P Naick | PubMed Health

PubMed1998

En bloc staining of bone under load does not improve dye diffusion into microcracks.

Microdamage accumulation in bone has been implicated in the pathogenesis of some bone fractures, and in implant loosening. Standard techniques for staining microcracks may not allow all cracks to be stained. We tested the hypothesis that crack closure in bone cortices after removal of a bending load may prevent diffusion of stain to sites of microcrack nucleation. Following cyclic loading, 26 canine femurs were divided into a group stained en bloc while applying a four point bending load, and another group stained without an applied load. No differences in number or length of microcracks were observed, indicating that crack closure does not prevent diffusion of stain to the crack location. Staining under load is unnecessary.

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PubMed1998

Does microdamage accumulation affect the mechanical properties of bone?

It has never been demonstrated that microcrack accumulation in bone leads to impaired mechanical properties. We hypothesized that microdamage accumulation is positively and linearly correlated with a reduction in bone's elastic modulus. We also tested the hypothesis that damage accumulates more rapidly in tensile cortices, but crack growth is greater in compressive cortices. Canine femurs (n = 26) were tested in four-point cyclic bending under load control until they had lost between 5 and 43% of their stiffness. Ten femurs were used as nonloaded controls. The loaded portion of the bone was stained en bloc with basic fuchsin to detect the presence of microdamage. The number of stained microcracks, their lengths and the area of damaged bone were measured under the microscope. Crack numerical density, surface density, mean crack length, and the percentage of damaged area were calculated. Significant microdamage accumulation was not detected until the bone had lost 15% of its elastic modulus. The relationship between crack density and stiffness loss was approximately quadratic, but the relationship between damaged area and stiffness loss was linear. There were significantly more microcracks in tensile cortices, but on average cracks were significantly longer in compressive cortices. We conclude that microcrack accumulation impairs the mechanical properties of bone by reducing its elastic modulus. We also conclude that damage accumulates more rapidly in tensile cortices, but crack growth is greater in compressive cortices.

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