What are the top reasons for getting artificial joint?

Pain. Pain is the most common reason. Deformity of the joint is second.
Quality of life. Pain, swelling, loss of motion and function, inability to sleep thru the night, inability to do the activities you want to do. Artificial joints restore motion and function allowing you to maintain an active life, which is important for your overall longevity in terms of heart and lung health.
Long lasting pain re. Long lasting pain relief and return to near normal function.