Stress distribution in the ulna following a hinged elbow arthroplasty. A finite element analysis

The failure rates for total elbow arthroplasty, in comparison to those for hip arthroplasty, are quite high, and a precise understanding of the underlying causes still remains elusive. The presence of abnormal stresses is a known factor that accelerates loosening of hip and knee arthroplasties. Although a large number of biomechanical studies have led to a better understanding of elbow joint kinetics, very little is known about the stress distribution in this joint. The implantation of a Coonrad humeral component increases stresses in the bone and cement adjacent to the stem tip and hinge regions. An analysis of implanted ulnar stresses and a comparison of those stresses to implanted humeral stresses would improve our understanding of hinged elbow arthroplasty. For this reason, the distribution of mechanical stresses in the ulna are investigated in this study. Using a specially developed casting and sectioning technique, three-dimensional finite element meshes were obtained from an intact human cadaver ulna and an ulna fitted with a Coonrad prosthesis. The material properties were derived from values presented in the literature. Stress distributions in response to axial compression, axial torque, and anteroposterior (AP) force were computed. The cancellous bone and cement regions adjacent to the stem tip of the prosthesis exhibited higher stresses than those in the same regions of the intact case. The higher stresses in the ulna with an implanted prosthesis, as compared to the intact model, might initiate loosening or failure of the prosthesis. The stresses in the cortical bone region adjacent to the prosthesis head were decreased. This is consistent with the clinical observations of bone atrophy following total elbow arthroplasty.(ABSTRACT TRUNCATED AT 250 WORDS)