Osteoarthritis is a complex disease that involves the breakdown and eventual loss of articular cartilage in joints. It was formerly considered a simple "wear and tear" process but is now understood to involve inflammation. Symptoms include pain, stiffness, and loss of function in affected joints. Diagnosis is made based on symptoms and confirmed with x-rays showing bone spurs and joint space narrowing. Treatment focuses on reducing pain and inflammation with medications and surgery, including joint replacement, for severe cases.