Extensor Digitorum Communis
The Extensor Digitorum Communis, also called the Common Digital Extensor, is one of four muscles in the craniolateral antebrachial group. It is the second most cranial in this group. Bordered by the Extensor Carpi Radialis cranially and the Extensor Digitorum Lateralis caudally.
Full Length Extensor Digitorum Communis Anatomy Video
It originates from the lateral epicondyle on the humerus, cranial and proximal to the lateral collateral ligament of the elbow. A small portion of it originates from the antebrachial fascia. At its origin it is fused with the Extensor Carpi Radialis in front of it by a shared aponeurosis. An aponeurosis is a flat sheet of connective tissue that connects muscles to other muscles (or sometimes muscles to bones).
The Extensor Digitorum Communis is actually four muscle bellies. They run down the cranial lateral radius, and it is a fairly small muscle. Small in comparison to the Extensor Carpi Radialis in front of it, but larger than the Extensor Digitorum Lateralis behind it. One third of the way down the radius three of the four muscle bellies transition into tendons. Half way down the radius the final muscle transitions into a tendon, this is the tendon that will go to digit 2.
These four tendons are very closely grouped and appear as one. Sometimes they are fused together, especially tendons 3 and 4. Either way they are enclosed together in the synovial sheath. This synovial sheath starts a bit distal to the tenomuscular junction and runs down usually to around the carpometacarpal joint. As the compound tendon runs down the antebrachium it crosses over the Abductor Pollicis Longus tendon. Then at the distal radius it passes through the lateral distal sulcus of the radius.
At the level of the radiocarpal joint the compound tendon subdivides into four smaller tendons. As they cross over the dorsal carpus they are held in place by the Extensor Retinaculum. The tendons of the Extensor Digitorum Communis can be palpated on the dorsal lateral carpus, lateral to the Extensor Carpi Radialis tendon.
At the carpometacarpal joint the tendons diverge and one of each of these tendons goes down the corresponding metacarpal bone to the distal phalanges (P3) of digits 2 through 5. Inserting into the extensor processes of the distal phalanges (P3).
The Extensor Digitorum Communis is one of the longest tendons in the dog's forearm.
Its main function is to extend all four of the main digits. It is called the 'Extensor Digitorum Communis' because it extends all of the main digits. 'Communis' means 'common'. It is common, it goes to all the main digits.
It also plays a role in carpal extension. Primarily to stabilize the carpus.
Like all of the muscles in the craniolateral antebrachial group it is innervated by the radial nerve.