Extensor indicis

The extensor indicis (Latin: musculus extensor indicis) is a relatively flat, narrow muscle of the forearm that extends between the ulna and the phalanges of the second finger. It belongs to the posterior compartment of the forearm muscles, lying in the second (deep) layer. The extensor indicis acts at all joints of the index finger.

Origin

The extensor indicis muscle originates from the distal one-third of the posterior surface of the ulna and interosseous membrane of the forearm.

Insertion

The extensor indicis descends to reach the second finger. It inserts on the bases of the middle and distal phalanges of the second digit of the hand.

Action

The extensor indicis muscle extends the second finger at the metacarpophalangeal and interphalangeal joints of the index finger.

Innervation

The extensor indicis is innervated by the posterior interosseous nerve, which is a branch of the radial nerve (C7, C8).

Blood supply

The extensor indicis muscle receives arterial blood supply from the anterior and posterior interosseous arteries. Both are branches of the common interosseous artery.