Introduction Study of the variations of bone characteristics with age in different animal models is important to design musculoskeletal studies. Thus, this study aimed to evaluate the bone mass, dimensions, and biomechanical parameters of the femur in young, middle-aged, and aged Wistar rats. Materials and Methods Thirty male rats (Rattus norvegicus) were divided in three groups (n = 10 per group)—3-month-old young rats, 12-month-old middle-aged rats, and 18-months-old aged rats. The right femurs were subjected sequentially to morphometric study (bone weight, cortical thickness) and biomechanical tests (maximum resistance strength and bone stiffness). Results We observed a significant increase in femur histological (cortical thickness) and biomechanical (maximum strength and bone stiffness) parameters with aging when compared with young animals. Conclusions With the advancing age, the right femoral bone of middle-aged and old animals had greater variations when compared with young animals. However, further studies with the aid of a comparison between right and left femur and other long bones in both male and female rats are needed to corroborate with our findings.

Introduction: previous studies of variation in bone dimensions and biomechanical characteristics with age have involved comparison of young and adult rats, but no data on age-related changes are available. Such data are important for studies of the response of bone to experimental stimuli in aged rats, to distinguish the response to the stimuli from accompanying age-related changes. The present study evaluates the bone mass, dimensions and biomechanical parameters of the femur in young, middle-aged, and aged rats. Thirty-six Wistar male rats were studied: 12 young animals, (3-month-old), 12 middle-aged animals (12-month-old) and 12 aged rats (18-month-old). The right femurs were subjected sequentially to morphometric study (bone weight, cortical thickness) and biomechanical tests (maximum resistance strength and bone stiffness). The statistical differences between groups of animals were tested using the nonparametric Mann-Whitney test (p<0.05). The body weight increased from 274 g to 412.80 g and to 390 g in the groups; the bone weight increased from 0.596 g to 0.823 g and to 0.809 g in the groups; the cortical thickness increased from 380.20 µm to 477.5 µm and to 485.80 µm; the maximum resistance strength increased from 72.59 N to 131.5 N and to 132.4 N and the bone stiffness increased from 79.99 kN/m to 189.0 kN/m to 161.60 kN/m. The differences between the 3-month-old and the two other groups were statistically significant (p<0.05). The body weight increased 50% from 3 to 12 months and 42.3% from 3 to 18 months; the cortical thickness increased 25.6% from 3 to 12 months and 21.7 % from 3 to 18 months; the maximum resistance strength increased 81.1% from 3 to 12 months and 82.31 % from 3 to 18 months; the bone stiffness increased 136% from 3 to 12 months and 102.02 % from 3 to 18 months. In conclusion, for the femoral bone of the Wistar rat, the cortical thickness, the maximum resistance strength and the bone stiffness increased from 3 to 12 mo, but not from 12-to 18-mo-old.