Biomechanical analysis of limited intercarpal fusion for the treatment of Kienböck's disease: a three-dimensional theoretical study.

Although several types of intercarpal fusion have been advocated for the treatment of Kienbock's disease, the clinical outcome of each procedure is still inconclusive. The joint load and ligament tension based on a three-dimensional model were measured to determine which intercarpal fusion procedures unload the lunate and whether they alter the force 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 scaphocapitate fusion. A discrete element analysis technique was used to perform these investigations. The joint force and ligament tension of normal wrists and of simulated operative procedures were calculated according to the deformation of each spring element, simulating the articular cartilage and the carpal ligaments. Scaphocapitate and scapho-trapezial-trapezoidal fusions significantly decreased the joint force at the radiolunate joint and the lunocapitate joint compared with the intact wrist. In contrast, these fusions significantly increased this value at the radioscaphoid joint in comparison with the intact wrist. In the midcarpal joint, scaphocapitate fusion also increased the joint force at the scapho-trapezial-trapezoidal joints and at the triquetral-hamate joint, whereas scapho-trapezial-trapezoidal fusion increased it at the scapho-capitate joint. Capitate-hamate fusion yielded no significant changes of the joint forces through the entire wrist joint. In the analysis of ligament tension, scaphocapitate and scapho-trapezial-trapezoidal fusions significantly decreased the tension only in the dorsal scapholunate ligament. These findings demonstrate that scaph-ocapitate and scapho-trapezial-trapezoidal fusions are effective in decompressing the lunate. By contrast, capitate-hamate fusion is ineffective in reducing lunate compression. Although scaphocapitate and scapho-trapezial-trapezoidal fusions are recommended for the treatment of Kienbock's disease, clinicians should consider that the increase of force transmission through the radioscaphoid and the midcarpal joints may lead to early degenerative changes after these procedures have been performed.