Osteoarthritis is the most common form of arthritis that affects the joints, especially in those over 45 years old. It involves the breakdown of cartilage in the joints which leads to pain, stiffness, and reduced mobility. Risk factors include age, genetics, joint injuries, and obesity. Symptoms may include joint pain, stiffness, swelling, and grinding sensations. Diagnosis involves physical exams, x-rays showing cartilage loss and bone spurs, and ruling out other causes. Treatment focuses on reducing pain and inflammation with medications and physical therapy, as well as weight loss and joint protection. For severe cases, surgical options like joint replacement may be considered.