Instability patterns of the wrist.

Carpal instabilities are generally the result of a hyperextension injury. The deformities are mediated through the internal compressive force supplied by the musculotendinous units and are dependent on the extent of injury as well as the precise structures that are disrupted. The scaphoid inherently tends to palmar flex. It will pull the lunate with it if the lunotriquetral integrity has been interrupted, and conversely the lunate and triquetrum will dorsiflex if the scapholunate integrity is disrupted. If the integrity of the oblique external ligaments, particularly the volar (palmar) radiolunate, is disrupted, the entire carpus has a tendency to translate ulnarly. Carpal instabilities are invariably associated with weakness, limitation of motion, and pain.