Effect of modular head seating on the cement-stem interface strength of femoral prostheses

This study tested the hypothesis that modular head seating in situ reduces the cement-stem interfacial strength. Femoral prostheses were implanted in eight pairs of cadaveric femurs; one femur of each pair received a stem for which the modular head was seated by dropping a weight from a given height (treated); the contralateral femur received a nonseated stem (control). Transverse sections were cut from four standardized locations on each implanted femur, and the yield shear stress and ultimate shear stress of the interface were determined from push-out tests. There was no significant difference in cement-stem interfacial strength between seated and nonseated prostheses. These results suggest that seating modular heads in situ has no deleterious effect on the acute interfacial strength of cemented femoral implants.