BIOMECHANICAL ANALYSIS OF LIMITED INTERCARPAL FUSION FOR THE TREATMENT OF KIENBOCKS-DISEASE - A 3-DIMENSIONAL THEORETICAL-STUDY

Although several types of intercarpal fusion have been advocated for t he treatment of Kienbock's disease, the clinical outcome of each proce dure is still inconclusive. The joint load and ligament tension based on a three-dimensional model were measured to determine which intercar pal fusion procedures unload the lunate and whether they alter the for ce transmission through the entire wrist joint. Ten theoretical models of wrists were used to simulate three different operative procedures: capitate-hamate fusion, scapho-trapezial-trapezoidal fusion, and scap hocapitate fusion. A discrete element analysis technique was used to p erform these investigations. The joint force and ligament tension of n ormal wrists and of simulated operative procedures were calculated acc ording to the deformation of each spring element, simulating the artic ular cartilage and the carpal ligaments. Scaphocapitate and scapho-tra pezial-trapezoidal fusions significantly decreased the joint force at the radiolunate joint and the lunocapitate joint compared with the int act wrist. In contrast, these fusions significantly increased this val ue at the radioscaphoid joint in comparison with the intact wrist. In the midcarpal joint, scaphocapitate fusion also increased the joint fo rce at the scapho-trapezial-trapezoidal joints and at the triquetral-h amate joint, whereas scapho-trapezial-trapezoidal fusion increased it at the scaphocapitate joint. Capitate-hamate fusion yielded no signifi cant changes of the joint forces through the entire wrist joint. In th e analysis of ligament tension, scaphocapitate and scapho-trapezial-tr apezoidal fusions significantly decreased the tension only in the dors al scapholunate ligament. These findings demonstrate that scaphocapita te and scapho-trapezial-trapezoidal fusions are effective in decompres sing the lunate. By contrast, capitate-hamate fusion is ineffective in reducing lunate compression. Although scaphocapitate and scapho-trape zial-trapezoidal fusions are recommended for the treatment of Kienbock 's disease, clinicians should consider that the increase of force tran smission through the radioscaphoid and the midcarpal joints may lead t o early degenerative changes after these procedures have been performe d.