Finite element stress analysis of the wrist joint without and with an endoprosthesis.

The finite element analysis method was used to obtain the lateral deformation profile and values of the von Mises stress in the cortical and cancellous regions of the various bones in models of a selected space in the coronal plane of a human wrist joint, without and with a prosthesis. The prosthesis was the metacarpal component of the Trispherical design of the total wrist joint arthroplasty. The models included all the bones, the associated network of ligaments, and the intervening soft muscle tissue. Each type of model was completely constrained along its entire proximal surface and subjected to either a static point force (in the axial compressive or anteroposterior tensile direction) acting at the center of the distal tip of the third metacarpal cortical bone. For the models containing the prosthesis, a parametric study was conducted involving the method of anchorage of the prosthesis to the contiguous bones and the material of fabrication of the prosthesis. It was found that: (1) the axial force produces lower stresses in the bones compared with the anteroposterior one; (2) no clear-cut case can be advanced, from the stress viewpoint, for press-fitting the prosthesis to the contiguous bones rather than using bone cement for such anchorage; and (3) any alloy with modulus of elasticity in the 79 to 196 GPa range and Poisson's ratio of about 0.3 may be used to fabricate the prosthesis. The approximations used and the associated limitations of the work are fully discussed, as are the design implications and clinical significance of the results.