Ganglions are small sacs (cysts) filled with clear, jellylike fluid. They often appear as bumps on the hands and wrists, but they can also develop on the feet, ankles, knees, or shoulders. A ganglion can grow out of a joint capsule, which surrounds and protects the joint, or out of a tendon sheath, which covers the tendon (the ropelike fibers connecting muscle to bone). Most people with ganglions notice that the bumps appear suddenly.