The hypothenar muscles are the four short muscles of the medial (ulnar) palmar compartment of the hand. From superficial to deep, the hypothenar muscles are: palmaris brevis, abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi muscles.
The hypothenar muscles are intrinsic muscles of the hand located within the medial side of the palm. They span between the medial aspect of the carpus to the carpal and metacarpal bones of the little finger. These muscles form a noticeable fleshy prominence on the medial side of the palm called the hypothenar eminence.
All of the hypothenar muscles, except for palmaris brevis, are innervated by the deep branch of ulnar nerve (C8, T1). However, the palmaris brevis muscle is supplied by the superficial branch of ulnar nerve (C8, T1). The blood supply for the hypothenar eminence comes mainly from the ulnar artery via the superficial palmar arch. The function of the hypothenar muscles is to contribute to the variety of movements of the little finger; flexion, abduction, lateral rotation, and opposition.
This article will introduce you to the anatomy and function of the hypothenar muscles.
|Definition and function||Intrinsic muscles of the hand that comprise the hypothenar eminence of the palm and produce movements on the joints of the little finger.|
|Muscles||Abductor digiti minimi, flexor digiti minimi, opponens digiti minimi, palmaris brevis|
|Innervation||Ulnar nerve (C8, T1)|
|Blood supply||Ulnar artery via the superficial palmar arch|
|Function||Flexion, abduction, lateral rotation, and opposition of the little finger|
- Abductor digiti minimi muscle
- Flexor digiti minimi brevis muscle
- Opponens digiti minimi muscle
- Palmaris brevis muscle
- Clinical aspects
Abductor digiti minimi muscle
The abductor digiti minimi muscle of the hand is a short muscle that originates from the palmar surface of the pisiform bone and the dorsal aponeurosis. It courses along the ulnar side of the metacarpal bone 5 and inserts to the ulnar aspect of the base of the proximal phalanx of the 5th digit, as well as to the extensor expansion of the 5th digit.
The abductor digiti minimi muscle is innervated by the deep branch of ulnar nerve (C8, T1). The function of the abductor digiti minimi muscle is to flex and abduct the fifth digit at its metacarpophalangeal joint, as well as to flex it at its interphalangeal joint.
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Flexor digiti minimi brevis muscle
The flexor digiti minimi brevis muscle of the hand originates from the hook of hamate bone and medial aspect of flexor retinaculum. It crosses the fifth metacarpophalangeal joint and, together with abductor digiti minimi, it inserts to the medial side of the base of proximal phalanx of the little finger.
The muscle shares the same innervation as the abductor digiti minimi, i.e. the deep branch of ulnar nerve (C8, T1). The function of the flexor digiti minimi muscle is to flex the fifth digit on the metacarpophalangeal joint, as well as to participate in the lateral rotation and opposition of the little finger.
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Flexor digiti minimi brevis anatomy is waiting for you here.
Opponens digiti minimi muscle
The opponens digiti minimi muscle lies deep to abductor and flexor digiti minimi muscles. It originates from the hook of hamate bone and flexor retinaculum. After a short oblique course, the muscle inserts to the ulnar side of the metacarpal bone 5.
Just like the abductor and flexor digiti minimi, the opponens digiti minimi muscle is innervated by the deep branch of ulnar nerve. Its function is to flex the fifth digit on the metacarpophalangeal joint 5, as well as to laterally rotate and oppose the fifth digit.
Learn more about the opponens digiti minimi muscle here!
Palmaris brevis muscle
The palmaris brevis muscle is found in the subcutaneous tissue of the hypothenar region. It originates from the palmar aponeurosis and flexor retinaculum, passes nearly horizontally and inserts to the dermis of the hypothenar skin.
Unlike the rest of the hypothenar muscles, the palmaris brevis is innervated by the superficial branch of the ulnar nerve (C8, T1). The function of the palmaris brevis muscle is to tighten the palmar aponeurosis and to contribute to the strength of the grip. Since this muscle doesn't primarily act on the fifth digit, it is sometimes considered separate to this muscle group.
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The Guyon’s canal is a typical place of entrapment of the ulnar nerve leading to a clinical picture referred to as the Guyon's canal syndrome. The most common causes are:
- chronic compression (e.g. resting the hand on the bicycle handlebar)
- rather rarely, tumors
The affected patients complain about pain and disturbed sensation at the ulnar side of the palm. In advanced stages, paralysis and atrophy of the hypothenar and metacarpal muscles occur.
In order not to mistake the Guyon’s canal syndrome with the more common carpal tunnel syndrome the following examinations should be performed:
- Tapping lightly on both the Guyon's canal and carpal tunnel. If there is local paraesthesia one should suspect an underlying compression. This test, referred to as Hoffmann-Tinel sign, can be performed at the site of any suspected peripheral nerve compression.
- Asking the patient to grasp a sheet of paper between thumb and index finger. If there is a weakness of the adductor pollicis muscle, the patient will try to compensate it by using the flexor pollicis longus muscle which is innervated by a branch of the median nerve (Froment's sign).