title: Mechanisms of reduced implant stability in osteoporotic bone.
abstract: The determining factors for the fixation of uncemented screws in bone are the bone-implant interface and the peri-implant bone. The goal of this work was to explore the role of the peri-implant bone architecture on the mechanics of the bone-implant system. In particular, the specific aims of the study were to investigate: (i) the impact of the different architectural parameters, (ii) the effects of disorder, and (iii) the deformations in the peri-implant region. A three-dimensional beam lattice model to describe trabecular bone was developed. Various microstructural features of the lattice were varied in a systematic way. Implant pull-out tests were simulated, and the stiffness and strength of the bone-implant system were computed. The results indicated that the strongest decrease in pull-out strength was obtained by trabecular thinning, whereas pull-out stiffness was mostly affected by trabecular removal. These findings could be explained by investigating the peri-implant deformation field. For small implant displacements, a large amount of trabeculae in the peri-implant region were involved in the load transfer from implant to bone. Therefore, trabecular removal in this region had a strong negative effect on pull-out stiffness. Conversely, at higher displacements, deformations mainly localized in the trabeculae in contact with the implant; hence, thinning those trabeculae produced the strongest decrease in the strength of the system. Although idealized, the current approach is helpful for a mechanical understanding of the role played by peri-implant bone.
authors.affiliation: Institute for Biomechanics, ETH Zurich, Zurich, Switzerland. druffoni@ethz.ch
authors.forename: D
authors.initials: D
authors.lastname: Ruffoni
authors.forename: R
authors.initials: R
authors.lastname: Müller
authors.forename: G H
authors.initials: GH
authors.lastname: van Lenthe
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws; D001842:Bone and Bones / Q000502:physiology; D003198:Computer Simulation; D004548:Elasticity; D020342:Finite Element Analysis; D006801:Humans; D015233:Models, Statistical; D009985:Orthopedics / Q000379:methods; D010024:Osteoporosis / Q000534:rehabilitation* / Q000628:therapy; D011474:Prosthesis Design; D013314:Stress, Mechanical