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Second through Fifth Carpometacarpal Joints

articulationes carpometacarpales II-V

The second through fifth carpometacarpal (CMC) joints are plane synovial joints between the distal carpal row (trapezoid, capitate, hamate) and the bases of the second through fifth metacarpals. They allow very limited gliding motion: the second and third CMC joints are essentially immobile (index and long finger metacarpals are anchored tightly for grip stability); the fourth allows approximately 15 degrees and the fifth approximately 25 degrees of flexion-extension, enabling the ring and little fingers to flex more deeply for power grip.

Region: Hand & Wrist

Clinical Relevance

Clinical Notes

The fourth and fifth CMC joints are the most clinically relevant: boxer's fractures involve the metacarpal neck of the fifth (and sometimes fourth) after punching, and are distinct from CMC fracture-dislocations. CMC fracture-dislocations of the fourth and fifth metacarpals (more mobile, higher force required) produce dorsal metacarpal base displacement and require ORIF or percutaneous K-wire fixation. The hamate hook sits at the ulnar side of the fourth-fifth CMC junction and fractures separately from CMC dislocations.

Pathology

Common Injuries & Conditions

Fourth and Fifth CMC Fracture-Dislocation

High-energy axial force along a clenched fist produces fourth and fifth metacarpal base fracture-dislocation at their carpometacarpal joints, with dorsal displacement of the metacarpal bases and ring and little finger shortening; CT confirms the fracture pattern and ORIF or percutaneous K-wire fixation restores the CMC alignment.