Micromechanics of postmortem-retrieved cement-bone interfaces

The cement-bone interface plays an important role in load transfer between cemented implant systems and adjacent bone, but little is known about the micromechanical behavior of this interface following in vivo service. Small samples of postmortem-retrieved cement-bone specimens from cemented total hip replacements were prepared and mechanically loaded to determine the response to tensile and compressive loading. The morphology of the cement-bone interface was quantified using a CT-based stereology approach. Laboratory-prepared specimens were used to represent immediate postoperative conditions for comparison. The stiffness and strength of the cement-bone interface from postmortem retrievals was much lower than that measured from laboratory-prepared specimens. The cement-bone interfaces from postmortem retrievals were very compliant (under tension and compression) and had a very low tensile strength (0.21 +/- 0.32 MPa). A linear regression model, including interface contact fraction and intersection fraction between cement and bone, could explain 71% (p < 0.0001) of the variability in experimental response. Bony remodeling following an arthroplasty procedure may contribute to reduced contact between cement and bone, resulting in weaker, more compliant interfaces.