Tenodesis Grasp Emulator: Kinematic Assessment of Wrist-Driven Orthotic Control

Abstract

Wrist-driven orthotics have been designed to assist people with C6-7 spinal cord injury, however, the kinematic constraint imposed by such a control strategy can impede mobility and lead to abnormal body motion. This study characterizes body compensation using the novel Tenodesis Grasp Emulator, an adaptor orthotic that allows for the investigation of tenodesis grasping in subjects with unimpaired hand function. Subjects perform a series of grasp and release tasks in order to compare normal (test control) and constrained wrist-driven modes, showing significant compensation as a result of the constraint. A motor-augmented mode is also compared against traditional wrist-driven operation, to explore the potential role of hybrid human-robot control. We find that both the passive wrist-driven and motor-augmented modes fulfill different roles throughout various tasks tested. Thus, we conclude that a flexible control scheme that can alter intervention based on the task at hand holds the potential to reduce compensation in future work.

A Grasp Taxonomy for People with C5-7 Spinal Cord Injury

“…Given this wide range of behaviors and contact points, we assert that it is imperative to critically evaluate how a proposed assistive device for ADLs might unintentionally inhibit any of these strategies, and how the device makes up for this. For example, a hand exoskeleton, such as one that aims to improve prehensile grasping, e.g., [31], that covers the dorsal side of the hand may hinder the use of strategies involving it, such as the dorsal support, push, and hook nonprehensile strategies. New product features may emerge from this taxonomy framework, such as more emphasis on the profile, robustness, and contact friction of hardware that is not located on the palmar side of the hand.…”

The Supernumerary Dorsal Grasper for people with C5-C7 spinal cord injury

“…Although these surgeries have shown positive results, they are nonetheless underutilized [20], [21]. On the other hand, wearable assistive orthotics provide a practical non-invasive pathway to improve daily function [22] as well as enabling rapid prototyping for early studies on normative populations [23].…”

“…Rigid exoskeletons benefit from a precise analysis of power transmission to various joints. One common device is the wrist-driven orthosis (WDO) with a mechanical linkage to enhance tenodesis grasping [11], [12]. However, difficulties associated with these devices include comfort and fitting to different individuals [27], [28].…”

“…Tenodesis grasp allows for picking up light and small objects, however it is less suitable for heavier and larger ones [9]. In addition, compensatory strategies like tenodesis grasp may lead to overuse injury [10] and limit the reachable workspace [11]. For heavier and larger objects, bimanual manipulation is often used, however, this limits the workspace even further.…”