CT--Compatible Hexapod Robot for Multi--Directional Mechanical Testing of Bone by Digital Volume Correlation

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Within 30 years, 1 in 4 Canadians is expected to have osteoarthritis, yet we still understand little about the basic mechanical properties of bone in the context of osteoarthritis, as well as other degenerative bone conditions. Typically with osteoarthritis, the joint undergoes adaptive changes as the cartilage degrades. However, treatment is hampered because differences between normal and osteoarthritic patients are poorly understood, and our current inability to model subject-specific bone quality prevents us from being able to predict how bone will remodel in the presence of synthetic components such as a joint implant. Moreover, we are currently not able to consider the subject-specific bone quality to select an optimal implant type or material that minimizes mechanical stresses in the bone and promotes remodeling. High internal bone stresses may lead to small fractures that progress to cause loosening of components and eventual failure, which impedes our ability to understand the processes that affect people who have degenerative bone diseases and how to best address them.  Our basic knowledge of the osteoarthritic process and its treatments can be vastly improved by understanding the underlying mechanics and load transfer of the human joint. The principal applicant holds a NSERC Discovery grant to develop and validate bone predictive models by experimentally applying forces to bone samples while viewing their internal structure in a high resolution micro-CT scanner. Currently, this work is being performed with a customized multi-axis Stewart platform style robot, which has a load limit only capable of performing non-destructive bone tests. Moreover, the current robot has no closed-loop load control, which limits the investigations that are possible. This Research Tools and Instruments grant will allow the acquisition of a new hexapod loading robot with a much higher load range for destructive testing, and with closed-loop multi-axis load control that will allow the research team to perform investigations with physiologically accurate loading vectors. Mechanical testing of human bone is essential to improve our understanding of the natural mechanisms of the osteoarthritis process in relation to normal bone. This work will also permit us to improve our models of compromised bone quality in patients requiring joint replacements, and to predict risk of fracture. A better way to measure how bone internally transfers forces would improve our understanding of these natural processes and allow us to validate computer models that are meant to predict bone remodeling. Ultimately, this work will provide new methods to assess mechanical performance of newly developed biomaterials and implantable devices, including joint implants used in the treatment of osteoarthritis and other degenerative disease processes.