Facet joints are pairs of small joints in between the vertebrae in the back of the spine. These joints have opposing surfaces of cartilage, which limits friction between the bones. The joint is surrounded by a capsule filled with a small amount of synovial fluid. The synovial fluid acts as an additional lubricant to reduce friction between bones that rub together.
Healthy facet joints support the spine while also allowing a wide range of twisting and bending motion. These joints may become inflamed and painful due to a variety of conditions, such as osteoarthritis, degenerated discs, spinal stenosis, or from a trauma such as a car accident.