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Interosseous muscles are found in the hand and are considered voluntary muscles. They are divided into two groups: the palmar interossei and the dorsal interossei. The palmar interossei consist of three short, unipennate muscles on the palmar surface of the hand, while the dorsal interossei consist of four short muscles that attach to the adjacent sides of metacarpals 1-4. These muscles help control the fingers by abducting and adducting them, as well as assisting in flexion and extension at the metacarpophalangeal and interphalangeal joints.
| Characteristics | Values |
|---|---|
| Location | Dorsal aspect of the hand |
| Muscle type | Voluntary |
| Number of muscles | 4 |
| Function | Abduct digits 2-4, assist in flexion of fingers at the metacarpophalangeal (MCP) joints and in extension at the interphalangeal (IP) joints |
| Innervation | Deep branch of the ulnar nerve |
| Blood supply | Dorsal metacarpal arteries |
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What You'll Learn
- Interossei muscles are attached either proximally or distally on the extensor expansion
- The dorsal interossei muscles are short bipennate intrinsic muscles of the hand
- Palmar interossei are smaller than the dorsal interossei
- Injury to the ulnar nerve can cause weakness or atrophy of the interossei muscles
- Interossei muscles play a key role in the function of the hand: grip and pinch
Interossei muscles are attached either proximally or distally on the extensor expansion
The interossei muscles are intrinsic muscles of the hand, which help to control the fingers. They are considered voluntary muscles. The interossei muscles can be divided into two groups: the palmar interossei and the dorsal interossei.
The palmar interossei are three short, unipennate muscles on the palmar surface of the hand. They occupy the spaces between the metacarpal bones, attaching to the index, ring, and little fingers. The function of the palmar interossei is to adduct the digits towards the 3rd digit (towards the axial line).
The dorsal interossei, on the other hand, are four short muscles that attach to the adjacent sides of metacarpals 1-4. They are bipennate muscles found in the dorsal compartment of the hand. The function of the dorsal interossei is to abduct the digits away from the 3rd digit (away from the axial line).
With some individual variations, the interossei muscles are attached either proximally or distally on the extensor expansion. The first dorsal interosseous is the most consistent, inserting entirely into the base of its proximal phalanx and the extensor hood. The second, third, and fourth dorsal interossei have insertions proximally on the base of the metacarpal and hood, and distally on the lateral bands and central tendon of the extensor mechanism. The abductor digiti minimi, or the fifth dorsal interosseus, has only a proximal insertion. In contrast, the palmar interossei have only distal insertions. Thus, the interossei can be categorised into proximal and distal groups. The proximal interossei primarily affect the metacarpophalangeal (MP) joints, while the distal interossei mainly influence the interphalangeal (IP) joints.
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The dorsal interossei muscles are short bipennate intrinsic muscles of the hand
The innervation of all dorsal interossei is carried by the deep branch of the ulnar nerve, derived from nerve roots C8 and T1. The skin that overlies the muscles is supplied by the roots C6-C8. The first dorsal interosseous muscle receives vascular supply from the first dorsal metacarpal branch of the radial artery. The second, third, and fourth dorsal interossei receive blood supply from the second, third, and fourth dorsal metacarpal branches of the dorsal carpal anastomosis.
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 fibres of the dorsal interossei create a narrow triangular space between the roots of the digits that is traversed by some of the arteries of the hand.
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. Together, these muscles spread the digits. Therefore, the palmar interossei act antagonistically to the palmar interossei muscles, as the latter brings the fingers towards the midline. In addition to their main function, the dorsal interossei contribute to the flexion in the 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 the dorsal interossei is rather negligible, but they still play an important role in the stabilisation of these joints.
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Palmar interossei are smaller than the dorsal interossei
The interosseous muscles of the hand are muscles found near the metacarpal bones that help to control the fingers. They are considered voluntary muscles. The palmar interossei are smaller than the dorsal interossei and are situated on the palmar surface of the hand in between the metacarpal bones. The dorsal interossei muscles, on the other hand, 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.
The palmar interossei consist of four muscles that attach to the 1st, 2nd, 4th, and 5th fingers, with the 3rd finger being an exception. The first palmar interosseous, also known as the pollical palmar interosseous, originates at the medial palmar surface of the first metacarpal and is often considered rudimentary. The second palmar interosseous originates at the medial surface of the base of the second metacarpal. The third and fourth palmar interossei originate at the lateral aspect of the fourth and fifth metacarpals.
The palmar interossei are strong adductors of the fingers, assisting in flexion of the metacarpophalangeal joints and extension of the interphalangeal joints. They are also known as volar and are unipennate muscles, in contrast to the bipennate dorsal interossei. 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 and assist in flexion and extension of these fingers at the metacarpophalangeal (MCP) and interphalangeal (IP) joints, respectively.
