Wrist kinematics after limited intercarpal arthrodesis

Two limited intercarpal fusions, scapho-trapezial-trapezoidal and scapho-capitate, were simulated in six fresh human cadaver wrists by means of two Herbert screws. By use of a biplanar radiographic measurement system, the relative kinematic behavior of selected carpal bones, before and after the simulated limited fusions could be analyzed. Both scapho-trapezialtrapezoidal and scapho-capitate fusions produced a similar reduction in global range of motion and comparable effects on the relative intracarpal motion. In both fusions, a significant reduction in relative motion at the lunocapitate joint was recorded. The scaphoid, being fused to the distal carpal row, was shown to lose its role in the adaptative mechanism that allows preservation of articular congruency to the always changing space between the distal carpal row and the radius. After both types of fusion, increased sliding motion of the lunate on the radius was found. These kinematic changes are likely to enhance shear stresses on the lunate and tension on the surrounding ligaments, potentially diminishing long-term functional results.