Femoral neck strength of mouse in two loading configurations: method evaluation and fracture characteristics

We evaluated the mechanical strength of murine femoral neck in two loading configurations. The mechanical strength of the left femora of 25 male mice (weight 39 +/- 4 g) were measured in an axial configuration simulating one-legged stance in a human, and the right femora were tested in a configuration simulating a fall to the lateral side, on the trochanter. The reproducibility of the mechanical testing was 1.6% in the axial configuration and 3.7% in the fall configuration. The femoral neck was slightly stronger in the fall configuration. Typically, a load in the fall direction associated with a basicervical fracture, while axial loading resulted in both mid- and basicervical fractures. The linear bivariate correlation coefficient between the mechanical strengths in the two loading configurations was 0.83. Total bone mineral content (BMC), cortical bone mineral content (CtBMC), volumetric cortical bone mineral density (vCtBMD), and cross-sectional cortical area (CSA), measured at the femoral neck by peripheral quantitative computed tomography (pQCT), had a significant relationship with the femoral neck strength in the axial configuration. The coefficient of variation of the pQCT measurements was 9.1, 5.5, 2.3 and 5.5% for BMC, CtBMC, vCtBMD and CSA, respectively. We conclude that the precision of pQCT is moderate in evaluating the femoral neck of the mouse, and vCtBMD is the most reproducible parameter. The mechanical strength of the murine femoral neck can be measured with high precision by the two mechanical testing configurations presented here.