Effect of age on femur whole-bone bending strength of mature rat

Skeletally mature rodents are frequently used in studies of bone health and bone healing, some of them requiring longitudinal observations that span a significant portion of the animals' adulthood. However, changes in whole bone mechanics associated with the natural aging of adult rats have not been extensively characterized.

Femurs from skeletally mature Wistar rats in three age groups of 24-week (young adult), 39-week (middle-age), and 54-week (late middle-age) were tested under three-point bending load in the anterior-posterior direction. Mechanical properties and geometric properties of the femurs from the two older groups were compared to the 24-week rats.

Significantly greater strength, rigidity, and post-yield deformation were found in the 54-week group when compared to the 24-week group. The oldest group also demonstrated greater leg length, anteroposterior width, and cross-sectional moment of inertia over the youngest group. Of the intrinsic properties, the highest ultimate stress was found in the 39-week and was significantly higher than the 24-week group. The ultimate strain increased with age, and the difference between the youngest and the oldest group was statistically significant.

The results suggest that femoral bending properties and geometric properties are continually modified from young adult to late-middle-aged animals. Knowing the baseline bone strength and rigidity throughout adulthood of a rodent breed helps guide animal selection in study design.