Osteoarthritis is a common cause of bumps on the finger joints. The joints most commonly affected are the joint at the base of the thumb, the joints in the middle of the fingers and those at the base of the nails, the Arthritis Foundation explains.
Rheumatoid arthritis, a chronic inflammatory disease that affects the lining of the joints, also frequently affects the fingers, causing deformities of the joints, the Arthritis Foundation reports. Another common cause of joint bumps are ganglion cysts. These most often occur on the joints at the base of the fingers, those closest to the nail and on the wrist. Gout, a form of arthritis that occurs when excess amounts of uric acid accumulate in the blood, usually first affects the joint in the big toe. However, subsequent attacks often cause swelling in the fingers and lumps, called tophi, under the skin of the hands.