The facet joints are small joints about the size of the larger knuckle on your index finger. They have cartilage, fluid, a capsule, and all of the components of any other joint in the body. They can be damaged and develop arthritis, or they can be involved with other forms of arthritis. They can be out of alignment (subluxed). When they are painful the pain is usually felt in the back, but may also be felt in the upper leg down to the knee.