Giulia Cavazzoni ^1,2,3 Enrico Dall'Ara ^1,2 Marco Palanca ^1,2,3*

• ¹ Division of Clinical Medicine, School of Medicine and Population Health, The University of Sheffield, Sheffield, England, United Kingdom
• ² Insigneo Institute, Faculty of Engineering, The University of Sheffield, Sheffield, England, United Kingdom
• ³ Department of Industrial Engineering, School of Engineering, University of Bologna, Bologna, Italy

Bone spinal metastases disrupt the bone homeostasis inducing a local imbalance in the bone formation and/or resorption with consequent loss of the structural optimisation of the vertebrae and increase of the risk of fracture. Little is known about the microstructure of the metastatic tissue, the microstructure of the tissue surrounding the lesion, and how it does compare with vertebrae with no lesions observed on the biomedical images. A comprehensive assessment of the microstructural properties of the entire vertebral body can be obtained with micro-computed tomography. In this study we evaluated to what extent the vertebral body is affected by the presence of a metastatic lesion, the properties of the metastatic lesions and if the tissue surrounding the lesion has microstructural features similar to healthy tissue. Thirty metastatic vertebrae including lytic (N=12), blastic (N=10) and mixed (N=8) metastases, and twenty control vertebrae with no visible lesions on computed tomography were scanned with a microcomputed tomography (voxel size=39µm). Images were segmented and analysed to evaluate the microstructural properties in the entire vertebral body, in the lesion and in the bone surrounding the lesion. Microstructural properties evaluated on the entire vertebral bodies showed remarkable differences between metastatic and control vertebral bodies (P<0.034) in the bone volume fraction, trabecular thickness, degree of anisotropy, connectivity density and trabecular pattern factor. On the other hand, when the tissue surrounding the lesion was considered, no differences were found between metastatic and control vertebral bodies, except for differences in degree of anisotropy (P=0.008). All microstructural parameters measured in the regions including the lytic or the blastic metastases significantly differed (P<0.001) from those in the tissues surrounding the lesions. The lytic lesions minimally affected the regions closest to the metastases, with significant differences only in the connectivity density. Whereas blastic metastases also affected the trabecular separation, the bone surface density and the connectivity density in the closest tissue surrounding the lesion. In conclusion, most of the microstructural features of the trabecular bone in metastatic vertebrae were locally affected by lytic and blastic metastases, whereas the surrounding tissue showed a microstructure similar to that of adjacent vertebrae without visible lesions.