Objetive:

The properties of the materials that constitute the bone tissue are decisive in its mechanical strength but the factors that influence it are partially unknown at present.

Material and method:

In this paper, we gauge bone hardness by means of ultra-microindentation tests with a Berkovich tip and a 150 mN load in femurs of Sprague-Dawley rats subjected to a transverse fracture or a subtraction osteotomy. The results are compared in different bone locations and experimental groups. The study includes the following four experimental groups, each consisting of four rats: a) standard diaphyseal fracture; b) fracture plus osteotomy of 2 mm; c) osteotomy treated with human parathyroid hormone, PTH (1-84); d) osteotomy treated with strontium ranelate.

Results:

We found the hardness of the material was consistently greater in cortical bone than in trabecular bone. It was also consistently higher in the upper femoral epiphyses than in the lower epiphyses (difference of 1.2 standard deviations). The surgery reduced hardness in the operated femur (difference of 0.3 standard deviations, p=5.5 x10-2). PTH treatment induced a slight but consistent increase in hardness at all sites (p=1.8x10-5) while the effect of strontium ranelate was inconsistent.

Conclusions:

These data show that tissue micro-hardness is influenced by a variety of factors, including anatomy, type of bone tissue, skeletal injury and drug therapy. Therefore, future studies on tissue quality should be carefully designed with these factors in mind.

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