Author: Sanghita Bhattacharya

Publisher:

Published: 2011

Total Pages: 237

ISBN-13:

Relative motion at interacting implant surfaces will generate wear debris over time. Bio-tribological tests serve as an effective pre-clinical tool to investigate device wear characteristics. Wear debris evaluations for artificial discs are done in simulators using the currently published ASTM/ISO loading profiles. However, these tests can primarily compare wear related parameters of one disc design against another as opposed to an in vivo scenario. Additionally, these experiments are time consuming, expensive and labor intensive procedures. Current wear testing standards for artificial discs do not account for parameters such as the influence of anatomic structures and variations in the surgical procedures for disc placement. However, appropriate parametric mathematical modeling may help assess the contributions of these parameters to implant wear. The objective of this study is to address the above mentioned factors and to simulate in-vivo wear parameters as far as practicable. In this approach, the wear phenomena of the total disc replacement (for two different designs - metal on metal and metal on polymer) placed in a ligamentous functional spinal unit (FSU), as opposed the disc alone analyses conducted previously by other researchers was simulated. The models were further modified by sequential addition and removal of spinal structures in order to understand the role of each element with respect to the wear outcome. Furthermore, the effect of the implant placement was studied. This was followed by comparative analyses of load versus displacement control test methodology. A significant difference was noted between the implanted and standalone condition. The standalone test cases were in agreement with the published literature, while the implanted scenario replicated some of the retrieval failure modes. Lift-off at the device interface was observed at the implant interface which was found to be a function of facets and muscle forces. This phenomenon was also reported by other researchers, thus supporting our conclusion. The design factor was found to have more effect in comparison to the material combination. Also, implant positioning demonstrated that wear is sensitive to the device placement. Additionally, during the analysis displacement control mode led to higher wear in comparison to load control for both of the implants. We can summarize by stating that this study demonstrated the need to simulate implant wear in ligamentous finite element model in order to replicate failure modes that are observed during retrievals. Surgical factors are thus crucial with respect to the wear performance of the implant and so should be planned carefully.