A tendon is a tough band of connective tissue that joins muscle to bone. Tendons and joints have a masking of membrane that produces a lubricating fluid to help their function. A ganglion cyst is a benign (non-cancerous) ball of fluid that grows on the membrane or sheath that covers these tendons and joints. The backs of the arms and wrists are most generally affected, but ganglion cysts can vary so often develop at the feet, knees and ankles. A ganglion cyst is the maximum not unusual lump at the hand, and has a tendency to goal women among a while of 20 and forty years of age, for reasons unknown.