Opponens

Opponens is a term used in anatomy to describe muscles that oppose the action of a digit, bringing it into contact with another digit. The name comes from the Latin oppōnere, meaning to place opposite. In humans, the best-known opponens muscles are in the hand, where they contribute to fine motor control. The concept also appears in the foot for muscles that oppose the big toe, though the hand examples are the most prominent.

In the hand, the two primary opponens muscles are the opponens pollicis and the opponens digiti minimi. The opponens pollicis originates from the flexor retinaculum and nearby carpal bones such as the trapezium, and inserts along the radial side of the first metacarpal. Its action is to oppose the thumb by medially rotating and flexing the metacarpal, bringing the thumb toward the palm. It is innervated by the recurrent branch of the median nerve (C8–T1).

The opponens digiti minimi originates from the hook of the hamate and the flexor retinaculum, and inserts along the ulnar border of the fifth metacarpal. Its action brings the little finger into opposition with the thumb, aiding in grip. It is innervated by the deep branch of the ulnar nerve (C8–T1).

Clinical relevance: Loss of opposition due to nerve injury impairs grip and precision. Median nerve palsy can weaken opponens pollicis, while ulnar nerve palsy can affect opponens digiti minimi, contributing to diminished opposition and grip strength.