Opponens digiti minimi muscle of hand

Origin and insertion

Opponens digiti minimi is a small, triangular muscle that arises from the hook of hamate bone (convex part) and the flexor retinaculum of the hand. It inserts into the ulnar aspect of metacarpal bone 5 and the adjacent palmar surface. The perforating branch of ulnar artery and the deep branch of ulnar nerve divide opponens digiti minimi into two lamellae, or bands. 

Relations

Opponens digiti minimi is located deep to flexor digiti minimi brevis and abductor digiti minimi muscles. Along its course, opponens digiti mini partly blends with the surrounding muscles, often fusing with the neighboring hypothenar muscles. 

Opponens digiti minimi is closely related to two neurovascular structures. The deep palmar branch of ulnar artery courses deep, or directly through opponens digiti minimi, before anastomosing with the radial artery. The deep branch of ulnar nerve also perforates opponens digiti minimi on its way towards the flexor tendons.

Innervation

All hypothenar muscles, including opponens digiti minimi, are innervated by the deep branch of ulnar nerve, which stems from the brachial plexus (C8, T1 spinal nerves).

Blood supply

Opponens digiti minimi is supplied by the deep palmar branch of ulnar artery and the deep palmar arch, which is the terminal branch of the radial artery.

Functions 

Opponens digiti minimi acts on the fifth carpometacarpal joint to cause finger flexion and lateral rotation, which help to deepen the hollow of the palm. In addition, when these actions are combined with flexion and lateral rotation at the metacarpophalangeal and interphalangeal joints, the result is opposition of the little finger with the thumb. This happens when trying to touch your thumb and fifth digit on the palmar side of the hand. 

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The function of these actions becomes evident when trying to grip curved or irregular objects, such as a ball. To improve the grip, the little finger is tightly opposed to the ball. Therefore, it is used by baseball players, rugby players, and in various ‘throwing sports’ on a daily basis.