metacarpalia

Metacarpalia refers to the five metacarpal bones of the hand, which form the intermediate region between the carpal bones of the wrist and the proximal phalanges of the fingers. They are numbered I to V from the thumb side (lateral) to the little finger (medial). Each metacarpal has a proximal base, a slender shaft, and a distal head. The bases articulate with the distal row of carpal bones and with adjacent metacarpals to form the carpometacarpal (CMC) joints and intermetacarpal joints.

The carpometacarpal articulations vary by bone. The base of the first metacarpal articulates with the trapezium and forms a saddle-type carpometacarpal joint that enables the thumb’s wide range of movements, including opposition. The bases of the second through fifth metacarpals articulate with the distal carpal row, with the second typically in contact with the trapezoid and capitate, the third with the capitate, and the fourth and fifth with the capitate and hamate.

The distal ends of the metacarpals enlarge to form the heads, which articulate with the proximal phalanges at the metacarpophalangeal joints. The bodies of the metacarpals are connected by intermetacarpal joints, contributing to the hand’s mobility and grip.

In clinical anatomy, metacarpal fractures are common, notably fractures of the neck of the fifth metacarpal (boxer's fracture) and intra-articular fractures at the base of the first metacarpal (Bennett fracture).