Abductor Digiti Minimi (Hand)

General information

The abductor digiti minimi is a muscle whose primary function is to move the little finger laterally away (abduct) from the rest of the fingers.

It is located on the ulnar side of the palm of the hand, forming the ulnar border and marking the hypothenar eminence of the palm with the skin, fat, and connective tissue which covers it.

Literal meaning

Abductor of the smallest finger.

Interesting information

The abductor digiti minimi develops from the ulnar muscle primordial of the superficial layer of the original undifferentiated mesenchyme in the hand. It develops along with the abductor pollicis brevis and the flexor digitorum superficialis. These muscles develop at an early stage while the other hypothenar muscles develop at a later stage from the deep layer of the mesenchyme.

There can be some variance in the structure of the abductor digiti minimi, with some accessory fascicles arising from the radius, ulna, and the antebrachial fascia.

There is a rare condition known as polydactyly which causes the body to develop extra or supernumerary digits or limbs. In subjects with polydactyly, the abductor digiti minimi has been observed inserting into the sixth finger instead of the fifth.

Origin

This muscle originates from the pisohamate ligament, pisiform bone, and flexor retinaculum.

Insertion

The abductor digiti minimi inserts at the base of the proximal phalanx of the fifth digit on the medial or ulnar side.

Function

The function of the abductor digiti minimi is to abduct the fifth or little finger.

Nerve supply

The deep branch of the ulnar nerve.

Blood supply

Ulnar artery.

Relevant research

During the dissection of 62 adult post-mortem forearms, it was discovered that there existed two instances of anomalous fascicles in abductor digiti minimi.

The study goes on to make some fascinating parallels between these anomalies and previously recorded anomalies of the hypothenar muscles, and notes that: “Both fascicles arose from the flexor retinaculum and the antebrachial fascia; one was inserted into abductor digiti minimi and the other on the proximal phalanx of the 5th finger.”

J R Sañudo, R M Mirapeix, B Ferreira, A rare anomaly of abductor digiti minimi, J Anat. 1993 June; 182(Pt 3): 439–442.

Abductor digiti minimi exercises

Finger abduction

This exercise is designed to train the natural range of motion of the abductor digiti minimi by forcing it to abduct against resistance, in this case a small resistance band or elastic band.

Begin by finding an elastic band that is an appropriate size to fit your four fingers between, refer to the picture for a clearer understanding.

Once the elastic band is in place, keep your index, middle, and ring fingers as still as possible (some movement is inevitable) while abducting the little finger away from your other fingers.

Keep the movement smooth and controlled and do not apply so much resistance that the movement becomes strained or jerky.

Perform 10-20 repetitions on each hand and repeat for 3-4 sets.

Reference

Jenkins (2005), Sports science handbook. 1. A – H, Multi-Science Publishing