Why Cervical Vertebrae Do Not Fracture – A Biomechanical Approach Using Loading Tests on Human Vertebrae of A 79-Year-Old Body Donor.

Abstract

Abstract Purpose: Bone structure alters with increasing age. Material and structural properties are both important for bone strength. Despite having an ageing society, there is a paucity of data from elderly subjects in terms of these parameters. The aim of the present study was to conduct comparative examinations of the structure and material properties of the cervical spine (CS), the thoracic spine (TS) and the lumbar spine (LS), in order to identify both structural and biomechanical differences between the segments of the spine. Methods: We examined central bone cylinders of vertebral bodies C1 to L5 from a 79-year-old body donor in regards to their bone volume fraction (BVF), trabecular thickness (Tb.Th.), separation (Tb.Sp.), trabecular orientation (SMI) and degree of anisotropy (DA). Samples were obtained from all vertebrae with a Jamshidi needle®, and were prepared with a damp cloth in an Eppendorf reaction vessel (1.5 ml). The investigations were performed with a micro-CT device (SKYSCAN 1172, RJL Micro & Analytic GmbH, Germany). Existing deformities and fractures were registered with quantitative computed tomography (QCT). The load tests of the vertebral bodies C1 to L5 were performed on a servo-hydraulic testing machine (MTS 858, MTS Systems Cooperation, Eden Prairie, USA). Results: Regarding BVF (p=0.003), Tb.Th. (p=0.041) and SMI (p=0.012) statistically significant differences were found in the different spinal column sections. The force per area was significantly higher in the CS than in the TS and LS (CS vs. TS, p=0.022; CS vs. LS, p<0.001; TS vs. LS, p=0.012). Conclusion: Due to their unique microarchitecture cervical vertebrae are less prone to fractures than thoracic and lumbar vertebrae. Among the reasons are the higher BVF and Tb.Th. of the cervical vertebrae compared to other vertebrae. Furthermore, the SMI of the CS has more plates than rods. Thus, the CS is characterized by specific features, whose causes must be determined in further investigations.