Extensor Digitorum Lateralis

The Extensor Digitorum Lateralis is a small muscle on the lateral antebrachium. It is one of four muscles in the cranial lateral group. Bordered by the Extensor Digitorum Communis cranially and the Extensor Carpi Ulnaris (Ulnaris Lateralis) caudally.

Watch my full length youtube video on the Extensor Digitorum Lateralis.

It consists of two muscle bellies. The first muscle belly originates from the cranial edge of the lateral collateral ligament of the elbow joint. The second muscle belly originates from the lateral epicondyle on the humerus. Together they run down the lateral antebrachium. Hence its name 'lateralis'. It is a small muscle, about half the size of the Extensor Digitorum Communis. About half way down the antebrachium the muscle bellies transition into tendons. The more cranial tendon is smaller and the more lateral/caudal tendon is larger. Both tendons stay together, usually wrapped in a synovial sheath. 

At the distal antebrachium they pass through the groove between the distal ends of the radius and ulna. As they pass over the dorsal lateral carpus they go under the Extensor Retinaculum. This tendon can be palpated on the lateral carpus.

Below the carpus the tendons diverge. The more caudal tendon goes down metacarpal 5 to the proximal phalanx (P1) of digit 5. Here it unites with the tendon of the Extensor Digitorum Communis and together they insert into the extensor process of the distal phalanx (P3) of digit 5. They also have some minor connection into the dorsal surfaces of the proximal ends of the proximal phalanx P1 and the middle phalanx P2.

The cranial tendon splits into two and descends down the 3rd and 4th metacarpals. At the proximal phalanges (P1) these tendons also merge with the tendons of the Extensor Digitorum Communis and insert mainly into the extensor processes on the dorsal distal phalanges (P3) of digits 3 and 4.

Its main function is to extend the digits, but it still plays a small role in extending the carpus as well. 

This muscle is very tight and has long tendons and short muscle fibers. Which means that it may store elastic energy during movement. However, its location on the lateral forearm suggests that it may be more important for stabilization and to absorb ground force reactions. 

Injury to this muscle is not commonly reported. Though due to its size and redundancy of its action in the Extensor Digitorum Communis and other surrounding muscles, injury to this muscle could easily go unnoticed.

Like all the muscles in the craniolateral group it is innervated by the radial nerve.