Aim. The purpose of this study was to examine the symmetry of the mechanical and tomographic properties of the rat femur and tibia, frequently used in biomedical research.

Materials-Methods. For this purpose both femora and tibiae of 43 Wistar rats underwent tomographic (pQCT) evaluation while both femora and tibiae of 40 further Wistar rats were subjected to destructive three-point bending testing. The age of the animals ranged between 3 and 12 months and all were males.

Results. While there was significant variation between the structural and the biomechanical properties between different animals the differences between the femora and the tibiae of the same animal were not statistically significantly different in the majority of animals.

Conclusion. We conclude that in healthy, sexually mature Wistar rats, in the first year of their life, there is no significant diversity in terms of tomographic and biomechanical properties of their opposing posterior limb long bones.

Aim. We evaluated the effect of the intact periosteum on the biomechanical properties of the rat long bones. Materials-Methods. The biomechanical properties of both femora and tibiae of 30 male, 4-month old Wistar rats have been evaluated in three-point bending testing. In one bone of each pair of femora or tibiae the periosteum was preserved intact, while in the contra-lateral bone the periosteum was stripped off. Ultimate strength,stiffness,energy absorption and deflection were derived automatically from the load-deformation curve recorded for each bone.

Results. As regards the femur, the periosteum-covered bones displayed statistically significant higher values for all parameters measured compared to the periosteum-stripped bones. In the tibia, only energy absorption and deflection were significantly higher in the periosteum-covered bones. The fracture pattern was also different in these two groups. The periosteum-stripped femora and tibiae failed catastrophically, while in the periosteum-covered bones the two bone parts remained in close apposition stabilized by the periosteal membrane.

Conclusion. The periosteum exacerbates the biomechanical capacity of intact rat long bones examined in bending, probably taking advantage of its fibrous composition and elastic properties.