Objective Measures of Hand and Finger Strength

Chronic Trauma Disorder Prevention

Introduction

Chronic Trauma Disorders (CTDs) are now a major cause of disability. CTDs occur when the forces acting on the body repeatedly exceed its functional capacity resulting in musculoskeletal, vascular or neural abnormalities. Traditionally, CTD prevention and treatment has focused on decreasing limb use which limits functional independence, particularly among wheelchair users.

The goal of this research is to investigate the benefits of increasing the functional capacity of the limb to maintain use within the limb\'s functional capacity. Strength training, which improves movement efficiency, increases bone density and strengthens muscles, tendons and ligaments, would increase the limb\'s functional capacity and allow the limb to meet increased demands without inducing microtrauma to the tissues.

Current assessments of hand strength use hand grip and pinch dynamometers which measure limited hand movements, are unable to measure the forces specific to a variety of hand functions, provide gross measures of strength rather than isolated forces for each digit or joint and cannot assess the extension musculature. As such, they are unable to provide a comprehensive strength assessment of the fingers, hand, wrist and forearm.

Research Objectives

The purpose of this project was to develop devices to provide quantitative measures of isometric wrist, hand and finger strength as well as the grip strength on a wheelchair pushrim. Measures of individual joints or digits, gross measures of pinch and hand grip, assessment of opposing joint motions, and suitability for clinical rehabilitation were incorporated into the designs.

Four prototype devices were proposed to complete the required measurements:

Hand strength assessment device (HSAD): flexion and extension of isolated MCP and PIP joints;

Image of HSAD

Pushrim grip assessment device (PGAD): grip strength on wheelchair pushrim;
Image of PGAD

Multi-finger assessment device (MFAD): flexion and extension of all fingers at MCP or PIP joints; and
Image of MFAD

Wrist strength assessment device (WSAD): flexion/extension, pronation/supination, radial/ulnar deviation of wrist.
Image of WSAD flexion/extension

Image of WSAD radial/ulnar deviation

Image of WSAD pronation/supination

The designs were evaluated using models and simple prototypes, and then working prototypes were evaluated for safety (static strength, fatigue).

Methods

Twenty-seven subjects (4 female, 23 male) completed the validity and/or reliability testing. Subjects without disabilities were selected as age (+/- 5 yrs) and gender matched controls for the subjects with disabilities. Subjects, recruited through clinics and the community, were primarily male, white, independent in activities of daily living and relatively fit and active.

Device validity was evaluated through comparisons to existing measures of hand strength (handgrip and pinch dynamometry). Repeat assessments were used to determine reliability and the potential influence of subject characteristics (e.g. gender, age) was considered.

Results & Discussion

The results indicated that the PGAD, MFAD, and WSAD devices provide valid and reliable measures of isometric strength for diverse subject groups (e.g. males and females, with and without CTDs). The HSAD did not provide sufficiently reliable and valid results, probably due to insufficient standardization of joint positioning.

The PGAD, MFAD and WSAD devices provide objective measures of agonist and antagonist musculature of the hand, wrist and forearm. The devices are ready for commercialization, are suitable for use in a clinical rehabilitation setting, and are acceptable to subjects in terms of comfort, time required and ease of use.

Further refinement of the devices will enhance their suitability for use in clinical rehabilitation programs. Use of these devices in future research will enable evaluations of the relationship between joint strength and overuse injury and/or the impact of training/rehabilitation programs.

Acknowledgment

This work was funded by the National Center for Medical Rehabilitation Research in the National Institute of Child Health and Human Development at the National Institutes of Health through Small Business Innovation Research Phase I Grant #1 R43 HD33940-01.