This is called a ruptured disc and it is extremely painful. There are many reasons why cartilage injury occurs, but when it does, the injury progresses to loss of this protective shock absorber. Bone rubs against bone, causing osteoarthritis. OA, one of the oldest and most common types of arthritis, is a disease of the cartilage and leads to injury of the joint. It is not due simply to wear and tear or old age.
Some physicians think of it as the end result of any injury to a joint.
We have no explanation as to where it comes from or what causes it. Several theories about the cause of OA exist. One is that an abnormal release of enzymes from cartilage cells occurs, leading to a breakdown of cartilage and joint destruction. Another theory is that some persons may be born with defective cartilage or with slight abnormalities in the way joints fit together, which may cause cartilage to break down as a person ages. OA is not like RA in that it does not affect symmetrical parts of the body.