Opponens Digiti Minimi

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Description

Opponens digit minimi (ODM) is an intrinsic muscle of the hand. It's a triangular muscle that extends between the hamate bone (carpal bone) and the 5th metacarpal bone. It forms the hypothenar muscle group together with the abductor digiti minimi and flexor digit minimi brevis, based on the medial side of the palm (hypothenar einence). These muscles act together in moving the little finger. The opponens digiti minimi is responsible for flexion, lateral rotation and opposition of the little finger.

Intrinsic muscles of the hand

Origin

Hook of hamate and flexor retinaculum

Insertion

Inserts into the medial border of 5th metarcarpal bone

Nerve

Deep branch of the ulnar nerve, which stems from the brachial plexus (C8, T1 spinal nerves)

Artery

Blood supply is by the deep palmar branch of ulnar artery and deep palmar arch, which is the terminal branch of the radial artery

Function

Opponens digiti minimi acts to oppose the little finger to the thumb by:

• Flexion of the fifth metacarpal
• Lateral rotation of the carpometacarpal joint of the fifth digit
• Lateral rotation of the metacarpophalangeal joint of the fifth digit

Clinical relevance

The oponones digiti minimi which forms part of the intrinsic muscles provides fine motor movement of the hand. This is usually seen when trying to grip round or irregular objects such as a ball. The ulnar nerve which supplies the hypothenar muscles including opponens digiti minimi passes through the hook of hamate and pisiform bone (Guyon's canal), compromise to the nerve at this point leads to atrophy of the ODM with a resulting weakness in moving the 5th finger. There's also numbness, tingling, and pain in the 4th and 5th finger that comes with ulnar nerve entrapment. See also Cyclist palsy.