[The effect of bone marrow ablation on regional biomechanical properties of rat tibia]

Regional (metaphyseal-diaphyseal) biomechanical properties of normal rat tibia, and changes on these biomechanical properties after bone marrow ablation, a model of fracture healing, were examined.

The study included 24 Sprague-Dawley rats that underwent tibial marrow ablation, and eight control rats with no surgical procedure. Proximal metaphyseal, proximal diaphyseal, distal diaphyseal, and distal metaphyseal samples were prepared from the tibias of all rats. In the control group, stiffness (elastic modulus, E), strength (maximum strength, Smax), and toughness (total energy absorption, U) parameters of the regional tibial segments were evaluated under compression loads. In the experimental group, compression was applied following bone marrow ablation on days 1, 3, 7, 9, and 15, and ablation-induced changes in the regional biomechanical properties were studied.

The lowest E, Smax, and U values were obtained from the proximal metaphysis. The highest E and Smax values were from the distal diaphyseal, and the highest U values were from the proximal diaphyseal regions. In ablation-induced rats, decreases were observed in all the mechanical test values during days 1 to 7, followed by slight increases on days 7 to 9, and eventual decreases on days 9 to 15. There were significant differences between the two groups with respect to biomechanical parameters (p<0.05), but no significant differences were found between the tibial regions (p>0.05).

Biomechanically, the most resistant and the weakest anatomic regions of normal rat tibia are the diaphyseal region and proximal metaphysis, respectively. The metabolic changes occurring after bone marrow ablation lead to changes in the mechanical properties of the tibia. The most affected tibial segments from ablation-induced intramedullary injury are the metaphyseal segments.