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.