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The Art of Cortical Bone Dynamic Fracture

Leslie Lamberson (Drexel)

Dynamic Behavior of Materials

Tue 10:45 - 12:15

Salomon 101

Stress fractures remain one of the most common overuse injuries in dancers and athletes. The site of crack initiation in cortical bone is important – if located on the compression side of the bone, it is more stable, but on the tension side of the bone, it has a high risk for separation leading to complete fracture. For women dancing 'en pointe,' metatarsal stress fractures and full fractures are common due to the increased stress forces transmitted. Early diagnosis improves the outcome of conservative treatment of the stress fracture, however little is understood regarding the mechanical relationship between this unique loading signature (dynamic fatiguing) and crack initiation and propagation in cortical bone under impact type loading conditions. In addition, current experimental techniques such as Kolsky bar or indentation tests used to determine the constitutive material behavior in dynamic response predictions do not take into account a history or evolution of micromechanical structural damage that may have occurred prior to the catastrophic fracture event. This mechanistic history of the bone may drastically affect the conditions under which cortical bone transitions from microscale damage to macroscale crack initiation and propagation. As such, this talk presents characteristic impulsive loading signatures experienced by professional ballet dancers and collegiate basketball players. These signatures are then recreated in the laboratory on dry ox and feline inferior bones using a gas-gun impactor and unique sample gimbal mount at intermediate strain-rates. Preliminary results suggest that not only the preconditioning from dynamic fatiguing, but the orientation of the load on the bone affect its crack growth energetics, highlighting the highly anisotropic nature of the material.