What It Is
The facet joints are the connections between the bones of the spine. The nerve roots pass through these joints to go from the spinal cord to the arms, legs and other parts of the body.
These joints also allow the spine to bend and twist, and they keep the back from slipping too far forward or twisting without limits. Like the knee joint, they have cartilage to allow smooth movement where two bones meet. The joints are lined with the synovium and have lubricating joint fluid.
When these joints get swollen and painful because of injury or arthritis, it causes pain. If the affected joint is in the neck, it may cause headaches and difficulty moving the head. If it is in the back, it may cause pain in the lower back, buttocks or thighs.