Keywords: morphology, regional mechanical characteristics, micro-computed tomography, micro finite element analysis.

To fully understand and predict the mechanical behaviour of bones, not only morphological characteristics but also mechanical characteristics such as structural modulus should be investigated. Several researchers have studied the mechanical characteristics of vertebrae. However, there have been few studies on regional morphology and the mechanical characteristics of vertebrae. Gong et al. [1] analysed regional variations in vertebral trabecular. Keller et al. [2] examined regional variation in the mechanical characteristics of lumbar vertebral trabecular bone from the effects of disc degeneration.

For this study, twelve thoracic vertebrae were obtained from 85 year old female and 48 year old male cadavers. The transverse plane images with 35&mu#mu;m resolution were scanned using the micro computed tomography (Micro-CT, Skyscan-1076, Skyscan, Belgium) system. Bones in the scanned images were divided into three layers, the superior, middle, and inferior layers, on vertical axis. Each layer had five regions, the anterior, posterior, right, left, and central regions. The structural parameters were calculated based on the images obtained. The μFEA was used to investigate the mechanical characteristics of vertebral trabecular bone. Two dimensional image data were converted into specimens of three dimensional voxel structures which were cubes with side length 4mm by using Bionix3.3 (Cantibio Co., Korea) software. The regression analysis was used to investigate the correlation between structural parameters and structural moduli using SPSS 12 (SPSS, USA).

The BV/TV and Tb.N in the central region were bigger than those in other regions in the same layer. The BV/TV in the right column were similar to those in the left column. The BV/TV in the posterior column were bigger than those in anterior column. The BV/TV in all layers of the 48 year old male specimens were bigger than in that of the 85 year old female specimens. By contrast, Tb.Th in all layers of the 85 year old female specimens was bigger than that of the 48 year old male specimens. The BV/TV and Tb.Th in a middle layer of 85 year old female bone and in a inferior layer of a 48 year old male bone were bigger than those in the other regions.

For most specimens, the reaction force and structural moduli in the 85 year old female specimens were bigger than those in the 48 year old male specimens. Reaction forces and structural moduli of the central region in both the 85 year old female and the 48 year old male were bigger than those of other regions in the same layer. Those of the middle layer in the 85 year old female were bigger than those of any other layers. However, those of the inferior layer in the 48 year old male were bigger than those of any other layers.

In this study, a significant correlation between SMI, Tb.Th and BV/TV and mechanical strength was shown. BV/TV in specimens of the 48 year old male was bigger than that in the 85 year old female, and Tb.Th in specimens of 85 year old male was thicker than that in the 45 year old female in all layers. These results suggested an age-related compensation process. The structural parameter in the 45 year old male was higher than that in 85 years female, and the changes in the structural parameters in the inferior layer had an opposite tendency to those in the other layers. These results showed that morphology and mechanical characteristics in a whole vertebral bone were not represented by a part of the vertebral bone. Previous researchers into regional variation in vertebral bone surgically cut each vertebral bone. In this study, however, each vertebral bone was virtually cut within a stimulated test, as was the scanning of the whole vertebral bone. The present study also examined using the micro-CT, to rule out potential pathological changes which had occurred by surgically cutting specimens, and investigated more regional variations in the identical specimens. Further study should investigate regional variations in morphology and mechanical characteristics using more vertebrae bone or regions. In conclusion, this study investigated and showed the region-related variation in thoracic vertebral bone.

1

He Gong, Ming Zhang, Hiu Yan Yeung, Ling Qin, "Regional variations in microstructural properties of vertebral trabeculae with aging", J Bone Miner Metab, Vol.23, pp.174-180, 2005. doi:10.1007/s00774-004-0557-4

2

Tony S. Keller, PhD, Tommy H. Hansson, MD, PhD, Adam C. Anram, MD, Dan M. Spengler, MD, and Manohar M. Panjabi, PhD, DTech, "Regional variations in the compressive properties of lumbar vetebral trabeculae: effects of disc degeneration", Spine, Vol.14, pp.1012-1019,1989

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