A mucous cyst is a specific type of finger cyst. It occurs at the last joint of the finger (the dip or distal interphalangeal joint). It is the result of an underlying bone spur that irritates the joint and causes it to produce extra fluid that results in a small cyst under the skin. Because of the location of the cyst, it often causes a groove in the nail.
Treatment often requires a minor surgery. The purpose of the surgery is to remove the small bone spur that is causing all the trouble. Treatment aimed only at the cyst, such as draining it or “freezing it”, can injure the skin and does not solve the problem. Poking the cyst with a needle at home may temporarily relieve the pain from pressure but risks infection.