Multiscale Quantitative Imaging of Human Femoral Heads Using X-ray Microtomography

Abstract

Clinical diagnostic tools provide limited information on the underlying structural and mechanical properties of bone-tissue affected by degenerative and bone metabolic diseases. In-vivo bone failure studies provide limited information due to constraints such as X-ray dosage, cost and various other practicalities. In-vitro studies are thus required to enhance understanding of this phenomenon. The aims of this study were to use quantitative high-definition X-ray Micro-Tomography (XMT) to assess factors contributing to pathological and non-pathological bone failure and repair in relation to the mechanics of whole human femoral heads. XMT images of one normal and six pathological femoral heads were collected at 26 – 8.8 μm voxel resolution and evaluated to determine structural features; bone mineral concentration (BMC); and using image analysis, identify microcallus formations. In addition, in-vitro compression tests were carried out on specimens taken from regions with different anatomical loading. Bone quality was then related to the anatomical loading and BMC. Results from non-pathological tissue where used to establish a baseline for measurements of structural features. Microcallus formations where identified and used as markers to map the occurrence of bone damage. In osteoarthritic (OA) heads, the damage was found to be concentrated in localised clusters. Conversely, in the osteoporotic head damage was distributed homogeneously throughout the entire specimen. No significant difference in the BMC was observed, however there was a iii significant difference in the bone quality values between the non-pathological and pathological heads, and also between the pathologies. In-vitro mechanical testing revealed a difference in the mechanical properties of OA trabecular bone in relation to bone quality measurements but the samples exhibited no significant correlation to anatomical loading. X-ray Ultra Microscopy (XuM) at 200nm and 775nm voxel resolution was used to investigate the nano-morphology of individual trabeculae. The XuM images showed differences in bone structure and fewer osteocyte lacunae present close to fracture site. XuM also identified micro-cracks within trabeculae that were encased by microcallus formations. The application of novel quantitative high definition X-ray imaging to clinically relevant tissue at multiple length scales has provided new metrological data on the distribution of damage within pathological tissue. Insight into the vulnerability of diseased tissue to damage could ultimately lead to improved diagnosis from clinical radiographs.