Synchrotron X-ray Tomography Study of Bone-implant Integration

Sammanfattning: Implant loosening is a recurring problem in the field of orthopedics, typically resulting in a physical and financial burden for the patient. Proper integration of orthopedic implants within host bones is a fundamental requirement for the successful function and limited risk of failure of implants which, in-vivo, must support various loading conditions. This implant fixation is highly dependent on the amount and quality of the bone formed around the implant post-surgery. Previous studies have used mechanical loading, combined with lab or medical source X-ray imaging at macro- and micro-scale, as well as digital volume correlation (DVC), to successfully characterize the structural and mechanical properties of the bone-implant interface of small animals ex-vivo. Nevertheless, these studies had limitations due to imaging artifacts, low image resolution and small sample sizes. In this study, both the number of specimens and the image resolution were increased compared to previous studies. Here, 21 rat tibiae were implanted with polyether ether ketone (PEEK) implants and imaged at high resolution using X-ray synchrotron micro-Computed Tomography (micro-CT) during in situ pull-out of the implants. The PEEK implants were filled with a Calcium sulfate-hydroxyapatite (CaS/HA) based bone cement or with a combination of CaS/HA and bioactive molecules (zoledronic acid (ZA) and recombinant human bone morphogenic protein-2 (rhBMP-2)) known to promote bone formation. The experiments were conducted prior to the start of this degree project. The focus of this degree project lay on processing and analyzing the collected data. The quality of the bone-implant interface was quantitatively assessed based on the mechanical properties obtained from the pull-out experiment. Quantitative evaluation was achieved by using the CT data to visualize and quantify the bone formation around the implants. A qualitative assessment of the interface was also performed, analyzing the internal strain distribution through DVC analysis of micro-CT images. Additionally, the use of DVC as a tool to identify cracks and deformations in the peri-implant bone, in loadsteps prior to failure, was investigated. Combining PEEK implants with bioactive molecules improved the overall mechanical resistance of the bone-implant interface. Bone volume fraction increased significantly by 250.4%. Furthermore, DVC served as useful tool in visualizing the strain distributions in bone specimens under loading, successfully indicating local regions of deformation and fracturing within the loaded samples, prior to complete failure. Both untreated and treated samples showed comparable modes of failure; the bone failing at the threads and the thin trabecular bone surrounding the implant. Improving newly formed peri-implant bone quality and quantity could lead to an increased quality of life for patients and a decrease of the financial burden caused by orthopedic surgery.