Dominic Stone
The palmar interossei muscles are a group of four muscles that contribute to palmar flexion, which is the movement of the hand and wrist down towards the palm. These muscles are located on the palmar surface of the hand and are smaller than the dorsal interossei muscles. They adduct the thumb, index, ring, and little fingers, assisting in flexion at the metacarpophalangeal joints and extension at the interphalangeal joints. The palmaris longus muscle also plays a role in palmar flexion, aiding in wrist flexion and tensioning the palmar aponeurosis. This muscle is located in the anterior forearm and works with the flexor carpi ulnaris and flexor carpi radialis muscles to enable palmar flexion.
| Characteristics | Values |
|---|---|
| Type | Three short, unipennate muscles |
| Location | Palmar surface of the hand |
| Attachments | Index, ring, and little fingers |
| Adduction | Adduct digits toward axial line |
| Flexion | Assist lumbricals in flexing metacarpophalangeal joints |
| Extension | Extend interphalangeal joints |
| Innervation | Deep branch of ulnar nerve (C8 and T1) |
| Arterial Supply | Palmar metacarpal arteries |
| Function | Plays an important role in the anatomy of the grip |
| Additional Actions | Wrist flexion and tensioning the palmar aponeurosis |
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What You'll Learn
- Palmar interossei muscles adduct fingers and assist in flexing the metacarpophalangeal joints
- Palmaris longus flexes the hand on the wrist
- Flexor carpi ulnaris and flexor carpi radialis are prime movers in palmar flexion
- Palmaris longus stabilises the elbow joint when extended
- Palmar interossei muscles are smaller than the dorsal interossei
Palmar interossei muscles adduct fingers and assist in flexing the metacarpophalangeal joints
The palmar interossei muscles are three short, unipennate muscles on the palmar surface of the hand. They occupy the spaces between the metacarpal bones and are attached to the index, ring, and little fingers. They are smaller than the dorsal interossei of the hand.
The palmar interossei muscles are strong adductors of the fingers. They adduct the fingers towards the centre of the third digit or middle finger. Specifically, the first palmar interosseous pulls the index finger medially, while the second and third pull the ring and little fingers laterally.
These muscles also assist in flexing the metacarpophalangeal joints and extending the interphalangeal joints. The lumbricals are the major contributors to flexion at the metacarpophalangeal joints, but the interossei also play a role in these movements.
The palmar interossei receive innervation from the deep palmar branch of the ulnar nerve. Injury to the ulnar nerve can manifest as weakness or atrophy of the interossei muscles. Ulnar nerve entrapment is the second most prevalent compression neuropathy in patients. Depending on which nerve fibres are compromised, patients may experience weakness in adduction of the fingers.
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Palmaris longus flexes the hand on the wrist
The palmaris longus is a slender, elongated, spindle-shaped muscle that lies on the medial side of the flexor carpi radialis. It is involved in wrist flexion and plays a role in the anatomy of the grip. The muscle is located centrally in the anterior forearm and works alongside the flexor carpi ulnaris and flexor carpi radialis muscles to enable a balanced flexion of the hand on the wrist.
Palmaris longus is also involved in tightening and tensing the palmar aponeurosis, a structure that covers the palm of the hand. This action helps to stabilise the elbow joint when it is fully extended. Additionally, the tightening of the palmar aponeurosis contributes to maintaining a secure grip while holding objects.
The muscle is innervated by the median nerve and arises from the medial epicondyle of the humerus via the common flexor tendon. It also originates from adjacent structures like the intermuscular septa and the antebrachial fascia. The tendon of the palmaris longus is visible and palpable when the wrist is flexed and the pads of the fourth finger and thumb are touched.
The palmaris longus tendon is of significant interest to surgeons due to its utility in tendon grafts for the wrist and upper limb tendon repair. Its absence does not affect grip strength but does result in decreased pinch strength in the fourth and fifth fingers. The muscle is also associated with pathological processes in Median and Ulnar nerve neuropathies.
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Flexor carpi ulnaris and flexor carpi radialis are prime movers in palmar flexion
The flexor carpi ulnaris and flexor carpi radialis are indeed prime movers in palmar flexion, which is the movement of bending the wrist towards the palm. These muscles work together with the palmaris longus to produce flexion of the hand at the wrist joint.
The flexor carpi ulnaris is a fusiform muscle located in the anterior compartment of the forearm. It is the most medial of the superficial flexors and has two heads: a humeral head and an ulnar head. The humeral head originates from the medial epicondyle of the humerus, while the ulnar head originates from the olecranon and proximal part of the posterior border of the ulna. The muscle fibres converge on a long tendon in the distal part of the forearm, which inserts onto the pisiform and hamate carpal bones, as well as the base of the fifth metacarpal bone. This muscle not only flexes the hand but also moves it sideways and is involved in adduction of the hand at the wrist, also known as ulnar deviation or ulnar flexion.
