Triquetrohamate and triquetrolunate instabilities (medial carpal instability).

Anatomic and kinematic information needed for the understanding of radiocarpal instability is reviewed. Based on this, and on the concept of the columnar carpus, medial carpal instabilities are defined as those taking place between the triquetrum (medial column) and the hamate and lunate (central column). Therefore, two types of medial instability are recognized: triquetrohamate, across the mid-carpal joint, with loss of stability of the central column present only during ulnar or radial deviation (dynamic DISI and VISI), and triquetrolunate, producing the loss of the dorsiflexion influence of the triquetrum on the lunate and, consequently, a static type of VISI collapse. Treatment aimed at restoration of mid-carpal (triquetrohamate) and triquetrolunate dissociation is discussed, and illustrative cases presented.