Grasp Force Assistance via Throttle-Based Wrist Angle Control on a Robotic Hand Orthosis for C6-C7 Spinal Cord Injury

Individuals with hand paralysis resulting from a C6-C7 spinal cord injury (SCI) frequently rely on tenodesis for grasping. However, tenodesis generates limited grasping force and demands constant exertion to maintain a grasp, leading to fatigue and sometimes pain. We introduce the MyHand-SCI, a wearable robot that provides grasping assistance through motorized exotendons. Our user-driven device enables independent, ipsilateral operation via a novel control method, Throttle-based Wrist Angle (TWA), that allows users to maintain grasps without requiring continued wrist extension. A pilot case study with a person with C6 SCI shows an improvement in functional grasping and grasping force, as well as a preserved ability to modulate grasping force while using our device, thus improving their ability to manipulate everyday objects. This research is a step towards developing effective and intuitive assistive devices for individuals with hand impairments after SCI.

I. Introduction

A spinal cord injury (SCI) often results in partial or complete sensorimotor loss in the arms and lower body, leading to reduced functional independence. Restoration of hand function is one of the highest priorities for SCI populations [1]. Individuals with hand paralysis caused by SCI at the C6-C7 level often have preserved active wrist extension, which allows them to use a compensatory grasp pattern called tenodesis. Tenodesis leverages wrist extension to passively shorten the digit flexor tendons to close the hand, achieving some degree of thumb-finger lateral grip or finger flexion for grasp. However, the grasp forces generated through tenodesis often fall short of what is required for many activities of daily living (ADLs), even after surgical intervention [2]. In addition, constantly exerting wrist effort to maintain tenodesis can be uncomfortable or even painful to sustain for prolonged periods of time.