Extensor indicis
Extensor indicis is a narrow deep muscle of the back of the forearm that lets the index finger straighten on its own.
At a glance
- English
- Extensor indicis
- Latin (TA2)
- Extensor indicis
- System
- Muscle
- Region
- Upper limb
- Side
- Paired, left and right
About the extensor indicis
Extensor indicis belongs to the deep layer of the posterior forearm, where it lies beside and below extensor pollicis longus. It is the reason the index finger can point while the other fingers stay curled.
The muscle arises from the back of the lower part of the ulna and from the adjoining interosseous membrane. Its slim belly runs down towards the wrist under extensor digitorum, and its tendon passes beneath the extensor retinaculum in the fourth dorsal compartment along with the four tendons of that muscle. Over the back of the hand it runs medial to the index tendon of extensor digitorum and merges with it near the knuckle, so both end in the extensor expansion of the index finger.
Acting through the extensor expansion, it extends the index finger at the metacarpophalangeal joint and helps at the interphalangeal joints. Because it has its own belly, it allows independent extension of the index, as in pointing. It gives a small extra pull in extending the wrist. Like the other deep extensors it receives the posterior interosseous nerve. Its blood comes from the posterior interosseous artery, helped by the terminal part of the anterior interosseous artery after it passes to the back of the forearm.
Surgeons often borrow this tendon to replace a ruptured extensor pollicis longus, for example after a wrist fracture or in rheumatoid arthritis, because the index finger keeps good extension through extensor digitorum. Its tendon is also a landmark during surgery on the back of the wrist.
Attachments, action and supply
- Origin
- Posterior surface of the distal part of the ulna and the adjacent interosseous membrane.
- Insertion
- Extensor expansion of the index finger, blending with the index tendon of extensor digitorum on its medial side.
- Action
- Extends the index finger, allowing it to straighten independently; assists wrist extension.
- Nerve supply
- Posterior interosseous nerve (C7, C8).
- Blood supply
- Posterior interosseous artery and the terminal part of the anterior interosseous artery.
Anthromica
See the extensor indicis where it really sits, with every layer of the body around it.
- Every layer, one body. Peel from muscle to bone, nerve, vessel and organ, and turn it any way.
- English and Latin. Every structure named the way your exam names it.
- Quiz until it sticks. Short drills on the structures you keep missing.
Free to start. No card.
