The effect of femoral stem cross-sectional geometry on cement stresses in total hip reconstruction.

A three-dimensional numerical stress analysis of a prosthesis-cement-proximal femur system was performed to reveal functional differences of total hip femoral component stems with varying cross-sectional shapes. The analysis was performed on stem cross-section shapes similar to many of the variations presently available in femoral components. The results indicate that the predicted levels of stress in the cement are often close to critical (i.e., failure) levels. The magnitude and mode (i.e., compression versus tension) of loading in the cement are significantly affected by the stem cross-sectional shape. Particular attention is paid to the stress in the cement within the proximal portion of the structure. High compression stresses in the cement are shown to result from prostheses with narrow medial surfaces and small area moments of inertia. High cement tensile stresses result from prostheses with small area moments of inertia. A large region of cement compression results from prosthesis cross-sections with relatively large anterior-posterior dimensions about their lateral aspect. Desirable stress distributions result from prostheses with broad medial surfaces and even broader lateral surfaces.