Muscle
Extensor indicis
Separate extension for the index finger
High-yield
Its tendon accompanies extensor digitorum through wrist compartment 4 and usually joins the index expansion on its ulnar side.
Overview
This deep forearm muscle adds an independent tendon to the index finger's extensor system. It supports pointing and other movements that separate the index finger from its neighbors.
Reference facts
- Origin
- Posterior distal ulna and adjacent interosseous membrane
- Insertion
- Dorsal extensor expansion of the index finger
- Action
- Extends the index finger and makes a smaller contribution to wrist extension
- Innervation
- Posterior interosseous nerve; predominantly lower cervical contributions, with C7-C8 commonly listed
- Blood supply
- Posterior interosseous arterial branches
Clinical correlation
Surgeons can transfer this tendon to restore thumb extension after an extensor pollicis longus rupture. The index retains its extensor digitorum tendon, although extension strength can decrease after transfer.
Frequently asked questions
What does the extensor indicis do?
The extensor indicis extends the index finger and makes a smaller contribution to wrist extension.
What nerve innervates the extensor indicis?
Posterior interosseous nerve; predominantly lower cervical contributions, with C7-C8 commonly listed.
Where does the extensor indicis attach?
Origin: Posterior distal ulna and adjacent interosseous membrane. Insertion: Dorsal extensor expansion of the index finger.
What is the blood supply of the extensor indicis?
Posterior interosseous arterial branches.