Overview
The metacarpus has five metacarpal bones (ossa metacarpalia I–V), numbered from medial to lateral. Each has a proximal base, a body and a distal head. Metacarpal I is short and does not reach the ground; II to V lie side by side, III and IV being the longest and the main weight-bearing bones, II and V slightly shorter.
Key features
- Base (basis): articulates with the distal row of carpal bones and with the neighbouring metacarpals.
- Body (corpus): slender and slightly curved, convex dorsally.
- Head (caput): articulates with the proximal phalanx at the metacarpophalangeal joint. A sagittal ridge on its palmar side fits between the two proximal sesamoid bones, which lie in the palmar part of the joint capsule.
Clinical relevance
- Metacarpal fractures usually follow trauma (being stepped on, falls, car accidents) and often involve several bones; fractures of the weight-bearing III and IV need stabilisation more often than those of II and V.
- Stress fractures and luxations of the metacarpophalangeal joints are seen in racing and working dogs.
In this model the metacarpal bones come from a CT scan of another dog (Scan the World), scaled and positioned below the carpus.