Joint stiffness is caused by inflammation in the synovium, the lining of the joint and joint pain can be caused by many types of injuries or conditions. No matter what causes it, joint pain and stiffness can be very bothersome. Rheumatoid arthritis is an autoimmune disorder that causes stiffness and pain in the joints. Osteoarthritis involves growth of bone spurs and degeneration of cartilage at a joint. It is very common in adults older than 45 and can cause joint pain.