Non-skeletal determinants of fractures: the potential importance of the mechanics of falls. Study of Osteoporotic Fractures Research Group.

Bones break because the forces applied to them exceed their strength. For most non-spine fractures, this force results from a fall. Falls generate at least 10 times the energy necessary to fracture the proximal femur, but only 5%-10% of falls in older white women cause fractures and only 1% cause hip fractures. The mechanics of the fall plays a very important role in whether a fracture will occur and which bone will fracture. This review postulates that orientation of the fall and location of the impact determine the type of fracture, and whether a fracture occurs depends on the energy of the fall (distance to impact and weight of the moving parts) and how much of that energy is absorbed by protective responses, the impact surface and soft tissues over the bone. Recent case-control studies support the view that the mechanics of a fall are the most important determinant of whether it will result in a hip fracture.