There are basically three primary distortion between bones. The first and most serious is a dislocation. That is where two bones become completely out of alignment with respect to each other resulting in typically massive soft tissue damage and neurological nightmares. If you have one of these, it is unlikely you are reading this from anywhere but the hospital.
The second distortion is called a SUBLUXATION. A SUBLUXATION is where two vertebra have shifted out of their normal alignment. This causes a stress on the soft tissues resulting in inflammation of the connective tissues. The inflammation stimulates the pain nerve which then causes the muscles to go into a spasm. It also causes a motor deficit. This means that the tissues (muscles, organs, glands) are weaker in their function. The greater the dysfunction, the greater the symptoms.
The third distortion is called a FIXATION. This distortion is where the vertebra are locked on a block unit rather than moving individually. They create similar symptoms as the subluxation.