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Investigating human femur failure due to sideways fall
DOI:10.1038/bonekey.2014.51
Twelve cadaver proximal femurs from individuals with an average age of 76 years were tested to assess the biomechanics of an impact caused by a sideways fall. CT-based, nonlinear finite element analysis was employed to incorporate 82 elements (micron-sized) with around 120 elements per model. This enabled the researchers to examine the site of initial structural failure in each femur to estimate where and how the internal tissue had failed during the impact.
Failure of only a very small proportion of bone tissue (1.5% to 6.4%) in the samples tested caused structural femur failure. Simulations revealed that failure of all the femurs started in the trabecular tissue, which was enough to trigger overall failure with very little cortical tissue involvement. The femurs that had the lowest measured strength relative to bone mineral density assessed by dual-energy X-ray absorptiometry, also had the lowest proportion of trabecular bone compared to cortical bone at the femoral neck.
Editor’s comment: This well-designed experimental and computational study uses a nonlinear, voxel-based finite element method to examine the yielding pattern of the proximal femur in a sideways fall. Besides the excellent predictive capability of the finite element method, the authors show convincingly that yielding is initiated in a tiny volume of trabecular bone of the trochanter and/or subcapital region of the femur. Although further work will be necessary to consolidate their findings, these encouraging results will lead to a better understanding of femoral fractures and will have deep implications for their prevention.
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