The midcarpal joint is the articulation between the proximal carpal row (scaphoid, lunate, triquetrum) and the distal carpal row (trapezium, trapezoid, capitate, hamate). It is a compound joint with two compartments: the radial compartment (scaphoid-capitate-trapezoid) and the medial compartment (the hamate-triquetrum helicoid joint). Midcarpal joint motion contributes approximately 50% of total wrist flexion-extension and is the site of midcarpal instability.
Midcarpal instability (CIND — carpal instability non-dissociative) produces a painful clunk during wrist dart-throwing motion as the proximal carpal row snaps from flexion to extension at the midcarpal joint. The triquetrohamate helicoid joint is the kinematic engine driving the carpal rows from the ulnar side. DISI (dorsal intercalated segment instability) and VISI (volar intercalated segment instability) are midcarpal alignment patterns diagnosed on lateral wrist radiograph. Partial midcarpal arthrodesis (scapholunate-capitate fusion or triquetrohamate fusion) addresses specific midcarpal instability patterns.
Midcarpal instability from triquetrohamate ligamentous laxity produces a painful catch and clunk during ulnar deviation and dart-throwing motion as the proximal carpal row snaps abruptly into extension; the catch reproduces on physical examination with ulnar deviation against resistance and arthroscopy confirms midcarpal ligament laxity at the hamate-triquetrum joint.
