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First Metacarpal

os metacarpale primum

The first metacarpal is the shortest and most mobile of the metacarpals, articulating with the trapezium at the first CMC joint (saddle joint allowing wide range of motion) and with the thumb proximal phalanx at the thumb MCP joint. The base of the first metacarpal is the site of Bennett fracture (intraarticular CMC fracture-dislocation) and Rolando fracture (comminuted CMC fracture). The diaphysis is shorter and broader than the other metacarpals.

Region: Hand & Wrist

Clinical Relevance

Clinical Notes

Bennett fracture is the most common first metacarpal fracture, an intraarticular fracture-dislocation of the first CMC joint: the main metacarpal fragment is pulled proximally and radially by the abductor pollicis longus, while the anteromedial fragment remains held to the trapezium by the anterior oblique ligament. Closed reduction and percutaneous K-wire fixation or ORIF restores the articular surface. Rolando fracture (Y-shaped or T-shaped comminuted CMC fracture) has worse outcomes than Bennett. First metacarpal shaft fractures from direct trauma are treated by closed reduction and immobilisation.

Pathology

Common Injuries & Conditions

Bennett Fracture-Dislocation of the First Metacarpal Base

Axial force on the partially flexed thumb metacarpal fractures the CMC joint intraarticulary, with the main fragment displaced proximally under APL pull while the anteromedial fragment is held by the volar ligament; closed reduction and percutaneous K-wire fixation from the first metacarpal to the trapezium maintains reduction while healing occurs.