Finding of microdamage morphology differences in mouse femoral bones with distinct mineralization levels

Microdamage progression in bone is dependent on the ultrastructure of the tissue. Thus, any pathological changes in bone ultrastructure may be reflected in the pattern and capacity of microdamage accumulation. A previous numerical study of microdamage progression in bone using a probabilistic failure analysis approach predicts that the microdamage morphology (either linear microcracks or diffuse damage) is very sensitive to the level of mineralization in bone, which is also implicated in some experimental observations. To examine the prediction, femurs from two strains of mice (C57BL/6J, N = 10 and C3H/HeJ, N = 11) that have distinct mineralization levels were fatigued under four-point bending to create damage in the bone tissues. After testing, the microdamage morphology of the bone samples was examined using bulk-staining technique with basic fuchsin. The results demonstrate that more linear microcracks are observed in femurs of C3H/HeJ (higher mineralization), whereas more diffuse-like damage is found in C57BL/6J femurs (less mineralized). Compared with linear microcracks, the formation of diffuse damage tends to dissipate more energy and help bone to avoid catastrophic failures. Therefore, results from this study may help explain why highly mineralized bone tends to be more brittle. Observations from this study are consistent with the numerical prediction from the previous study, suggesting that mineralization has a significant effect on the microdamage morphology of bone.