by Travis L. Turnbull Human cortical bone, like many engineering materials, is subject to damage and fracture, especially resulting from cyclic loading conditions routinely experienced by the load-bearing long bones. Unlike other materials, bone possesses a unique ability to repair damage and prevent or reduce fracture risk. However, in cases such as athletes and military recruits, the rate and extent of damage formation can exceed the rate of repair, thus increasing fracture risk until the damage is diagnosed and rest prescribed. Another example of an imbalance in bone repair processes occurs in the elderly, and is especially prevalent in those with bone diseases such as osteoporosis. The body consumes calcium stored in the bones with aging and, especially in the case of osteoporosis, the rate of bone resorption exceeds the rate of formation of new bone. Consequently, bone thickness is reduced and porosity—void spaces resulting from the removal without subsequent formation of new bone—increases, thus increasing fracture risk.