Use of visual force feedback to improve digit force direction during pinch grip in persons with stroke: A pilot study

Seo NJ, Fischer HW, Bogey RA, Rymer WZ, Kamper DG. Use of visual force feedback to improve digit force direction during pinch grip in persons with stroke: a pilot study. Objective To investigate whether visual feedback of digit force directions for the index fingertip and thumb tip during repeated practice of grip force production can correct the digit force directions for persons with stroke during grip assessments. Following stroke, the paretic fingers generate digit forces with a higher than normal proportion of shear force to compression force during grip. This misdirected digit force may lead to finger-object slip and failure to stably grasp an object. Design A case series. Setting Laboratory. Participants Persons (N=11) with severe chronic hand impairment after stroke. Interventions Four training sessions during which participants practiced directing the index finger and thumb forces in various target directions during pinch using visual feedback. Main Outcome Measure Digit force direction during pinch and clinical hand function scores were measured before and immediately after the training. Results Study participants were able to redirect the digit force closer to the direction perpendicular to the object surface and increase their hand function scores after training. The mean ratio of the shear force to the normal force decreased from 58% to 41% (SD, 17%), the mean Box and Block Test score increased from 1.4 to 3.4 (SD, 2.0), and the mean Action Research Arm Test score increased from 10.8 to 12.1 (SD, 1.3) (P<.05 for all 3 measures). Conclusions Repeated practice of pinch with visual feedback of force direction improved grip force control in persons with stroke. Visual feedback of pinch forces may prove valuable as a rehabilitation paradigm for improving hand function.