X-rays are a diagnostic tool used to determine whether an injured individual has a fractured bone.
When an individual goes to the hospital an x-ray is usually done as a precautionary measure. This is to make sure that there has not been a fracture to a vertebrae. The x-ray is a limited diagnostic tool though, because it does not show soft tissue damage.
When an individual injures their shoulder, back, or knee they are told that the x-ray is negative. This certainly does not mean that the person was not injured because x-rays do not show soft tissue, disc damage, ligament or tendon damage. This is because we are not dealing with injuries to the bone and soft tissues.
While an x-ray is an important diagnostic tool, it certainly should not be the only diagnostic tool used to determine whether or not someone has sustained a serious injury.