Extensor digitorum

The extensor digitorumExtensor Back of forearm; extends fingers and wrist. is on the posterior (back) side of the forearm. It starts at the lateralAway from the midline of the body. epicondyle of the humerusLong bone of the upper arm; articulates with scapula at shoulder and radius/ulna at elbow.. It splits into four tendons that travel down the forearm. These tendons insert on the extensor expansions of fingers 2–5. It lies near the center of the posterior forearm and often fans out toward the back of the hand. On most models, you’ll notice it as the largest muscle mass. It sits just beneath the skinThe body’s largest organ, providing protection and regulation. on the back of the forearm. Other extensors surround it.

An everyday action that uses the extensor digitorum is spreading your fingers to type, play piano, or wave. It’s responsible for extending the fingers and the wrist. Overuse can happen during prolonged typing, texting, or playing string instruments. Repetitive finger and wrist extension can lead to lateral epicondylitis (commonly known as “tennis elbow”).

Origin

Lateral epicondyle of the humerus (via the common extensor tendon)

Insertion

Extensor expansions of digits 2–5 (middle and distal phalangesFinger bones; each finger has three (proximal, intermediate, distal), thumb has two. of fingers 2–5)

Actions

Extends fingers 2–5

Assists in wrist extension