text: 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.\n\nJoint pain may also be caused by bursitis (inflammation of the bursae). The bursae are fluid-filled sacs that cushion and pad bony prominences, allowing muscles and tendons to move freely over the bone.\n\nCommon Causes  \n\nUnusual exertion or overuse, including strains or sprains \nInjury, including fracture \nGout (especially found in the big toe) \nOsteoarthritis \nSeptic arthritis \nTendonitis \nBursitis \nInfectious diseases, including \nInfluenza \nMeasles (rubeola) \nRheumatic fever \nEpstein-Barr viral syndrome \nHepatitis \nMumps \nRubella (German measles) \nVaricella (chickenpox) \nChondromalacia patellae \nOsteomyelitis \nAutoimmune diseases such as rheumatoid arthritis and lupus