Dorsal interossei muscles of the hand
The dorsal interossei muscles are short bipennate intrinsic muscles of the hand. They are found on the dorsal aspect of the hand occupying the space between the metacarpal bones, along with the palmar interossei muscles.
The dorsal interossei muscles consist of four short muscles that attach to the adjacent sides of metacarpals 1-4. Their function is to abduct the digits 2-4, as well as to assist in flexion of these fingers at the metacarpophalangeal (MCP) joints and in extension at the interphalangeal (IP) joints.
So, if you’ve ever wondered how Spock from Star Trek performs his famous greeting with fingers 4-5 medially abducted and fingers 2-3 laterally abducted, now you know the answer - with dorsal interossei.
This article will discuss the anatomy and function of the dorsal interossei muscles.
|Origins||Adjacent sides of metacarpal bones 1-5|
|Insertions||1 & 2: Radial bases of proximal
expansions of digits 2 & 3
3 & 4: Ulnar bases of proximal
expansions of digits 3 and 4
|Function||Metacarpophalangeal joints 2-4: Finger abduction, finger flexion;
Interphalangeal joints 2-4: Finger extension
|Innervation||Deep branch of ulnar nerve (C8-Th1)|
|Blood supply||1: First dorsal metacarpal artery (radial artery)
2, 3 & 4: Second, third, and fourth dorsal metacarpal arteries (dorsal carpal anastomosis)
Origin and insertion
Dorsal interossei are bipennate (feather-like) muscles found in the dorsal compartment of the hand. The prefix bi- means that they arise by two heads which converge to attach onto a central tendon, which gives them a shape of a feather. The dorsal interossei consist of four muscles numbered 1–4 from the lateral to the medial side.
- 1st dorsal interosseous muscle: this muscle is the largest and strongest of the dorsal interossei and is sometimes referred to as abductor indicis. It arises from the adjacent surfaces of the 1st and 2nd metacarpal bones. The muscle fibers converge distally into a tendon which inserts on the radial side of the base of the 2nd proximal phalanx and its dorsal digital expansion.
- 2nd dorsal interosseous muscle: arises from the adjacent surfaces of the 2nd and 3rd metacarpal bones. Like the 1st muscle, the muscle fibers of the 2nd dorsal interosseous converge distally into a tendon which inserts on the radial side of the base of the 3nd proximal phalanx and its dorsal digital expansion.
- 3rd dorsal interosseous muscle: arises from the adjacent surfaces of the 3rd and 4th metacarpal bones. Unlike the 1st and 2nd, the tendon of the 3rd dorsal interosseous inserts on the ulnar side of the base of the 3nd proximal phalanx and its dorsal digital expansion.
- 4th dorsal interosseous muscle: arises from the adjacent surfaces of the 4th and 5th metacarpal bones. The tendon of the 4th dorsal interosseous also inserts on the ulnar side like the 3rd interosseous, attaching on the base of the 4nd proximal phalanx and its dorsal digital expansion.
The dorsal interossei muscles are situated within the dorsal compartment of the hand. They lie deep to the palmar interossei, filling the interosseous space. All four dorsal interossei arise by two heads from each metacarpal bone. The tendons of dorsal interossei cross the posterior side of the deep transverse metacarpal ligament to reach their insertions.
The carpometacarpal joints and the originating fibers of the dorsal interossei create a narrow triangular space between the roots of digits that is traversed by some of the arteries of the hand. The radial artery passes through the first space from the back of the hand into the palm, while the perforating branches arising from the deep palmar arch pass through each of the other spaces.
The first dorsal interosseous can be easily felt in the web between thumb and index finger. Nevertheless, it is also possible to palpate the remaining three between the metacarpal bones and the tendon of the extensor digitorum muscle.
The 1st dorsal interosseous muscle receives vascular supply from the first dorsal metacarpal branch of the radial artery. The 2nd, 3rd, and 4th dorsal interossei receive blood supply from the second, third, and fourth dorsal metacarpal branches of the dorsal carpal anastomosis.
The main function of dorsal interossei is to abduct the fingers 2-4 in a longitudinal axis, moving them away from each other. Put simply, these muscles move the fingers in the following way:
- The dorsal interossei 1-2 pull the digits 2-3 laterally (radial abduction),
- The dorsal interossei 3-4 move the digits 3-4 medially (ulnar abduction).
- The 3rd digit can be abducted both medially and laterally depending on which dorsal interosseous muscle contracts.
The functions of the dorsal interossei are aided by the abductor pollicis brevis, which abducts the thumb, and the abductor digiti minimi, which abducts the little finger. Altogether, these muscles spread the digits. Therefore, the palmar interossei act antagonistically to the palmar interossei muscles, since the latter brings the fingers towards the midline.
In addition to their main function, the dorsal interossei contribute to the flexion in the metacarpophalangeal (MCP) joints and extension in the proximal (PIP) and distal interphalangeal (DIP) joints. Compared to other muscles of the hand acting on these joints, the contribution of dorsal interossei here is rather negligible, but still important in terms of stabilization of these joints.
An analogous muscle group can be found in the foot which is responsible for identical movements at the toes (dorsal interossei of the foot).
Do you want a tried and tested way to distinguish between the actions of the dorsal and palmar interossei muscles? Try using this mnemonic: “PAD DAB” (Use your hand to dab with a pad')
- Palmar interossei - ADduct
- Dorsal interossei - ABduct
Lesions of the deep branch of the ulnar nerve can cause weakness, paralysis and atrophy of the metacarpal and hypothenar muscles innervated by this nerve. This manifests with patients having a weakness to abduct their fingers. In addition, a late manifestation of this lesion is the ulnar claw hand deformity, in which the fingers are extended in the metacarpophalangeal (MCP) joints and flexed in the proximal (PIP) and distal interphalangeal (DIP) joints, giving the appearance of a claw hand.
This is caused by the weakness of the third and fourth lumbricals, in addition to the interossei. Conversely, the index and middle fingers are usually less affected in the ulnar claw because the first and second lumbricals can compensate for this loss up to a certain degree. The reason behind this is that those two muscles are not supplied by the ulnar nerve, but instead the median nerve.
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