Flexor Digiti Minimi Brevis of Hand

What is Flexor Digiti Minimi Brevis

The flexor digiti minimi brevis (FDMB) is a short intrinsic hand muscle located on the ulnar side of the palm, at the base of the 5th digit or little finger. It belongs to the hypothenar group of muscles with the abductor digiti minimi and opponens digiti minimi.

Anatomy

Location and Attachments

Origin	The hook of hamate and the attached flexor retinaculum
Insertion	Ulnar side of the 5th proximal phalangeal base

Origin

The short muscle arises from the hook of the hamate bone, a carpal bone located on the distal carpal row. Some part of the muscle also originates from the flexor retinaculum adjacent to the hamate.

Insertion

From its point of origin, the muscle fibers course distally, towards the ulnar side of the hand, over the 5th metacarpophalangeal joint. In its course, the muscle belly narrows down into a small tendon to insert into the medial or ulnar side of the base of the 5th digit’s proximal phalanx.

Relations With Surrounding Muscles and Structures

As mentioned above, it is a hypothenar muscle on the medial side of the palm. The adductor digiti minimi muscle is superior and medial to the flexor digiti minimi brevis. On the other side, the opponens digiti minimi muscle lies lateral and inferior to it. Together, these three muscles form the hypothenar eminence.

A gap formed by the proximal ends of the flexor digiti minimi brevis and abductor digiti minimi allows passage to the deep branches of the ulnar nerve and artery.

Function

Action

Flexion of the little finger at the metacarpophalangeal joint

As suggested by its name, the muscle’s primary function is flexing the little finger at the metacarpophalangeal joint. It means this muscle helps fold the little finger (towards the palm) at its base.

Additionally, the muscle helps with opposition of the little finger, which means bringing it opposite to the other digits. Another function is the lateral rotation of the finger, where the little finger moves away from the rest of the fingers and palm.

The flexor digiti minimi brevis’s actions oppose those of the extensor digiti minimi muscle, which is considered its antagonist.

Innervation

Nerve

Deep branch of the ulnar nerve (C8, T1)

Along with the other two hypothenar muscles, the flexor digiti minimi brevis is innervated by the deep branch of the ulnar nerve originating from nerve roots C8 and T1.

Blood Supply

Artery

Deep palmar branch of the ulnar artery