Extensor Indicis

Joe Muscolino

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Extensor indicis of the deep posterior compartment of the forearm is seen. The extensor pollicis longus is ghosted in.

The Extensor Indicis is in the Deep Layer of the Posterior Compartment of the forearm. It is also a member of the Deep Distal Four Group; the deep distal four group is composed of:



  • Posterior ulna to the index finger (finger #2).
    • The proximal attachment is onto the distal 1/3 of the posterior ulna and interosseus membrane.
    • The distal tendon of extensor indicis joins into the ulnar side of the distal tendon of the extensor digitorum going to the index finger.



  • Extends the index finger at the metacarpophalangeal and proximal and distal interphalangeal joints.
  • Extends and radially deviates the hand at the wrist joint.
  • Supinates the forearm at the radioulnar joints.



  1. Other than the thumb, only the index and little fingers (fingers #2 and 5) have a second extrinsic extensor muscle. Having two extensor muscles allows the index finger to be so functional at physically pointing at and indicating things in the visual field.
  2. Both the extensor indicis and the extensor digiti minimi attach into the ulnar side of the distal tendon of extensor digitorum going to the respective finger.