Anatomic Basis for Individuated Surface EMG and Homogeneous Electrostimulation With Neuroprostheses of the Extensor Digitorum Communis

Abstract

The extensor digitorum communis (ED) is generally regarded as a fairly undiversified muscle that gives extensor tendons to all fingers. Some fine wire electromyographic (EMG) investigations have been carried out to study individuation of the muscle parts to the different fingers. However, individuated surface EMG of the ED has not been investigated. This study analyses the anatomy of the ED muscle parts to the different fingers in detail and proposes optimal locations for surface or indwelling electrodes for individuated EMG and for electrostimulation with neuroprostheses. The dissections show that the ED arises from extensive origin tendons (OT), which originate at the lateral epicondyle and reach far in the forearm. The ED OT is V-shaped with shorter central tendon fibers but with a long radial and an even longer ulnar slip. The ED parts to the individual fingers consistently arise from distinct OT locations: the ED3 (medius) arises proximally, the ED2 (index) from the radial slip distal to ED3, the ED4 (ring finger) from the ulnar slip distal to ED3, and the ED5 (to ring/little finger) from the ulnar slip distal to ED4. This lengthwise widely spaced arrangement of ED parts compensates to some degree for the narrow ED width and suggests that ED parts should be individually assessable by indwelling and even by surface EMG electrodes, albeit in the latter case with variable mutual cross-talk. Conversely, the anatomic spacing of ED parts warrants that electromyographic stimulation with neuroprostheses by a single implanted electrode cannot likely homogeneously activate all ED parts.

Activation of individual extrinsic thumb muscles and compartments of extrinsic finger muscles

“…Three of the extrinsic finger muscles have a compartment and tendon for each of the four fingers. Leijnse and colleagues have identified these individual muscle compartments and potential locations for surface sensors to measure their electromyographic (EMG) activity (Leijnse 1997a;Leijnse et al 1997Leijnse et al , 2008aLeijnse et al , 2008b. However, the action of each compartment can have an effect on more than one digit, and the relationship is only partially understood.…”

Understanding of hand muscles involvement: towards a linkage between biomechanical modeling and motor control theories

“…Second, the different levels of co-contraction observed for each finger in FCR does not agree with the unique compartment of this muscle in contrast with the separated EDC compartments (Leijnse, Carter, Gupa, & McCabe, 2008). One explanation lies probably in the specific tendon tensioning performed by the surgeon for the different fingers.…”

Index finger prosthesis control method according to human intention

“…It is well-known that the FDS muscle is activated during the flexion motion of the index finger and the EI muscle is activated during the extension motion of the index finger [17,18] , respectively. Also, the measured EMG signal can be divided into an initial burst part and a long plateau according as a muscle generates a force with changing the length of the muscle.…”