Role of intertendinous connections in distribution of force in the human extensor digitorum muscle

Abstract

The human extensor digitorum (ED) muscle gives rise distally to multiple tendons that insert onto and extend digits 2-5. It has been shown previously that the spike-triggered average forces of motor units in ED are broadly distributed across many tendons. Such force dispersion may result from linkages between the distal tendons of ED and may limit the ability to move the fingers independently. The purpose of this study, therefore, was to determine the extent to which the connections between tendons of ED distribute force across the fingers. Stimulation of ED muscle fibers was performed at 107 different sites in four subjects. The isometric force exerted on digits 2-5 resulting from the stimulation was measured separately. Stimulus-triggered averaging of each of the four force channels yielded the force contribution to each of the digits due to the stimulation at each site. A selectivity index from 0 (a site that distributes force equally across the fingers) to 1.0 (a site that produces force on a single finger) was computed to describe the distribution of force across the four fingers. The selectivity index resulting from electrical stimulation of ED averaged 0.70 +/- 0.21. These selectivity index values were significantly greater (P < 0.001) than those obtained for single motor units using spike-triggered averaging. These findings suggest that linkages between the distal tendons of ED probably play only a minor role in distributing force across the fingers and, therefore, other factors must be primarily responsible for the inability to move the fingers independently.

Analysis of Hand and Wrist Postural Synergies in Tolerance Grasping of Various Objects

“…Secondly, for the functional organization of multitendoned finger muscles, the extrinsic finger muscles (flexor digitorum superficialis, FDP, and EDC) have multiple tendons mapping to various joints of the hand, which lead to the mapping relation between joints and muscles is not a simple corresponding relation like one to one. The coupling movements of various joints will be occurred when each extrinsic finger muscles (flexor digitorum superficialis, FDP, and EDC) have a contraction [37–38]. Finally, for the commands coming from central nervous system (CNS), the influence to joint movement correlations can be divided into two parts.…”

An integrative approach to the biomechanical function and neuromuscular control of the fingers

“…does not yet address important issues such as neural and anatomical coupling among digits (Leijnse et al, 1993;Zatsiorsky et al, 1998;Latash et al, 2001;Li et al, 2001a;Keen and Fuglevand, 2003;Keen and Fuglevand, 2004a;Keen and Fuglevand, 2004b;Maas et al, 2004) or free finger motion (Cole and Abbs, 1986;Dennerlein et al, 1998b;Santello et al, 1998;Dennerlein et al, 1999;Sancho-Bru et al, 2001).…”

Extrinsic Finger and Thumb Muscles Command a Virtual Hand to Allow Individual Finger and Grasp Control

“…Extensor digitorum communis (EDC), flexor digitorum profundus (FDP), and flexor digitorum superficialis (FDS) are extrinsic muscles that have individual finger and tendon compartments and have been shown to be physically and functionally distinct [26–31]. Regardless, these individual digit motions are the coordinated effort of multiple muscles and usually result in both force being exerted by adjacent digits (force enslavement) [32, 33] and activity emitted from adjacent muscle compartments (spillover recruitment) [30, 34–36].…”