Anisotropie Contraction of Cortical Bone Caused by Dehydration of Samples of the Bovine Femur in Vitro

Abstract

Cortical bone from the bovinefemur has been studied to determine any changes in dimensions that might be caused by dehydration and subsequent rehydration of the samples. Nine control and ten embalmed axially oriented parallelepiped samples were produced with nominal dimensions of 5 x 5 x 30 mm. Sequences of oven drying and rehydration were studied, before dehydration in a vacuum desiccator prior to determining ash weights. Vacuum dehydration caused anisotropic shrinkage with statistically different ( p < 0.000 I S ) mean strains of 9200, 27000 and 40 200 microstrain in the axial, circumferential and radial directions respectively. The corresponding mean strains for the embalmed samples were 7200, 21 400 and 34 000 microstrain ( p < 0.000 15). These strains are notably greater than the typically quoted 3000 microstrain peak associated with normal physiological activities. Rehydration of either the control or embalmed samples in isotonic saline did not reproduce the original radial or circumferential dimensions. Due to the small range of ash weights from 69.8 to 75.2 per cent, no meaningfiul correlation between ash weight and shrinkage could be extracted from the data. These findings have a potentially dramatic impact upon the design and conduct of all in vitro studies that use bone, whether fresh or embalmed.

Effects of dehydration-induced structural and material changes on the apparent modulus of cancellous bone

“…The current study has treated the structural changes as isotropic; however, dehydration-induced shrinkage in bone has been shown to be anisotropic at the macroscopic [13] and at the microstructural level [33]. This anisotropy will result in architectural changes that cannot be captured using the methodology described herein.…”

“…Nanoindentation studies performed at the microstructural level report increased elastic modulus and hardness in dehydrated tissues [27,16]. The structure of the bone also changes when water is removed: the spacing between collagen fibrils decreases [18] and a macroscopic shrinkage of the bone dimensions occurs [13]. If dehydrated bone is to be studied, then both of these effects must be considered; however, there are no guidelines for assessing the relative contributions of structural and material changes.…”

Specimen size effect in the volumetric shrinkage of cancellous bone measured at two levels of dehydration

“…The volumetric tissue AIR shrinkage values for cancellous bone are higher than the value of 6% reported in the literature for bovine cortical bone (Finlay and Hardie, 1994;Lees et al, 1984). While the smaller shrinkage observed in cortical bone may be partly attributed to the different measurement methods, it also reflects the greater density of that tissue.…”

“…The experimental techniques employed in this study could be used to quantify the magnitude of residual porosity in more mineralized vs. less mineralized tissues. Combining macroscopic (Finlay and Hardie, 1994) and microscopic (Lees et al, 1984) measurements of shrinkage might also provide insight into the ultrastructure of mineralized tissues.…”

“…Volumetric shrinkages of 6-7% have been reported for bovine cortical bone (Lees et al, 1984;Finlay and Hardie, 1994). More generally, Lees et al (1984) found that the shrinkage of mineralized tissues is inversely related to its hydrated density.…”