Abductor digiti minimi of hand

At a glance

English

Abductor digiti minimi of hand

Latin (TA2)

Abductor digiti minimi manus

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the abductor digiti minimi of hand

Three short muscles act on the little finger from within the hand, and together with fat and skin they form the fleshy hypothenar eminence on the ulnar side of the palm. Of these, abductor digiti minimi lies most superficial and furthest medial, running along the outer border of the hand; flexor digiti minimi brevis lies beside it and opponens digiti minimi lies deeper.

The muscle begins at the wrist on the pisiform bone, the small pea-shaped carpal bone at the base of the hypothenar eminence, and on the tendon of flexor carpi ulnaris, which ends on the pisiform, with fibres from the pisohamate ligament. Its spindle-shaped belly runs down the edge of the palm to a tendon that attaches to the ulnar side of the base of the proximal phalanx of the little finger. Part of the tendon continues into the extensor expansion on the back of the finger, and a sesamoid bone may be found at the joint. Accessory slips from the forearm fascia, the palmaris longus tendon or the flexor retinaculum are common, making it the most variable of the hypothenar muscles.

Its chief action is to swing the little finger out, away from its neighbour, at the knuckle (metacarpophalangeal) joint. Because it joins the extensor expansion, it also behaves like a dorsal interosseous muscle, helping to flex the knuckle joint while straightening the joints of the finger. It is especially useful when the hand is spread wide to grasp a large object, such as a ball. Like the other hypothenar muscles, its nerve is the ulnar nerve's deep branch, from the eighth cervical and first thoracic segments, and receives blood from the ulnar artery and its deep palmar branch.

Weakness or wasting of this muscle, with flattening of the hypothenar eminence, is a sign of ulnar nerve damage at the wrist or elbow. In the same injury the little finger often drifts away from the ring finger and cannot be brought back, known as Wartenberg sign; this comes from the pull of the extensor of the little finger once the palmar interosseous that adducts it is weak.

Attachments, action and supply

Origin

Pisiform bone, the tendon of flexor carpi ulnaris and the pisohamate ligament.

Insertion

Ulnar side of the base of the proximal phalanx of the little finger, and the extensor expansion.

Action

Abducts the fifth digit at its metacarpophalangeal joint; helps flex that joint and extend the interphalangeal joints.

Nerve supply

Ulnar nerve, deep branch (C8, T1).

Blood supply

Ulnar artery and its deep palmar branch.