An analysis of femoral component stem design in total hip arthroplasty.

UNLABELLED: A comparative study of the various aspects of the design of the femoral components of total hip replacements was done using three-dimensional finite-element stress analysis. The aspects of deisgn that were considered included: length, cross-sectional size, and material properties of the stem; presence or absence of a medial collar; and material properties of the cement. We found that increasing the length of the stem generally increased the stress present in the stem while decreasing the stress present in the cement. Increasing the cross-sectional size of the stem decreased the stress in both the stem and the cement. Decreasing the modulus of elasticity of the stem material decreased the stress in the stem but increased the stress in the cement. Increasing the modulus of elasticity of the cement decreased the stress in the stem and increased the stress in the cement. Contact of the collar of a femoral prosthesis with the calcar femorale increased the longitudinal component of stress within the region of the calcar femorale. CLINICAL RELEVANCE: The mechanical longevity of a total joint reconstruction is related to the stress distribution throughout the prosthesis, cement, and bone. The stress distribution is related to a number of factors, including the design of the prosthetic components (for example, stem size, stem length, stem modulus of elasticity, and cement modulus of elasticity). Reducing the stresses in prosthetic components to minimize the risk of failure can be accomplished only through systematic analysis of all components of the reconstruction.