The different contributions of cortical and trabecular bone to implant anchorage in a human vertebra

The quality of the peri-implant bone and the strength of the bone-implant interface are important factors for implant anchorage. With regard to peri-implant bone, cortical and trabecular compartments both contribute to the load transfer from the implant to the surrounding bone but their relative roles have yet to be investigated in detail. However, this knowledge is crucial for the better understanding of implant failure and for the development of new implants. This is especially true for osteoporotic bone, which is characterized by a deterioration of the trabecular architecture and a thinning of the cortical shell, leading to a higher probability of implant loosening. The aim of this study was to investigate the relative biomechanical roles of cortical and trabecular bone on implant pull-out stiffness in human vertebrae. The starting point of our investigation was a micro-computed tomography scan of an adult human vertebra. The cortical shell was identified and an implant was digitally inserted into the vertebral body. Pull-out tests were simulated with micro-finite element analysis and the apparent stiffness of the system with various degrees of shell thickness and bone volume fraction was computed. Our computational models demonstrated that cortical bone, although being very thin, plays a major role in the mechanical competence of the bone-implant construct.