The extensor digitorum communis, or EDC, is a primary muscle located in the forearm. Its main responsibility is to straighten the fingers and open the hand. This muscle is used for a wide range of daily activities, from releasing an object you are holding to gesturing, such as waving.
Anatomy and Location of the EDC Muscle
The EDC is a superficial muscle on the posterior, or back, side of the forearm. This placement makes it relatively easy to feel when you extend your fingers. The muscle originates from a common tendon attached to the lateral epicondyle of the humerus, the prominent bony bump on the outer part of your elbow.
As it approaches the wrist, the EDC muscle transitions into four distinct tendons. These pass through a protective sheath under a ligament at the back of the wrist called the extensor retinaculum. After crossing the wrist, the four tendons diverge across the back of the hand to attach to the index, middle, ring, and little fingers. They insert into the extensor expansions, which cover the tops of the finger bones.
Function of the EDC Muscle
The most direct action of the EDC muscle is the extension of the four medial fingers—the index, middle, ring, and little finger. This movement occurs primarily at the metacarpophalangeal joints, the main knuckles where the fingers meet the hand. It allows you to straighten your fingers from a fist, like when opening your hand to catch a ball.
Beyond extending the fingers, the EDC also assists in extending the wrist, helping to bend it backward at the wrist joint. The EDC is specifically innervated by the posterior interosseous nerve, a deep branch of the radial nerve. This connection allows the brain to command the muscle to contract and produce movement.
Common Injuries and Pain
Because of its constant use, the EDC is susceptible to overuse injuries. Repetitive motions that involve gripping, typing, or using hand tools can lead to strain and inflammation of the muscle and its tendon. This strain often manifests as pain where the muscle’s common tendon attaches to the elbow.
This condition is a primary contributor to lateral epicondylitis, more widely known as “Tennis Elbow.” The pain is a burning sensation or ache on the outer part of the elbow that can radiate down the back of the forearm and is often tender to the touch. The injury can also lead to a decrease in grip strength, making it difficult to hold objects securely. Resisted extension of the middle finger can reproduce the pain, which is a common diagnostic test.
Stretches and Strengthening Exercises
Maintaining the flexibility and strength of the EDC muscle can help prevent injury. A simple and effective stretch is the wrist extensor stretch. To perform this, keep your elbow straight and extend your arm in front of you with your palm facing down. Use your other hand to gently bend the outstretched hand downward, holding the stretch for 20-30 seconds. You should feel a mild pull on the top of your forearm.
For strengthening, wrist extensions with a light weight are beneficial. Sit with your forearm resting on a table or your thigh, with your hand and wrist extending off the edge, palm facing down. Holding a light dumbbell or a resistance band, slowly raise your hand upward to extend the wrist, then lower it back down. Start with very light or no weight to ensure proper form and stop if you experience any pain.