A finite-element analysis of Kienbock's disease

A finite-element analysis model of the lunate was established using geometrical data obtained from cadaveric bones. The lunate cortex was modelled with triangular and quadrilateral elements and its intraosseous structure was represented either as a homogenous elastic structure or as an anisotropic network of cortical bone beams (trabeculae) with different orientations and thicknesses. Compressive loads applied to the metacarpus were distributed in the carpus against the fixed radius and ulna. The ulnar variance had a strong influence on the ratios radiolunate/ulnolunate total load and peak pressures. The distribution of internal stresses was markedly affected by the lunate uncovering index. The evolution of a simulated incomplete fracture was dramatically influenced by morphological parameters: with positive ulnar variance, the fracture did not progress, but in the presence of three associated conditions, negative ulnar variance, a high lunate uncovering index and angulated trabeculae, the fracture progressed and the proximal part of the lunate collapsed. This study supports the concept that some lunates are predisposed to Kienböck's disease because their anatomy induces abnormal internal stresses, which allow an incomplete fracture to progress, under heavy loading conditions, and cause progressive collapse and localised trabecular osteonecrosis.