Computational Strength Determination of Human Long Bones

With the increased number of airbags and other advanced restraint systems, the upper and lower extremities are becoming more widely studied to determine the injury potential from these devices. However, little injury tolerance data exist for whole bones. To address this deficiency, a finite element model of a female upper extremity was created from computed tomography scan data. A constant density of 1.86 g/cm³ was assumed with a previously developed transversely isotropic, elastic- plastic material model that incorporates rate effects through a modification to the longitudinal modulus and yield stress. Qualitative simulations were conducted for tension, compression, and torsion along the long axis of the bone and for three-point bending in the anterior-posterior direction. Failure was shown to occur in the area of weakest strength or greatest load. While some agreement was made with the expected fracture patterns, a greater mesh density is needed to achieve a better prediction of fracture propagation. A calculated quasi-static ultimate failure moment of 31.0 N-m for the radius and 30.8 N-m for the ulna compared favorably with data available in the literature. Dynamic simulations calculated an ultimate failure moment of 100.0 N-m for a supinated forearm and 73.0 N-m for a pronated forearm, both of which agree with previous testing. Using the methods employed here, models of human long bones can be created and used for simulations to predict strength and injury potential where testing might not be practical.