Dorsal interossei muscles (hand)
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The interossei muscles form part of the intrinsic muscles of the hand, and as a group consisting of four palmar (1st is often rudimentary) and four dorsal muscles. Collectively, the interossei contribute to abduction and adduction of the fingers and also contribute to flexion of the metacarpophalangeal joints (MCPJ) and extension of the interphalangeal joints (IPJ) through their insertion onto the extensor hood. The reference axis through which abduction and adduction occur is the long axis of the 3rd phalanx (middle finger).
- origin: contiguous (adjacent) sides of the five metacarpal bones
insertion: extensor hood of their related digit and the base of the proximal phalanx
- 1st and largest: 2nd digit dorsal digital expansion and radial side of 2nd proximal phalanx
- 2nd: 3rd digit dorsal digital expansion and radial side of 3rd proximal phalanx
- 3rd: 3rd digit dorsal digital expansion and ulnar side of 3rd proximal phalanx
- 4th: 4th digit dorsal digital expansion and ulnar side of 4th proximal phalanx
- innervation: deep branch of the ulnar nerve (C8, T1)
- primary: abduction of 2nd, 3rd, and 4th fingers at the MCPJ joints; the 3rd finger can abduct both medially and laterally
- secondary: contributes to the flexion of MCPJ and extension of the proximal interphalangeal joint and distal interphalangeal joint
The dorsal intrinsic muscles of the hand are bipennate and are the most dorsally situated of all intrinsic muscles of the hand. They are associated with abduction of the 2nd, 3rd, and 4th fingers, and their tendons run dorsally to the deep transverse metacarpal ligament.
The dorsal interossei are supplied mainly by the dorsal and palmar metacarpal arteries, radial artery, princeps pollicis artery, radialis indicis artery and three perforating branches from the deep palmar arch.
The mnemonic “PAD” and “DAB” can be used to help remember the different functions of the two muscle groups.
- Palmar = ADduction
- Dorsal = ABduction
The first dorsal interosseous muscle can be tested by placing the patient's palm flat on a table and asking the patient to abduct his/her index finger against the examiner's resistance. The muscle belly can be both seen and felt and is a reliable test for the ulnar nerve.