Biomechanical properties of femoral shafts and bone tissue in protein-malnourished rats from weaning to adulthood

The present study was designed to estimate the bone biomechanical repercussion of protein restriction imposed to rats between the 26th and the 135th days of age. Female rats were placed on either a 4% (P4) or 20% (P20) protein diets. Body weight at the end of the study was 350.5?g (SD?31.0?g) in P20 rats and 87.5?g (19.4?g) in P4 ones. Femur weight and length were significantly reduced. The diaphyseal cross-sectional area and the cross-sectional moment of inertia were also diminished. Femoral calcium concentrations in ashes were similar in both groups. However, the femoral mass (calcium mass) was significantly lower in P4 than in P20 rats. When the femoral bone mass was normalized per 100-g femur, no significant difference between groups was found. The right femur of each animal was subjected to a three-point bending test in order to obtain the load/deformation curve. A significant weakening of bone beams, shown by a correlative impairment of diaphyseal ultimate strength and stiffness, was observed in P4 rats. However, when their values were normalized for body weight, the differences disappeared. The bone material quality indicators, or pre-yield bending stiffness (elastic modulus) and yielding stress were similar in P4 and P20 rats. In summary, we have described a number of alterations in bone morphometrical and biomechanical variables in rat femur shafts resulting from protein restriction from weaning to early adulthood. The clear differences in strength and stiffness of bone beams seemed to be the result of an induced subnormal gain in bone structural properties as a consequence of a correlative subnormal gain in bone growth and mass, yet not in bone material properties.