Links between mechanical behavior of cancellous bone and its microstructural properties under dynamic loading

Abstract

Previous studies show that in vivo assessment of fracture risk can be achieved by identifying the relationships between microarchitecture description from clinical imaging and mechanical properties. This study demonstrates that results obtained at low strain rates can be extrapolated to loadings with an order of magnitude similar to trauma such as car crashes. Cancellous bovine bone specimens were compressed under dynamic loadings (with and without confinement) and the mechanical response properties were identified, such as Young׳s modulus, ultimate stress, ultimate strain, and ultimate strain energy. Specimens were previously scanned with pQCT, and architectural and structural microstructure properties were identified, such as parameters of geometry, topology, connectivity and anisotropy. The usefulness of micro-architecture description studied was in agreement with statistics laws. Finally, the differences between dynamic confined and non-confined tests were assessed by the bone marrow influence and the cancellous bone response to different boundary conditions. Results indicate that architectural parameters, such as the bone volume fraction (BV/TV), are as strong determinants of mechanical response parameters as ultimate stress at high strain rates (p-value<0.001). This study reveals that cancellous bone response at high strain rates, under different boundary conditions, can be predicted from the architectural parameters, and that these relations with mechanical properties can be used to make fracture risk prediction at a determined magnitude.

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

“…The resulting correlations generally concur with the published quasi-static [23,24] and dynamic [7] published study. Trabecular separation, Tb.Sp, was not found to correlate with the Young's Modulus.…”

“…As suggested by the literature focused on quasi-static [23,24] and dynamic strain rates [7], an architecture effect (geometry, connectivity, topology, anisotropy) contributes to the experimental scatter observed in Fig. 3.…”

“…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. Detailed features of the micro-architecture of porous cancellous bone [6] have been linked to the quasi-static behaviour, to the dynamic and confined dynamic loading [7] to predict the fracture localization [8], the micro-damage [9] and the global mechanical response [10].…”

Influence of strain rate on the mechanical behaviour in tension of bovine cortical bone

“…6, a test with the SHTB is performed as follows: firstly, the hydraulic actuator (8) of maximum loading capacity of 600 kN is pulling the pretension high strength steel bar (9). The pretension stored in this bar is resisted by the blocking device (10). Secondly, the rupture of a fragile bolt in the blocking device, gives rise to a tensile mechanical pulse of 2,4 ms with linear loading rate during the rise time, propagating along the input (11) and the output (15) bars bringing to fracture the specimen (13).…”

“…It is widely reported [6] that the bone is strain rate sensitive while increasing the loading rate. This behaviour is relevant to cortical bone response in both tension [7] and compression [8][9][10].…”