Morphology and functional anatomy of the first dorsal interosseous muscle of the hand.

The aim of this study, based upon anatomical and electrophysiological evaluation, was to identify the relationship between the morphology and physiology of the first dorsal interosseous muscle of the hand, which should be distinguished from the other dorsal interosseous muscles of the hand. Its morphology, distal attachments and physiology have been subject of numerous studies yielding conflicting results. The study reported herein was made on the basis of anatomical and electrophysiological investigation. Most of the dissections (20/34) were made on fresh specimens. Results of this study confirm the existence of the deep and superficial heads of the 1st dorsal interosseous muscle. The muscle is attached distally to the palmar plate of the metacarpophalangeal joint, the lateral tubercle of the base of the proximal phalanx of the index and the interosseous hood. Conversely, the muscle did not show any attachment to the oblique radial wing of the extensor apparatus in our dissections. The deep head of the muscle causes mainly flexion pinch between thumb and index superficial head abduction. Within the complex physiology of the various types of apposition of thumb and index, the dorsal interosseous muscle acts as a stabilizer. The results of electrophysiological study confirmed most of the interpretations deduced from morphological investigation.