The flexor carpi radialis is also located in the anterior forearm and is one of the long forearm flexors. It is the most lateral of the tendons in the distal forearm, sitting lateral to the flexor carpi ulnaris tendon. Together, these muscles produce a balanced flexion of the hand on the wrist.
The palmaris longus is another muscle that aids in wrist flexion and tensioning the palmar aponeurosis. It stabilises the elbow joint when fully extended and tightens the palmar aponeurosis, resulting in a weak flexion of the 2nd to 5th metacarpophalangeal joints.
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Palmaris longus stabilises the elbow joint when extended
The palmaris longus muscle is located centrally in the anterior forearm. It is a superficial forearm flexor that mainly participates in wrist flexion. The muscle flexes the hand on the wrist, working alongside the flexor carpi ulnaris and flexor carpi radialis muscles to perform a balanced flexion of the hand on the wrist. The palmaris longus also has a role in tensioning the palmar aponeurosis, which is a fascial sheath that tightens during the contraction of the palmaris longus muscle. This tightening results in a weak flexion of the 2nd to 5th metacarpophalangeal joints as the aponeurosis is pulled towards the wrist.
The palmaris longus muscle also has a stabilising function at the elbow joint. When the elbow is fully extended, the palmaris longus, along with the other forearm muscles that attach to the humerus and cross the elbow joint, helps to stabilise this position. This stabilisation is achieved through the fibres that attach to the palmar aponeurosis, which tightens and provides support to the elbow joint when fully extended.
The palmaris longus muscle has a relatively short inferior course, with a long tendon that originates midway down the forearm. This tendon enters the palmar surface of the hand by passing externally to the flexor retinaculum, also known as the transverse carpal ligament. The flexor retinaculum forms the "carpal tunnel," a structure supported by the carpal bones and through which the flexor tendons, median nerve, and several arteries and veins travel. The palmaris longus muscle shares a tendinous hub with the five long forearm flexors, including the flexor carpi ulnaris and flexor carpi radialis.
The absence of the palmaris longus muscle does not seem to significantly affect grip strength. However, the presence or absence of this muscle can vary among individuals, with certain ethnic variations and a higher prevalence in men than in women. The palmaris longus is considered a phylogenetically retrogressive muscle, characterised by a short belly and a long tendon. Clinical tests have been developed to detect the presence of the palmaris longus muscle by positioning the wrist and hand to tension the muscle, making its tendon visible and palpable.
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Palmar interossei muscles are smaller than the dorsal interossei
The palmar interossei muscles are smaller than the dorsal interossei. They are three short, unipennate muscles on the palmar surface of the hand and, along with the dorsal interossei muscles, occupy the spaces between the metacarpal bones. These are attached to the index, ring, and little fingers. The palmar interossei muscles are strong adductors of the fingers and assist in flexion of the metacarpophalangeal joints and extension of the interphalangeal joints. The lumbricals are the major contributors to flexion at the metacarpophalangeal joints, as well as extension at the distal interphalangeal and proximal interphalangeal joints. However, the interossei also play a minor role in these movements.
The first palmar interossei, also known as the pollical palmar interosseous, originate at the medial palmar surface of the first metacarpal. It 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 muscles receive arterial blood supply from the palmar metacarpal arteries and drain into the palmar metacarpal veins. The palmar metacarpal arteries derive from the deep palmar arch, which is comprised of the terminal portion of the radial artery and the deep branch of the ulnar artery. The palmar interossei receive innervation from the deep branch of the ulnar nerve. An injury to the ulnar nerve can manifest as weakness or atrophy of the interossei muscles. Ulnar nerve entrapment is the second most prevalent compression neuropathy in patients. Depending on which nerve fibres are compromised, patients may experience weakness in adduction of the fingers.
The palmar interossei muscles play a critical role in grip strength and precision tasks, making them key considerations in hand rehabilitation and post-surgical recovery. Detailed knowledge of the location and innervation of these muscles supports safer surgical navigation during procedures involving the ulnar side of the hand, reducing the risk of iatrogenic injury.
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Frequently asked questions
Palmar flexion, or the movement of the hand and wrist downwards towards the palmar side, is performed by the palmar interossei muscles. These are three short, unipennate muscles on the palmar surface of the hand, attached to the index, ring, and little fingers.
The palmar interossei muscles are strong adductors of the fingers and assist in flexion of the metacarpophalangeal joints and extension of the interphalangeal joints.
Yes, the palmaris longus muscle, which is located centrally in the anterior forearm, also contributes to palmar flexion. It aids the flexor carpi ulnaris and flexor carpi radialis muscles in performing a balanced flexion of the hand on the wrist.
