High Strain Rate Testing of Bovine Trabecular Bone

Abstract

In spinal vertebral burst fractures, the dynamic properties of the trabecular centrum, which is the central region of porous bone inside the vertebra, can play an important role in determining the failure mode. If the failure occurs in the posterior portion of the vertebral body, spinal canal occlusion can occur and ejected trabecular bone can impact the spinal cord resulting in serious injury. About 15% of all spinal cord injuries are caused by such burst fractures. Unfortunately, due to the uniqueness of burst fracture injuries, postinjury investigation cannot always accurately assess the degree of damage caused by these fractures. This research makes an effort to begin understanding the governing effects in this important bone fracture event. Measurements of the dynamic deformation response of bovine trabecular bone with the marrow intact and marrow removed using a modified split-Hopkinson pressure bar apparatus are reported and compared with quasistatic deformation response results. Because trabecular bone is more compliant and lower in strength than cortical bone, typical Hopkinson pressure bar experimental techniques used for high strain rate testing of harder materials cannot be applied. Instead, a quartz-crystal-embedded, split-Hopkinson pressure bar developed for testing compliant, low strength materials is used. Care is taken into account for the orthotropic properties in the bone by testing only along the principle material axes, determined through microcomputed tomography. In addition, shaping of the stress wave pulse is used to ensure a constant strain rate and homogeneous specimen deformation. Results indicate that the strength of trabecular bone increases by a factor of approximately 2-3 when the strain rate increases from 10(-3) s(-1) to 500 s(-1) and that the bone fractures beyond a critical strain.

The behavior of cancellous bone from quasi-static to dynamic strain rates with emphasis on the intermediate regime

“…Furthermore, the stress values are comparable to the literature dedicated to human cervical cancellous bone (Shim et al, 2005) compression from the upper intermediate regime (100/s) up to the dynamic regime, but are slightly higher than values for dynamic human tibial characterization (Teja et al, 2013). Data on tibial bovine bone (Pilcher et al, 2010) shows a similar range of ultimate stress values while the apparent Young's modulus has a higher range than in this study.…”

“…Whichever model is used, its fidelity suffers from a lack of representative data. Literature studies have primarily focused on quasi-static compression loadings (up to 0.1/s, equivalent to a brisk run (Burr and Allen, 2013)), while more recently some researchers have developed dynamic compression tests (10 2 -10 3 /s (Shim et al, 2005;Pilcher et al, 2010;Johnson, 2010)). While some authors have reported studies on the mechanical response of cancellous bone at intermediate strain rates (from 1/s (Halgrin, 2009) to 10/s (Carter and Hayes, 1977;Linde et al, 1991)), there is a general lack of data for this range, which is mainly due to experimental difficulties experienced with traditional devices used in experimental mechanics, i.e.…”

Rheological behavior of fresh bone marrow and the effects of storage

“…The results of this study provide more accurate properties for computational modeling of bone marrow mechanics within whole bones or trabecular bone samples (Pilcher et al, 2010). Computational models employing Newtonian fluid properties suggest that cells within marrow are subjected to shear stress that could affect mechanobiological response (Birmingham et al, 2013;Coughlin and Niebur, 2012;Dickerson et al, 2007).…”

Intermediate strain rate behaviour of cancellous bone: Links between microstructural and mechanical properties

“…Cancellous bone is known to be strain rate dependent [20]. The results are lower than those for the dynamic characterization of bovine tibia [21] but higher than human tibia results [3]. regarding E app , σ y & σ u while the yield and ultimate strains appear higher at 1/s.…”

“…Literature studies have focused on extreme loadings (low [1] and recently high [2,3] strain rates). The intermediate strain rate (ISR) regime (1 and 10/s) has been characterized [4,5] but the observed scatter was not investigated or linked to the upper ISR limit (100/s) and extreme strain rates.…”