Functional Restoration of Grasp in Quadriplegia

Investigators: V. Rodney Hentz, MD and Felix E. Zajac, PhD

Project Staff: Francisco J. Valero-Cuevas, PhD, M. Elise Johanson, MS, PT, Inder Perkash, MD, Charles G. Burgar, MD, and H.F. Machiel Van der Loos, PhD

Collaborator: Kai-Nan An, PhD

Summary: Further advances in surgical reconstruction techniques for restoring hand function in quadriplegia will require a better understanding of the complex mechanical operation of the muscles that control the hand. The objective of this project is to develop and validate a computer model of the thumb and forefinger in grasping. The model will make it possible to optimize surgical procedures so that as much grasping function as possible is restored to the quadriplegic patient.

Problem: Developing rehabilitation strategies to restore grasping to persons with neurologic impairments is difficult, because the nervous system must coordinate many muscles to execute simple grasps.

Approach: Computer models of muscle coordination for static finger and thumb forces, like holding a key, let us discover the basic features of muscle coordination essential to motor task execution. By studying computer simulations of the biomechanics of static finger forces, we can determine, first, how the basic bomechanical features of the fingers determine muscle coordination patterns in grasping and, second, which muslces must be targeted for surgical or therapeutiic rehabilitation to restore grasping function. Experiments are conducted to validate our modeling results.

Experimental Work: We have used a biomechanical computer model and experimental tests to understand the muscle coordination of the index finger during grasping tasks. Our current objective is to understand the coordination of the muscles of the thumb during similar tasks.

We hope to us this approach to design better surgical reconstruction of hands of quadriplegics to improve their ability to grasp and manipulate objects.

Findings: Grasping an object requires the fingers to generate sufficiently high forces in specific directions. A 3D computer biomechanical model of the index finger has been developed. Fingertip forces while recording EMG signals from all the finger muscles have been recorded to validate the model. A model and similar experiments on the thumb are in progress. We found the excitation patterns producing fingertip force to be consistent across subjects and robust to fingertip force direction. Since the computer model of the index finger was able to reproduce almost all of the important features of these patterns, finger biomechanics dominates muscle coordination, as predicted. Based on these findings, modifications to tendon transfers for the quadriplegic hand have been proposed and data from cadaveric hands supports the computer modeling conclusions.

Related Work: Similar work is directed toward restoring lower extremity coordination and ambulation to neurologically impaired individuals.

Funding Source: VA RR&D Merit Review

Years: 1994-1999