Kinetic analysis of carpal stability during grip.

When the wrist is grasping an object, at least four mechanisms of carpal stabilization are involved-one for each carpal row (proximal and distal), one for the midcarpal joint, and one for the radiocarpal joint. These mechanisms are based on the general principle that, under load-bearing conditions, any bone tends to rotate into a specific direction depending upon several factors, including the position of the wrist at the time of loading, the direction of the forces being transferred, and the inclination and shape of the articular surfaces on which the bone stands. Such an attempted displacement is initially guided and later neutralized by appropriately oriented ligaments, with which a new equilibrium is achieved. An injury or disease affecting any one of these mechanisms results in a specific type of carpal instability, depending upon which mechanism(s) has been violated. Only through a thorough understanding of these mechanisms of wrist stabilization will our ability to successfully treat these problems be enhanced.