Deficits in FDT, WMT, and VGPT ability were present in at least half of the stroke sample and were largely independent across the variables. Poorer friction discrimination was significantly associated with longer latencies of grip-lift ( r = .34; P = .03) and grip force dysregulation ( r= .34; P= .03) after the impact of VGPT was statistically removed from PGLHT ability. However, performance on WMT did not relate to either PGLHT deficit. Conclusion. The findings indicate that impaired friction discrimination ability contributes to altered timing and force adjustment during PGLHT poststroke.