Biomechanical Modeling of Tendon Transfer in Tetraplegia

Principal Investigator: Wendy M. Murray, PhD

Investigators: Garry E. Gold, MD; Vincent R. Hentz, MD; M. Elise Johanson, MS, PT; Zoia C. Lateva, PhD; Kevin C. McGill, PhD; Niels Smaby, PhD; and Anca Velisar, MS

Project Category: Spinal Cord Injury - 2005

Objective: This study will attempt to develop better biomechanical models for predicting the outcome of brachioradialis-to-flexor-pollicis-longus (Br-FPL) tendon transfer, a procedure that restores lateral pinch following tetraplegia. We hypothesize that the effectiveness of the transferred brachioradialis is impaired because of post-operative muscle adaptations and weakness of elbow and wrist extensors. The specific aim of this study is to characterize the structural and functional changes that take place in transferred muscle, and to more accurately model the impairments associated with the surgically altered tetraplegic limb.

Research Plan: This project has four specific aims:

Aim 1: A computer simulation of the Br-FPL transfer will characterize the clinical ideal, in which the transferred muscle has normal strength and is maximally activated for its new function.

Aim 2: The nominal model will be personalized to represent 8-10 surgical candidates based on pre-operative assessments of Br cross-sectional area obtained from medical imaging, and elbow and wrist extension strength.

Aim 3: The transferred Br will be re-imaged and a novel electrophysiological technique will be applied in the same subjects who were studied pre-operatively to identify post-operative changes to muscle and fiber architecture.

Aim 4: The ability to fully activate the transferred Br during lateral pinch will be quantified in the same subjects. The personalized simulations will be further refined based on the data collected in Aim 3.

Work Accomplished: Eight subjects were enrolled; two additional candidates are scheduled for surgery and are willing to participate. A kinematic model of the upper extremity was modified to facilitate the computer simulations. We used the model to estimate resting positions of the elbow, forearm, and wrist concomitantly under passive conditions, with the limb in different orientations relative to gravity, and with the fingers and thumb in different functional postures. We established two computational strategies to alter the model to represent the passive joint properties of the tetraplegic limb. In the next year, active function of the Br-FPL transfer and the elbow and wrist extensors will be added to the simulations completed under passive conditions. These simulations will allow a comparison of the maximum potential of the transfer to generate force given the assumptions of the clinical ideal to the maximum force produced given the limitations in strength identified from the pre-operative data.

This work will identify and characterize which factors need to be incorporated into a biomechanical model to accurately predict surgical outcome of the Br-FPL transfer. In doing so, the factors responsible for disappointing surgical outcomes will be better understood, which will lead to better treatment decisions.

Funding Source: NIH

Funding Status: Active