Osteoarthritis (OA) is a form of arthritis where joint cartilage breaks down. Primary OA has no clear cause. Secondary OA, however, occurs as a result of an existing medical condition, joint injury, or abnormality.
Primary and secondary OA are the same condition, but they have different causes.
OA can affect various joints in the body and may cause pain, stiffness, and limited range of motion.
Source: Medical News Today