Kinematics of the wrist and its ligaments

Precise anatomic dissections of unembalmed physiologically intact cadaver specimens were carried out before proceeding with the kinematic investigations on further specimens. Carpal flexor and extensor tendons were used to move the wrist. The analysis of the carpal bone movements was performed according to the finite helical axis motion concept for increments of 10 degrees for each main carpal motion. Separate axes of rotation for each of the bones in the proximal carpal row were found; however, the axes for the lunate and triquetrum bones were close, and the magnitudes of rotation and translation almost equal. One finding was that the axes of rotation of the bones in the proximal carpal row often cross at some particular point. Because the axes of the scaphoid are differently oriented than those of the lunate and triquetrum, shear might occur during wrist motion. This indicates also that the scaphoid and lunate cannot be considered rigidly coupled elements. We also assume that the individual bones of the proximal carpal row self-align themselves as long as they are not constrained by torsion. Several potential mechanisms of flexion motion of the proximal carpal row during radioulnar deviations of the hand were considered. The ligament function is still an unsolved problem. Compensation mechanisms may mask clear correlations between a lesion and the instability pattern associated with it. The proximal carpal row should be studied as one system.