Contribution of the extrinsic and intrinsic hand muscles to the moments in finger joints

Objective. The purpose of this current work is to develop a method of estimating force produced by the extrinsic and intrinsic hand muscles, and to estimate the contribution of these muscles to the finger joint moments. Design. Experimental methods and a biomechanical model were developed for the estimation of (a) moments produced at finger joints, and (b) contribution of the intrinsic and extrinsic muscles to the moments, (c) forces of the extrinsic and intrinsic muscles within individual fingers. Background. Because of the differential insertions of the extrinsic flexors, it is possible to isolate their mechanical effect at finger joints. Methods. During the experiment, the location of force application was varied in parallel along individual fingers. The points of force application were on the distal phalanx, at the distal interphalangeal joint, or at the proximal interphalangeal joint. Results. When the point of force application was varied in the proximal direction from the distal phalanx to the proximal interphalangeal joint the moment at a given joint decreased. The intrinsic and extrinsic muscle forces were dependent on the experimental conditions. The extrinsic muscles were the major contributors in counterbalancing finger joint moments when the point of force application was distal beyond the proximal interphalangeal joint. Conclusion. This current work provides both an experimental protocol and a biomechanical model that allows estimation of the contribution of the intrinsic and extrinsic muscles to finger joint moments. Relevance: This study suggests ways of identifying the source of functional deficiency in the hand. (C) 2000 Elsevier Science Ltd.