Apparent viscoelastic anisotropy as measured from nondestructive oscillatory tests can reflect the presence of a flaw in cortical bone

Abstract

There is evidence that damage, viscoelastic stiffness properties, and postyield mechanical properties are related in bone tissue. Our objective was to test whether presence of a flaw would have an influence on the apparent viscoelastic properties of bone. Examining the effect of flaw orientation on apparent viscoelastic properties and utilization of dynamic mechanical analysis (DMA) as a nondestructive means for detection of damage were our secondary objectives. Cortical bone beams (2 x 2 x 19 mm) machined from the cranial cortex of the radii of six Warhill sheep were used. The specimens were placed in a DMA machine and baseline measurements of storage modulus (E1) and loss factor (tan delta), once for loads in the craniocaudal and once in the mediolateral directions, were performed using a three-point bending configuration for a frequency range of 1-10 Hz. Craniocaudal/mediolateral measurement ratio was calculated as a measure of anisotropy for tan delta and E1. After cutting a thin through-thickness macroscopic notch on the caudal surface at the center of each beam, oscillatory tests were repeated. Two-way repeated measures analysis of variance followed by Tukey's test was used with group (craniocaudal, mediolateral, notched craniocaudal, and notched mediolateral measurements) and frequency as factors. Regression analysis and analysis of covariance were used for examining the relationship between viscoelastic parameters and frequency. Tan delta and E1 were not different between craniocaudal and mediolateral measurements before the flaw was introduced (p > 0.8 and p = 1, respectively). In the presence of the flaw, tan delta was significantly increased (p < 0.003) whereas E1 was significantly reduced (p < 0.001) for craniocaudal measurements. Tan delta and E1 were nearly isotropic in the tested directions before the introduction of a flaw into the bone tissue. Introduction of a flaw resulted in increased tan delta and E1 anisotropy. Presence of a notch resulted in a significant increase in tan delta anisotropy with increasing frequency. In conclusion, we have demonstrated that cortical bone tissue exhibits a different apparent viscoelastic behavior in the presence of a flaw and depending on the flaw's orientation. Our finding that the presence of a notch and its orientation can be detected by nondestructive DMA suggests that in vivo techniques may be developed for detection of cortical bone damage.

The effect of yield damage on the viscoelastic properties of cortical bone tissue as measured by dynamic mechanical analysis

“…1), scanning a frequency range of 1-10 Hz (in 0.2 Hz increments). 24,28 Storage modulus, E1 (for dynamic tests, equivalent to Young's modulus) and loss factor, tan d (an indication of the amount of energy dissipated by viscous mechanisms relative to energy stored in the elastic component) were measured for each of the cranio-caudal (cranial bending: load applied to the cranial surface), caudal-cranial (caudal bending: load applied to the caudal surface), medio-lateral (medial bending: load applied to the medial surface) and latero-medial (lateral bending: load applied to the lateral surface) bending directions.…”

“…The results of a previous experiment 24 were reanalyzed as described above in order to compare with the current results. In that experiment, all test parameters were the same as the current, except that the specimens were resubjected to a DMA test after cutting a defect at the center of beams instead of introducing damage using mechanical loading.…”

“…We have demonstrated in our previous work that the presence of a flaw in bone tissue can be detected using frequency analysis of dynamic properties from nondestructive oscillatory tests. 24 Although the use of a machined flaw provided information on the effect of a large (on the order of 1 mm) and highly concentrated defect with known geometries on the viscoelastic behavior of bone, it is not clear whether this can be extrapolated to mechanically induced damage. In this study, we examined the effect of minimal mechanical damage (created by loading bone tissue just beyond yield) on the subsequent viscoelastic behavior of cortical bone tissue.…”

“…24 This allowed us to recalculate the parameters of that study in a way consistent with the current design and to perform a more comprehensive statistical analysis. We also revisit an experiment where data were available from bone specimens that were damaged using fatigue loading and subjected to ultrasound measurements before and after fatigue damage.…”

Analysis of anisotropic viscoelastoplastic properties of cortical bone tissues

“…Fresh ulna specimens were tested using dynamic mechanical analysis in the temperature range from -50°C to 80°C, at a constant frequency of 1 Hz (Mano, 2005). Based on the evidence that damage, viscoelastic, stiffness and post-yield mechanical properties are related in bone tissue, the influence of the presence of a flaw on apparent viscoelastic properties of cortical bone tissue was studied in (Yeni et al, 2004) Specimens -for all of our studies -were cut from fresh bovine femur bones (aged 1.5-2 years). The mid-part of five femora (diaphysis) were extracted using a handsaw.…”