Mixed-mode failure strength of implant-cement interface specimens with varying surface roughness

Aseptic loosening at the implant-cement interface is a well-documented cause of failure in joint arthroplasty. Traditionally, the strength of the implant-cement interface is determined using uni-axial normal and shear loading tests. However, during functional loading, the implant fixation sites are loaded under more complex stress conditions. For this purpose, the strength of the implant-cement interface under mixed-mode tensile and shear loading conditions was determined in this study using interface specimens with varying interface roughness. For the lowest roughness value analyzed (R(a)=0.89 mum), the interface strength was 0.40-1.95 MPa at loading angles varying between pure tension and shear, whereas this was 4.90-9.90 MPa for the highest roughness value (R(a)=2.76 mum). The interface strength during pure shear (1.95-9.90 MPa) was substantially higher than during pure tension (0.58-6.67 MPa). Polynomial regression was used to fit a second-order interpolation function through the experimental interface strength data (R(2)=0.85; p