A ganglion cyst is a fluid-filled sac which commonly forms in the wrist. The majority of ganglion cysts are benign (not cancerous). They are usually caused by a stretching of the joint capsule under pressure from a weakness in the ligament wall, creating a sac. We call it the “bubble gum effect” – when you blow a bubble, pressure forces air into the stretched out gum and it expands until it pops. Picture bones as your lips, and the ligament (holding two bones together) as the bubble gum. When fluid builds up in the wrist, it can stretch out the ligament in a specific spot and create the cyst. The cysts can be large or small, painful particularly with movement of the wrist. Sometimes they can go away on their own. In the old days, people would take books or bibles and hit the cyst hard in the hopes of popping it.