Effect of Carpal Tunnel Syndrome on Trial-to-Trial Adaptation to Object Mass-Sensorimotor Integration for Multi-Digit Grasping

Abstract

Introduction/Objective: Somatosensory feedback from the fingertips is integrated with voluntary control of hand muscles in order to successfully grip objects. This integration can be disrupted in Carpal Tunnel Syndrome (CTS) and lead to dropping objects. This raises the question of how the central nervous system (CNS) integrates sensory information from CTS-affected and non-affected digits. The primary objective was to use CTS as a model to understand mechanisms underlying sensorimotor integration responsible for whole-hand griping of objects with a changing mass. CTS patients should be able to modulate digit forces to object weight, however, as different grip types involve the exclusive use of CTS-affected digits or a combination of CTS-affected and non-affected digits, we hypothesize sensorimotor deficits to be larger for grips involving the coordination of CTS-affected and non-affected digits. Methods: Sixteen CTS patients (3 males, 13 females) and age- and gender-matched controls participated in the study. Subjects were instructed to use one of four grip types: two digits, three digits, four digits, or all five digits to grasp, lift, hold level and release a grip device for 7 consecutive lifts. Object mass was changed across blocks of trials by inserting either a “light mass” (445g) or a “heavy mass” (745g) underneath the grip device. Force and torque exerted by each digit were measured. Results: CTS patients learned multi-digit force modulation to object weight regardless of grip type. Although controls exerted the same total grip force across all grip types, patients exerted significantly larger grip force than controls but only for manipulations with four and five digits. Importantly, this effect was due to CTS patients’ inability to change the finger force distribution when adding the ring and little fingers. Significance: These findings indicate CTS primarily challenges sensorimotor integration processes underlying the coordination of CTS-affected and non-affected digits.