Biomedical subjects

T P Pinilla

Publications and source records attributed to T P Pinilla.

3 recordsLinked to original sources

PubMed1999

Uniaxial yield strains for bovine trabecular bone are isotropic and asymmetric.

Although evidence suggests that yield strains for trabecular bone are isotropic, i.e., independent of loading direction, decisive support for this hypothesis has remained elusive. To explicitly test whether yield strains for trabecular bone are isotropic, compressive and tensile yield strains of 51 specimens of bovine tibial trabecular bone (0.41 +/- 0.08 g/cm3 [mean apparent density +/- SD]) were measured without end artifacts in on-axis (along the principal trabecular orientation) and off-axis (30-40 degrees oblique to on-axis) orientations. Yield strains for the on-axis and off-axis orientations were similar in tension (0.80 +/- 0.03% compared with 0.85 +/- 0.04%, p = 0.21) and compression (0.97 +/- 0.05% compared with 0.96 +/- 0.07%, p > 0.99); as expected, modulus and strength depended on loading direction. When considered with an ancillary experiment on bovine tibial trabecular bone that showed yield strains to be similar between on-axis and 90 degrees off-axis bone, these results firmly establish the isotropy of uniaxial yield strains for bovine tibial trabecular bone. This bone is of high density and has a strong, plate-type, anisotropic architecture. Therefore, yield strains for uniaxial loading are expected to be isotropic, or nearly so, for other types of dense trabecular bone, although further work is required to confirm this and to establish this behavior for bone of lower density.

Animals↗

PubMed1997

Systematic and random errors in compression testing of trabecular bone.

We sought to quantify the systematic and random errors associated with end-artifacts in the platens compression test for trabecular bone. Our hypothesis was that while errors may depend on anatomic site, they do not depend on apparent density and therefore have substantial random components. Trabecular bone specimens were first tested nondestructively using newly developed accurate protocols and then were tested again using the platens compression test. Percentage differences in modulus between the techniques (bovine proximal tibia [n = 18] and humerus [n = 17] and human lumbar spine, [n = 9]) were in the range of 4-86%. These differences did not depend on anatomic site (p = 0.21) and were only weakly dependent on apparent density and specimen aspect ratio (r2 < 0.10). The mean percentage difference in modulus was 32.6%, representing the systematic component of the end-artifact error. Neglecting the minor variations explained by density and specimen size (approximately 10%), an upper bound on the random error from end-artifacts in this experiment was taken as the SD of the modulus difference (+/-18.2%). Based on a synthesis of data taken from this study and from the literature, we concluded that the systematic underestimation error in the platens compression test can be only approximated and is in the range of 20-40%; the substantial random error (+/-12.5%) confounds correction, particularly when the sample size is small. These errors should be considered when interpreting results from the platens test, and more accurate testing techniques should be used when such errors are not acceptable.

Animals↗

PubMed1996

Impact direction from a fall influences the failure load of the proximal femur as much as age-related bone loss.

Recent studies have shown that factors related to fall biomechanics may play as important a role in the etiology of hip fracture as age-related bone loss. Motivated by finite element analyses that showed failure of the proximal femur to be sensitive to loading direction, our objective with the current investigation was to determine experimentally if changes in impact direction affect the failure load of the elderly proximal femur. Thirty-three cadaveric femurs were assigned randomly to three groups of 11 and tested at one of three loading angles, 0 degree, 15 degrees, or 30 degrees, representing a fall on the hip rolled slightly forward, to the side, or rolled slightly backwards, respectively. Femurs were scanned using dual-energy X-ray absorptiometry (DXA) to assess bone mineral density (BMD) and tested to failure in a fall loading configuration at a displacement rate of 100 mm/second. Using an analysis of covariance to adjust for total hip BMD, we found that failure load decreased by 24% as the loading angle changed from 0 degree to 30 degrees. This reduction in failure load is comparable to that associated with about 25 years of age-related bone loss after the age of 65. Therefore, the impact direction associated primarily with a fall is a critical determinant of hip fracture risk that is both independent of bone density and associated with fall biomechanics.

Accidental Falls↗