Image by/from modified by Uwe Gille
In human anatomy, the abductor digiti minimi (abductor minimi digiti, abductor digiti quinti, ADM) is a skeletal muscle positioned on the ulnar border of the palm of the hand. It forms the ulnar border of the palm and its spindle-like shape defines the hypothenar eminence of the palm together with the skin, connective tissue, and fat surrounding it. Its main function is to pull the little finger far from the other fingers (i.e. abduction).
The abductor digiti minimi arises from the pisiform bone, the pisohamate ligament, and the flexor retinaculum.
Its distal tendon ends in three slips that are placed into the ulnopalmar margin of the proximal phalanx, the palmar plate of the metacarpophalangeal joint, and the sesamoid bone when present. Some fibers place into the finger’s dorsal aponeurosis, which is why the muscle acts similar to a dorsal interosseus muscle.
Furthermore, the ulnar-most part of the tendon inserts into the little finger’s digital cable, and the muscle therefore forms part of a structure that bends the metacarpophalangeal joint and extends the interphalangeal joints.
It is innervated by the deep branch of the ulnar nerve (C8-T1).
The abductor digit minimi develops at an early stage from an ulnar muscle primordium of the superficial layer of the original undifferentiated mesenchyme of the hand, together with the flexor digitorum superficialis (medial primordia) and the abductor pollicis brevis (radial). In contrast, the remaining hypothenar muscles are stemmed from the deep layer at a later phase.
The abductor digiti minimi is the most variable hypothenar muscle, and may be joined by accessory slips from the tendon of the flexor carpi ulnaris, the flexor retinaculum, the fascia of the distal lower arm, or the tendon of the palmaris longus. Occasionally, the muscle is partly placed onto the 5th metacarpal bone.
In case of polydactyly it might place to the 6th finger instead, if there is one.
It is an abductor of the little finger at the metacarpophalangeal joint.
It is likewise possible that the muscle adds to extension of the middle phalanx of the little finger through its connection to finger’s extensor mechanism.
It plays an essential function when the hand is grasping large things with outspread fingers.
The name is derived from the Latin -ab “away from”; ducere “to draw”; digitus, “digit”; and minimum, smallest; or quintus, “fifth”, meaning “abductor of the smallest or fifth finger”.
Transverse section across the wrist and digits.
Abductor digiti minimi muscle
Muscles of hand. Cross section.