Overview
The carpus (ossa carpi) is the group of short bones between the radius and ulna proximally and the metacarpus distally. In cattle it has six bones in two rows: four in the proximal row and two in the distal row, because carpal bone I is absent and carpal bones II and III are fused. The carpal joint, called the "knee" in lay usage for large animals, combines three levels: antebrachiocarpal, middle carpal and carpometacarpal. Most flexion takes place at the first two; the carpometacarpal joint is almost rigid.
Bones
- Proximal row, from medial to lateral:
- Radial carpal bone (os carpi radiale): articulates with the radius.
- Intermediate carpal bone (os carpi intermedium): articulates with the radius.
- Ulnar carpal bone (os carpi ulnare): articulates with the lateral styloid process of the ulna.
- Accessory carpal bone (os carpi accessorium): palmar and lateral, articulates with the ulnar carpal bone; acts as a lever for the flexor and extensor carpi ulnaris muscles.
- Distal row:
- Fused second and third carpal bone (os carpale II et III): a single medial bone, the largest of the row.
- Fourth carpal bone (os carpale IV): lateral.
- Both articulate with the large metacarpal bone (fused III and IV).
Clinical relevance
- Carpal hygroma: a fluctuant swelling on the dorsal surface of the carpus, from inflammation of the subcutaneous precarpal bursa. It results from repeated trauma when lying down and getting up on hard floors or insufficient bedding, and is common in housed dairy cows. Where brucellosis is endemic it has been associated with Brucella abortus.
- Septic arthritis in calves: the carpus is one of the joints most often involved in polyarthritis secondary to navel infection.
- Congenital flexural deformity: calves born with the carpus flexed that cannot extend it, because of contracture of the flexor tendons.
- Skin lesions on the dorsal carpus in animals that spend long periods kneeling, such as those with painful claws.