Overview
Its belly lies lateral to the extensor carpi radialis. The tendon crosses the dorsal carpus in a synovial sheath and runs down the dorsal surface of the third metacarpal bone. Since the horse has a single functional digit, it reaches the third phalanx undivided. At the level of the first phalanx it receives, on each side, the extensor branches of the interosseus medius (suspensory ligament).
Origin
Lateral epicondyle of the humerus and adjacent parts of the radius and ulna.
Insertion
Extensor process of the third phalanx (processus extensorius), with minor attachments on the dorsal surface of the first and second phalanges.
Action
Extends the joints of the digit and the carpus.
Innervation
Radial nerve (n. radialis).
Clinical relevance
- With radial nerve paralysis the horse cannot extend the digit: it stands with the fetlock knuckled forward.
- Rupture of the common digital extensor tendon occurs in newborn foals, often together with flexural deformities: there is a swelling on the dorsolateral carpus and the foal tends to knuckle at the fetlock.