Fractures most often happen when more force is applied to the bone than the bone can take. Bones are weakest when they are twisted.
Bone fractures can be caused by falls, injuries, or direct hits or kicks to the body.
Overuse or repeated motions can tire muscles and put more pressure on a bone. This can cause stress fractures. This is more common in athletes and military recruits.
Fractures can also be caused by diseases that weaken the bone. This includes osteoporosis and cancer in the bones.