The extensor indicis originates in the lower back of the ulna, just beneath the extensor pollicis longus. The interosseous membrane is placed next to it. It is a thin, long muscle in the deeper layers of the dorsal forearm. Its tendon performs the function of providing extension for the various index finger phalanges. This muscle travels across the fourth tendon compartment, with the extensor digitorum running parallel to it. The common link between this extensor of the index finger and the extensor of the little finger is that in both cases the tendon travels along the ulnar part of the tendon of the extensor digitorum. Both the extensors are without the oblique bands that connect the extensor digitorum tendons on the dorsal part of the hand. The key role of the extensor indicis is to provide an extension to the index finger. It also helps in extension of the midcarpal joints and the wrist. The disjointed extensors of the index and little fingers enable these two fingers to move more freely than the remaining fingers.
Written and medically reviewed by the Healthline Editorial Team
In Depth: Extensor indicis