Classification of carpal instability.

A classification of carpal instability is presented based on anatomic and kinematic characteristics of the wrist. Three main types of instability are recognized. Lateral carpal instability may occur between the scaphoid and the trapezium-trapezoid, the scaphoid and the capitate, and the scaphoid and the lunate. Scapholunate dissociation or rotatory subluxation of the scaphoid is the most frequent representative of this type. Medical carpal instability may take place between the triquetrum and the lunate, or the triquetrum and the hamate. Dissociation between lunate and triquetrum results in static forms of instability, while disruption of triquetrohamate support leads to dynamic forms of instability. Proximal carpal instability may lead to disruption at the level of the radiocarpal joint or at the level of the midcarpal joint.