Abstract
Better understanding of the local deformation of the bone network around metallic implants subjected to loading is of importance to assess the mechanical resistance of the bone-implant interface and limit implant failure. In this study, four titanium screws were osseointegrated into rat tibiae for 4 weeks and screw pullout was conducted in situ under x-ray microtomography, recording macroscopic mechanical behavior and full tomographies at multiple load steps before failure. Images were analyzed using Digital Volume Correlation (DVC) to access internal displacement and deformation fields during loading. A repeatable failure pattern was observed, where a ∼300–500 μm-thick envelope of bone detached from the trabecular structure. Fracture initiated close to the screw tip and propagated along the implant surface, at a distance of around 500 μm. Thus, the fracture pattern appeared to be influenced by the microstructure of the bone formed closely around the threads, which confirmed that the model is relevant for evaluating the effect of pharmacological treatments affecting local bone formation. Moreover, cracks at the tibial plateau were identified by DVC analysis of the tomographic images acquired during loading. Moderate strains were first distributed in the trabecular bone, which localized into higher strains regions with subsequent loading, revealing crack-formation not evident in the tomographic images. The in situ loading methodology followed by DVC is shown to be a powerful tool to study internal deformation and fracture behavior of the newly formed bone close to an implant when subjected to loading. A better understanding of the interface failure may help improve the outcome of surgical implants.
Highlights
Metal implants are commonly used in surgery to e.g., stabilize bone fractures or replace joints or teeth
This study investigates local damage in the bone around an implant during pullout, through concurrent x-ray tomography and mechanical loading followed by image analysis using Digital Volume Correlation (DVC)
We found a typical failure pattern through an envelope of bone that detached from the trabecular structure, suggesting that fracture was initiated close to the screw tip and propagated at some distance away from the implant surface
Summary
Metal implants are commonly used in surgery to e.g., stabilize bone fractures or replace joints or teeth. The mechanical performance of the interface has until recently been assessed macroscopically during in vitro pullout tests, e.g., comparing bone volume fractions with obtained loaddisplacement data (Iijima et al, 2013; Shea et al, 2014; Raina et al, 2019). Such experimental data can be coupled with numerical models to investigate and predict the mechanical stability of implanted screws (Wirth et al, 2011; Chevalier et al, 2018). The trabecular bone structure is complex, and the understanding could be improved by investigating how the material deforms locally around an implant while being subjected to loading
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