Extensor digiti minimi

Origin: Lateral epicondyle of the humerus via the common extensor tendon

Insertion: Extensor expansion at the base of the proximal phalanx of the digit (dorsal aspect)

Artery: Posterior interosseous artery (branch of the common interosseous artery, ultimately derived from the ulnar artery)

Nerve: Posterior interosseous nerve (C7, C8)

Action: Extension of the little finger at all joints (MCP, PIP, and DIP)

Antagonist: Flexor digiti minimi brevis

Description

1. Origin and course

The extensor digiti minimi is a slender muscle positioned medial to the extensor digitorum. It originates from the common extensor tendon at the lateral epicondyle of the humerus and receives additional fibers from the intermuscular septa separating it from adjacent muscles.

2. Tendon pathway and insertion

The muscle's tendon passes through a dedicated compartment within the dorsal carpal ligament (extensor retinaculum), separate from other extensor tendons. Upon reaching the dorsum of the hand, the tendon commonly bifurcates into two slips before inserting into the extensor expansion of the fifth digit.

3. Functional mechanism

The extensor digiti minimi functions as an extrinsic extensor of the fifth digit through its integration with the dorsal digital expansion (extensor hood). This mechanism enables coordinated extension of all three joints: the metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints.

The tendon's effectiveness is enhanced by its stabilization within the extensor mechanism through several key ligamentous components, including sagittal and lateral bands, retinacular, and triangular ligaments. These interconnected structures work synergistically to distribute and modulate the muscle's contractile force throughout the extensor hood, ensuring precise and controlled digit extension