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First Carpometacarpal Joint

articulatio carpometacarpalis pollicis

The first carpometacarpal (CMC) joint is a reciprocally concavo-convex saddle joint between the trapezium and the base of the first metacarpal, providing the greatest range of motion of any CMC joint. It allows flexion-extension (in the plane of the palm), abduction-adduction (perpendicular to the palm), and circumduction — the combination producing opposition. The joint is stabilised by the anterior oblique ligament (beak ligament, the primary stabiliser), dorsal radial ligament, and multiple secondary ligaments.

Region: Hand & Wrist

Clinical Relevance

Clinical Notes

First CMC osteoarthritis (basal joint arthritis, thumb CMC OA) is the most common site of hand OA in women, producing dorsal radial wrist pain reproduced by the grind test (axial load with circumduction). Conservative management includes splinting and corticosteroid injection. Surgical options include trapeziectomy with ligament reconstruction and tendon interposition (LRTI — Burton-Pellegrini), arthrodesis, and total CMC joint arthroplasty. Bennett fracture is an intraarticular fracture-dislocation of the thumb CMC where the dorsolateral metacarpal base displaces under the pull of APL while the anteromedial fragment remains attached to the anterior oblique ligament.

Pathology

Common Injuries & Conditions

Bennett Fracture at the First CMC Joint

Axial force on the partially flexed thumb metacarpal fractures the first CMC joint, displacing the main metacarpal fragment proximally and radially under APL pull while the small anteromedial fragment is held by the anterior oblique ligament; ORIF with percutaneous K-wires restores the joint surface and maintains reduction while the capsular-ligamentous healing occurs.