When a bone is subjected to a force that exceeds the ultimate strength of the bone, a fracture occurs. Bone has a unique material property called viscoelasticity. This means that the strength of bone is dependent upon the rate at which it is loaded.
Bone can absorb more energy when loaded rapidly than it can when loaded slowly.
In addition to the magnitude of the force, the direction of the force also influences the type of fracture produced. There are five forces that may act alone or in concert to create fractures. Tension Tension forces are those which tend to produce elongation. Failure occurs along this plane by debonding of bone cement lines and pulling out of osteons. The type of fracture generated is often termed an avulsion fracture.