3D characterization of bone strains in the rat tibia loading model.

Bone strain is considered one of the factors inducing bone tissue response to loading. Nevertheless, where animal studies can provide detailed data on bone response, they only offer limited information on experimental bone strains. Including micro-CT-based finite element (micro FE) models in the analysis represents a potent methodology for quantifying strains in bone. Therefore, the main objective of this study was to develop and validate specimen-specific micro FE models for the assessment of bone strains in the rat tibia compression model. Eight rat limbs were subjected to axial compression loading; strain at the medio-proximal site of the tibiae was measured by means of strain gauges. Specimen-specific micro FE models were created and analyzed. Repeated measurements on each limb indicated that the effect of limb positioning was small (COV = 6.45 ± 2.27 %). Instead, the difference in the measured strains between the animals was high (54.2%). The computational strains calculated at the strain gauge site highly correlated to the measured strains (R (2) = 0.95). Maximum peak strains calculated at exactly 25% of the tibia length for all specimens were equal to 435.11 ± 77.88 microstrains (COV = 17.19%). In conclusion, we showed that strain gauge measurements are very sensitive to the exact strain gauge location on the bone; hence, the use of strain gauge data only is not recommended for studies that address at identifying reliable relationships between tissue response and local strains. Instead, specimen-specific micro FE models of rat tibiae provide accurate estimates of tissue-level strains.