Overview
The carpus of the dog has seven bones arranged in a proximal and a distal row. Together they form the carpal joint (articulatio carpi), a composite joint in which most movement happens at the antebrachiocarpal level, less at the middle carpal level and almost none at the carpometacarpal level. In the standing dog the carpus is slightly hyperextended.
Proximal row
- Radial carpal bone (os carpi radiale): the largest carpal bone, formed by the fusion of the radial, intermediate and central carpal bones. It articulates with most of the distal radius.
- Ulnar carpal bone (os carpi ulnare): lateral; articulates with the radius and the styloid process of the ulna.
- Accessory carpal bone (os carpi accessorium): projects palmarly from the lateral side and acts as a lever for the flexor carpi ulnaris; it is palpable behind the carpus.
Distal row
First to fourth carpal bones (ossa carpalia I–IV), from medial to lateral. The fourth is the largest and articulates with metacarpals IV and V; the first is the smallest and supports metacarpal I (the dewclaw).
Clinical relevance
- Carpal hyperextension injury: rupture of the palmar ligaments and fibrocartilage after a fall or jump makes the dog walk on the back of the carpus; it is usually treated by arthrodesis.
- Fractures of the accessory carpal bone are typical of racing greyhounds.
- Carpal laxity (hyperextension or flexion deformity) is seen in growing puppies and usually resolves with controlled exercise.
In this model the carpal bones come from a CT scan of another dog (Scan the World), scaled and positioned below the radius and ulna; they are shown as one block per side.