Tendon of extensor indicis

The tendon of extensor indicis muscle allows for independent and precise control of the index finger. Formed from its deep muscle belly in the forearm, the tendon enters the fourth dorsal compartment at the wrist, passing beneath the extensor retinaculum alongside the extensor digitorum tendons. It then courses along the ulnar side of the extensor digitorum tendon to the index finger, ultimately inserting into the ulnar aspect of the extensor expansion (dorsal digital expansion) of the index finger, typically at the metacarpophalangeal (MCP) joint. This enables extension of the index finger at all its joints (MCP, PIP, DIP) and assists in wrist extension.