Extensor indicis
Musculus extensor indicis
Also known as: extensor indicis proprius, EIP
A small deep extensor that allows the index finger to be extended independently, as in pointing. It is a common donor for tendon transfer.
Overview
Extensor indicis arises from the posterior surface of the distal ulna and the interosseous membrane. It passes through the 4th compartment deep to the extensor digitorum tendons and joins the extensor expansion of the index finger, usually on the ulnar side of the extensor digitorum tendon. It gives the index finger independent extension (pointing) and assists wrist extension. Because the index finger keeps extensor digitorum as a back-up, extensor indicis can be transferred, for example to restore thumb extension after EPL rupture.
Anatomy
- Origin
Posterior surface of the distal ulna and the interosseous membrane.
- Insertion
Extensor expansion of the index finger.
- Action
Extension of the index finger (pointing); assists wrist extension.
- Innervation
Posterior interosseous nerve.
- Nerve roots
C7–C8
- Arterial supply
Posterior interosseous artery (and the anterior interosseous artery).
Function
- Extends the index finger independently
- Assists wrist extension
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.