Extensor Indicis, Posterior View

Description

Arising from the posterior ulna and adjacent interosseous membrane, the extensor indicis runs in the deep posterior compartment of the forearm, inferior to the extensor pollicis longus and medial to extensor digitorum. Its tendon passes deep to the extensor retinaculum through the fourth dorsal compartment alongside the extensor digitorum tendons, then continues distally on the dorsum of the hand to the second digit. At the level of the metacarpophalangeal joint it blends into the extensor expansion of the index finger, lying superficial to the metacarpals and phalanges and invested by dorsal fascia. Clear. Direct. That independent tendon slip is the anatomic basis for isolated index finger extension, a movement often tested in radial nerve palsy and posterior interosseous nerve syndrome when extension of the other digits may be partially preserved through extensor digitorum. For hand surgeons, the extensor indicis proprius is also a familiar donor in tendon transfer, commonly routed to restore extensor pollicis longus function after attritional rupture in rheumatoid arthritis or after distal radius fracture. The posterior perspective makes the relationships at the extensor retinaculum and dorsal compartments easy to teach and to map onto operative exposure. Use this artwork in gross anatomy and upper limb courses to distinguish deep from superficial extensors, in hand therapy materials explaining extensor hood mechanics, or in surgical and radiology publications discussing dorsal wrist compartments, intersection syndromes, and tendon transfer planning. Anatomical accuracy verified by SciePro's Medical Advisory Board.