Mucous cysts are small, fluid-filled sacs that form on the fingers. They are associated with osteoarthritis (OA) and usually develop in patients fifty to seventy years old. These cysts appear between the last joint of the finger and the bottom of the fingernail. Unless a mucous cyst is painful or in danger or rupturing, it can be left alone without causing  harm to the patient. But even surgically removing a mucous cyst may not alleviate pain if the underlying cause of the pain is OA.