Per WiseGeek, this is the definition of a spiral fracture:
A spiral fracture is a type of bone fracture which is caused by a twisting force. You may also hear spiral fractures referred to as torsion fractures, in a reference to the forces involved to create a spiral fracture. Because the break is helical, it can be difficult to treat a spiral fracture, involving months in a cast and possible surgery, depending on the location of the break, the general health of the individual, and the specific circumstances involved in a fracture.
I would also add that this type of fracture is common in skiing accidents and ahem, roller blading…
(continued at http://www.bradleyandme.net/?p=1592)
Thanks for reading!