Time-lapsed imaging of implant fixation failure in human femoral heads.

The failure mechanisms of bone-implant constructs are still incompletely understood, because the role of the peri-implant bone in implant stability is unclear. We hypothesized that implant fixation failure is preceded by substantial peri-implant bone failure. A new device was developed that combines mechanical testing of large bone-implant constructs with high-resolution peripheral quantitative computed tomography, following the principles of image-guided failure assessment (IGFA). In this study, we investigated the push-in failure behavior of dynamic hip screws (DHS) implanted in human cadaveric femoral heads. For the first time the fixation failure of a clinically used implant in human trabecular bone could be experimentally visualized at the microstructural level. The ultimate force was highly correlated with the peri-implant bone volume fraction (R(2)=0.85). We demonstrated that primary fixation failure of DHS implants was accompanied by trabecular bone failure in the immediate peri-implant bone region only. Such experimental data are crucial to enhance the understanding on the quality of the bone-implant interface and of the trabecular bone in the process of implant fixation failure. We believe that this newly developed device will be beneficial for the development of new implant designs, especially for use in osteoporotic bone.