Overview
The carpus (ossa carpi) is the group of short bones between the radius and ulna proximally and the metacarpal bones distally. In the cat, as in the dog, it has seven bones in two rows. The carpal joint allows very wide flexion and, together with rotation of the forearm, gives the cat's paw great handling ability.
Bones
- Proximal row:
- Radial carpal bone (os carpi intermedioradiale): the largest, formed by fusion of the radial and intermediate bones; articulates with the radius.
- Ulnar carpal bone (os carpi ulnare): lateral, articulates with the ulna.
- Accessory carpal bone (os carpi accessorium): projects palmarly as a lever; the flexor carpi ulnaris and the extensor carpi ulnaris insert on it.
- Distal row: carpal bones I to IV, from medial to lateral, which articulate with the metacarpal bones. Bone IV is the largest.
Associated structures
- Carpal pad (torus carpeus): on the palmar surface, over the accessory carpal bone; it does not touch the ground at a normal walk.
- Carpal vibrissae: a tuft of long tactile hairs proximal to the carpal pad, characteristic of the cat. They signal contact of prey with the paw.
- Palmar ligaments and palmar fibrocartilage: resist hyperextension of the carpus.
Clinical relevance
- Carpal hyperextension: rupture of the palmar ligaments after a fall or a jump lets the carpus sink to the ground; it is treated by arthrodesis.
- Luxations and fractures of the carpal bones after trauma.
- Osteoarthritis in older cats.