A 2012 review 1 concerning facet joint osteoarthritis (FJ OA) explicates the current understanding of the ailment and concurs with the widely-held view that OA represents a failure of the entire facet joint, rather than only the facet joint cartilage.
About Osteoarthritis (OA)
Spinal OA occurs in the facet or zygapophyseal joints—paired joints at the back of the vertebral column— and is closely linked to degenerative disc disease. Though FJ OA has not been as widely studied as knee OA, the most recent view that knee OA is not caused by cartilage degeneration alone but involves a systemic imbalance that inhibits the repair of joint tissues and creates whole-joint failure may also be true of spinal FJ OA.
Facet Joint Osteoarthritis (FJ OA)
FJ OA is the result of a failure in the synovial facet joints, including the surrounding cartilage, ligaments, subchondral bone, synovium, capsule, and periarticular paraspinal soft tissues and muscles. Because the FJ is part of a segmented intervertebral disc, there is an association between degenerative disc disease and FJ OA, which is most often found in the lumbar region of the spine.
Typical cross-sectional imaging (radiograph, CT, and MR) of patients with FJ OA demonstrate narrowing of the space between the facet joints, subarticular bone marrow lesions (BML), erosion, and cysts, enlargement of the articular tissues, formation of osteophytes, and disc degeneration.
The Spine Sections’ Interdependence
Because the facet joint is part of a three-joint motion segment (one disc, two facet joints) of the spine, it is completely distinct from the intervertebral fibrocartilaginous disc articulation. The spine is made up of interconnected motion segments, and joint alignment and load distribution throughout the spinal column are considered integral in the progression of FJ OA.
The three joints in each segment are functionally interdependent. What affects one joint will ultimately affect the others. Injuries or diseases of the disc will cause biochemical or mechanical alterations in the facet joint, and any injury to the posterior structure will affect the disc. Facet joint problems usually start with disc injuries. The three-joint complex may fail due to insult to any of its parts. Because each three-joint segment is connected to another spinal segment, injury to any one section may lead to changes in the segments above or below the injured facet joint.
The discs are usually responsible for bearing loads, and in a healthy spine, the facet joints may carry up to 33 percent of the weight. In cases where the lumbar disc space is severely narrowed, the facet joints may bear up to 70 percent of a spinal load. The muscles around the spine help to stabilize the vertebral column and provide a sense of where the spine is positioned in space. These functions may significantly decrease with age, compromising the motion of the spinal segments and contributing to FJ OA, as well as adult degenerative scoliosis and spondylolisthesis.
Degeneration of the facet joints may begin during youth and progress over many years. Early disruption of the articular cartilage, capsule, and synovium can lead to subchondral bone and bony joint margins in later years. Thinning of the articular cartilage leads to narrowing of the space between the joints, and the cartridge can develop lesions, pitting, fissures, and flaking as it slowly erodes. The joint capsule may receive decreased blood and become fibrous and inflamed. In time, the entire posterior capsule becomes fibrous and inflamed.
Who is at Risk?
Age appears to be a strong correlate the development of FJ OA. Though women are more prone to a diagnosis of FJ OA based upon a lumbar CT, there is no statistically significant difference between genders when it comes to developing FJ OA. Weight—or a high BMI—plays a significant role in the progression of lumbar FJ OA, but it is only slightly relevant as a determinant in the development of cervical FJ OA. African-Americans are less likely than Caucasian Americans to develop FJ OA. Heavy lifting, carrying, or pulling objects has not been studied as a possible correlate, and other occupational motions are most likely not associated with cervical FJ OA. There is a significant correlation between disc-height narrowing and the development of FJ OA in patients of any age, weight, or sex. Patients with disc-height narrowing are twice as likely than disc-height unaffected patients to develop FJ OA. Smoking and other risky habits appear to have little bearing on the development of FJ OA, but there is an apparent correlation between lumbar FJ OA and abdominal aortic calcifications.
Symptoms of FJ OA
FJ OA—alone, or in combination with other disc-related ailments— may cause significant neck or lower back pain (LBP), especially in adults and older patients. This pain can be caused by nociceptors in the bone or surrounding joints. Mechanical pressures on the bone, distension of the surrounding capsules, small fractures, and synovial inflammation can contribute to muscular spasms that sensitize the nerves, creating a chronic cycle of spinal pain.
Diagnosis procedures may include lumbar hyperextension, flexion-straightening, and extension-rotation to determine whether the patient’s pain increases with these exercises. Other types of pain may also indicate FJ OA.
Fat-suppressed MRI spinal sequence studies have shown BML—a common cervical spine finding— in the lumbar FJ articular processes of up to 41 percent of back pain patients. This suggests a link between back pain and FJ BMLs. Many FJ features are easily detectable using fat-suppressed MRI’s. These include FJ effusions and periarticular and ligament edema, though these observations are currently not used to grade or evaluate FJ OA in patients. The role of heredity in the development of FJ OA has not been adequately studied.
FJ OA can contribute to narrowing of the central spinal canal, intervertebral foramina, and the lateral recess, and spinal nerve roots in these areas may be pressed. This situation may be compounded by the development of synovial cysts.
Injury to any part of a spinal motion segment may contribute to whole-joint and/or segment failure, causing neck or back pain. Any change that affects the spinal segments, particularly disc degeneration and unbalanced joint alignment or muscle weakness, may contribute to the development of FJ OA. Aging appears to increase the risk of developing FJ OA.