Anatomy and Structure
The extensor digiti minimi (m. extensor digiti minimi) is located in the superficial layer of the posterior forearm.
- Origin (Origo) — The lateral epicondyle of the humerus (epicondylus lateralis), specifically via the common extensor tendon.
- Insertion (Insertio) — The dorsal digital expansion (extensor hood) of the fifth digit. As it courses toward the little finger, its tendon typically merges with the tendon of the extensor digitorum (m. extensor digitorum).
Topography and Neighboring Structures
The extensor digiti minimi lies within the superficial extensor group of the forearm. Other muscles in this layer include:
- Brachioradialis (m. brachioradialis);
- Extensor carpi radialis longus and brevis (m. extensor carpi radialis longus and m. extensor carpi radialis brevis);
- Extensor digitorum (m. extensor digitorum), whose tendons extend to digits II–V;
- Extensor carpi ulnaris (m. extensor carpi ulnaris);
- Anconeus (m. anconeus).
Carpal Tunnel and Compartments
As it crosses the wrist into the hand, the tendon of the extensor digiti minimi passes beneath the extensor retinaculum (retinaculum musculorum extensorum).
- Extensor Compartment — The tendon passes through its own dedicated 5th osteofibrous compartment beneath the extensor retinaculum.
- Contents — The compartment contains the tendon enclosed within its synovial sheath (vagina tendinis m. extensoris digiti minimi).
- Synovial Sheath Boundaries — The proximal border of the sheath is located at the level of the distal radioulnar joint. The distal border extends beyond the mid-shaft of the fifth metacarpal bone.
Blood Supply, Innervation, and Function
- Function — Extends the little finger (digit V) at the metacarpophalangeal and interphalangeal joints. It also assists in extension of the wrist.
- Blood Supply — Supplied by the posterior interosseous artery (a. interossea posterior).
- Innervation — Innervated by the radial nerve (n. radialis), originating from spinal cord segments C7–C8.
For comparison, other movements of the little finger are mediated by: abduction (C8–T1), opposition (C7–T1), and flexion of the proximal phalanx (C7–T1).