An x-ray image of a spiral fracture to the left humerus of a 27-year-old male. The injury was sustained during a fall.
A spiral fracture (a.k.a. torsion fracture) is a bone fracture occurring when torque is applied along the axis of a bone. While torsional forces are being applied along the parallel axis of a bone, planes perpendicular to this axis are not affected. Tension is exerted upon one part of the bone, while compressive forces are exerted upon the other. When these forces have exceeded the limit tolerable by the bone, fracture occurs.