Finger mucous cyst

Finger mucous cysts are benign growths that usually appear near the last finger joint, often damaged by osteoarthritis of the finger. These cysts form from synovial fluid, a liquid that lubricates the joints. As the joint wears, this fluid can leak out, creating a small pocket under the skin. As it grows, this pocket exerts pressure on the surrounding skin, making it fragile and prone to puncturing, releasing a clear viscous fluid. Sometimes these cysts open spontaneously, increasing the risk of joint infection. If the cyst on a finger presses on the nail matrix, it can cause visible and sometimes painful nail deformity.

The mucoid cyst are closely linked to degenerative processes in the joint, principally osteoarthritis. With age, or as a result of repeated trauma, the joint may wear down and the cartilage deteriorate, leading to the formation of small spaces in the joint. Synovial fluid, normally confined within the joint, may then leak out and form a cyst. Repeated microtrauma to the joint may also contribute to the formation of a mucoid cyst on the finger. Although rarer, this type of cyst can also appear on the toes, in which case it’s known as a toe mucoid cyst.

The main symptom of a finger mucous cyst is the appearance of a small “lump” around the last joint of your fingers, close to the nail. This is often covered by thin, fragile skin, which can break open and leak a clear, viscous liquid. Pressure from the cyst on the nail matrix can also lead to nail deformities, a characteristic symptom of this pathology.

The diagnosis of finger mucous cysts is based primarily on clinical examination. During the consultation, the hand surgeon will assess the size, location and consistency of the cyst. An X-ray is prescribed to assess osteoarthritis of the underlying joint and exclude other pathologies of the hand. This imaging helps confirm osteoarthritis and plan the best possible treatment. In cases where the diagnosis is uncertain, puncture of the cyst may sometimes be considered to analyze the fluid and confirm its mucoid nature.

Treatment of a finger mucous cyst depends on the size of the cyst and the symptoms it causes. Small, asymptomatic and uncomplicated cysts can simply be monitored. If the cyst becomes larger, more painful, or if there is a risk of skin rupture, surgery may be considered. In this case, the cyst is removed in its entirety, along with the weakened skin and joint osteophyte if necessary. The skin defect is filled with a local skin flap or a skin graft taken from the forearm.
If the underlying joint is severely affected by osteoarthritis, another procedure, such as arthrodesis (joint fusion with a screw or staple) may be performed.

It’s important to note that mucoid cyst surgery carries a risk of recurrence, estimated at around 10% of cases, even after successful surgery.

Useful links :

• The British Society for Surgery of the Hand