Integrity of the stem-cement interface in THA: effects of stem surface finish and cement porosity.

No consensus exists for the optimal surface finish on cemented total hip prosthesis stems. The purpose of this study was to determine the effects of stem finish and interfacial cement porosity on the integrity of the stem-cement interface. Simulated stems made of Co-Cr, having polished or matte surfaces, at room temperature or heated to 37 degrees C, were cemented into Sawbones simulated femurs. Push out testing of the stem-cement interface was performed immediately after cement polymerization and after two aging periods in 37 degrees C saline or 37 degrees C air, and the extent of interfacial porosity at the stem-cement interface was determined. Polished stems exhibited an average 60% greater interfacial strength than that of matte stems initially and up to 240% after aging treatments. Cement porosity at the stem-cement interface and incomplete cement interdigitation into surface asperities on matte stems likely allowed saline penetration into the stem-cement interface during wet aging, resulting in a rapid decrease of shear strength. Stem preheating to 37 degrees C virtually eliminated interfacial pores and resulted in greater shear strengths regardless of surface finish. Polished stem surfaces with stem preheating provided the best interfacial shear strength and sealing ability against saline penetration into the stem-cement interface and could result in increased longevity of stem fixation.