The dorsal interossei are predominantly in the proximal group, which makes them more effective at the MP joints than the palmar interossei. This means that abduction is stronger than adduction at the MP joints. The functions of the dorsal interossei are aided by the abductor pollicis brevis and the abductor digiti minimi, which abduct the thumb and little finger, respectively. The palmar interossei, on the other hand, act antagonistically to the dorsal interossei muscles, bringing the fingers towards the midline or the axial line.
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Injury to the ulnar nerve can cause weakness or atrophy of the interossei muscles
The interosseous muscles are found near the metacarpal bones and help control the fingers. These muscles are divided into two groups: the palmar interossei and the dorsal interossei. The palmar interossei adduct the digits towards the third digit (towards the axial line) and are unipennate. The dorsal interossei, on the other hand, abduct the digits away from the third digit (away from the axial line) and are bipennate.
The ulnar nerve is one of the five peripheral nerves that the brachial plexus branches into. It is susceptible to compression injuries, especially at the elbow and the wrist. This type of injury is called ulnar nerve entrapment and it can cause muscle weakness or atrophy, especially in the hypothenar, lumbrical, and interosseous muscles. Ulnar nerve entrapment at the elbow is known as Cubital Tunnel Syndrome, which is the second most common entrapment neuropathy. Symptoms of ulnar nerve entrapment include tingling in the fourth and fifth fingers, weak grip strength, pain and sensitivity on the ulnar side of the forearm, wrist, and hand, muscle atrophy, and clawing of the fourth and fifth fingers.
Injury to the ulnar nerve can, therefore, cause weakness or atrophy of the interossei muscles. 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 can manifest as a patient's weakness in abducting their fingers. A late manifestation of this lesion is the ulnar claw hand deformity, where the fingers extend in the metacarpophalangeal joints and flex in the proximal and distal interphalangeal joints, resulting in a claw-like appearance.
The extent of nerve injuries can vary from mild neurapraxia, where the nerve experiences mild ischemia caused by compression, to severe neurotmesis, where the nerve suffers full-thickness damage and may not fully recover. Most nerve injuries observed in clinical practice involve neurapraxia, resulting from entrapment along the nerve's anatomical course. A detailed history and physical examination are often sufficient to identify the injury, but advanced imaging techniques such as MRI and ultrasonography may be required in more severe cases.
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Interossei muscles play a key role in the function of the hand: grip and pinch
The interosseous muscles of the hand are a group of muscles found near the metacarpal bones that help control the fingers. They are considered voluntary muscles. The interossei muscles play a key role in the function of the hand: grip and pinch.
The interossei muscles can be divided into two groups: the dorsal interossei and the palmar interossei. 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. The first dorsal interosseous muscle has its origin on the adjacent surfaces of the first and second metacarpal bones and inserts into the lateral base of the second metacarpal. The second, third, and fourth dorsal interossei have insertions proximally on the base of the metacarpal and distally on the lateral bands and central tendon of the extensor mechanism.
The palmar interossei, in contrast, have only distal insertions. There are three palmar interossei, and they are smaller than the dorsal interossei. They are attached to the index, ring, and little fingers. The first palmar interossei, also known as the pollical palmar interosseous, originates at the medial palmar surface of the first metacarpal. The second palmar interosseous originates at the medial surface of the base of the second metacarpal. The third and fourth palmar interossei originate at the lateral aspect of the fourth and fifth metacarpals. The palmar interossei are strong adductors of the fingers and assist in flexion of the metacarpophalangeal joints and extension of the interphalangei.
The dorsal and palmar interossei work together to control the fingers. The dorsal interossei abduct the fingers, while the palmar interossei adduct them. This means that the dorsal interossei move the fingers away from the axial line (an imaginary line down the middle of the 3rd digit), while the palmar interossei move the fingers towards this line. This action of the interossei muscles helps to produce the grip and pinch functions of the hand.
Injuries to the interossei muscles can have debilitating effects on hand function. For example, lesions of the deep branch of the ulnar nerve can cause weakness, paralysis, and atrophy of the interossei muscles, leading to a condition known as the ulnar claw hand deformity. This condition is characterised by the extension of the fingers in the MCP joints and flexion in the PIP and DIP joints, resulting in a claw-like appearance.
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Frequently asked questions
Interosseous muscles are muscles found near the metacarpal bones that help control the fingers.
There are two types of interosseous muscles: dorsal interosseous muscles and palmar interosseous muscles.
The dorsal interosseous muscles are a group of four paired intrinsic muscles of the hand located between the metacarpals. They are the major abductors of the second, third, and fourth digits at the metacarpophalangeal joints.
The palmar interosseous muscles are three short, unipennate muscles on the palmar surface of the hand. They are smaller than the dorsal interosseous muscles. The palmar interosseous muscles act antagonistically to the dorsal interosseous muscles, as they bring the fingers towards the midline.
The interosseous muscles play a key role in hand functions such as grip and pinch. They also contribute to flexion and extension at the interphalangeal joints.
