Volar Intercalated Segment Instability Secondary to Medial Carpal Ligamental Laxity

The midcarpal joint is stabilized by active, longitudinal compressive forces which produce balancing lateral volar flexion and medial dorsiflexion moments on the lunate. Laxity of the capitotriquetral ligament results in failure of the triquetral-hamate joint to produce a dorsiflexion moment, and the unbalanced volar flexion moment generated by the scaphoid produces volar intercalated segment instability (VISI). Four patients are reported to demonstrate the mechanics, clinical manifestations, and treatment of VISI.