The spinal column is composed of 24 moveable vertebrae that have 63 joints or hinges, and on occasion, joints can get locked into position if a disc bulges or herniates. The discs form a slightly moveable joint, however, the freely moveable joints are the facet joints or the zygapophyseal joints. These joints are where the vertebrae articulate with each other. Collectively the inferior and superior articular processes and the facet joint are called the Zygapophyseal Joints or articular pillars. These joints help carry the axial load of the body and limit the range of motion of the spine. They also make up the back of the intervertebral foramen and may cause stenosis if they hypertrophy in later life.

When discs are displaced, the result is assymetry in the facets joints and either the left or right facet joints become compressed while the other separate. The compressed joints are considered fixated and a release of the joint fixation will result in cavitation, or clicking sound.

The facet joints connect the posterior elements of the vertebral bodies to one another. Like the bones that form other joints in the human body, such as the hip, knee, or elbow, the articular surfaces of the facet joints are covered by a layer of smooth cartilage, surrounded by a strong capsule of ligaments, and lubricated by synovial fluid. Just like the hip and the knee, the facet joints can also become arthritic and painful, and they can be a source of back pain. The pain and discomfort that is caused by degeneration and arthritis of this part of the spine is called facet arthropathy, which simply means a disease or abnormality of the facet joints.

Most people who have facet arthropathy will complain of low back pain that is worse with twisting or extension (bending backwards) of the lumbar spine. The pain is often quite well localized, and unlike the pain and numbness caused by a herniated disc or sciatica, it does not usually radiate into the buttocks or down the legs. However, as the facet joints become arthritic, they often develop bone spurs that can decrease the amount of space available for the nerve roots as they exit the spinal canal. This can be a contributing factor in the development of spinal stenosis, which does cause pain, numbness, and weakness in the buttocks and legs.

Facet arthropathy is rarely the only cause of significant back low back pain, and patients who have this condition often have other disorders that may be contributing to their symptoms, including degenerative disc disease (Spinal Decay), arthritis of other parts of the spine, and often spinal stenosis as well. Most people with even mild to moderate amounts of arthritis of the lumbar spine will have evidence of facet joint degeneration on a CT scan (CAT scan) or MRI. A bone scan, which shows areas of active inflammation in the spine, is a test that can be used to determine whether or not facet arthropathy may be contributing to a patient's back pain.