Radiologic imaging of facet joints Faure M (1) Huyskens J (1) Van Goethem JWM (1) Venstermans C (1) Van Den Hauwe L (1) De Belder F (1) Parizel PM (1) (1) Antwerp University Hospital & University of Antwerp Department of Radiology Wilrijkstraat 10 2650 Edegem Belgium Radiologic imaging of facet joints Faure M, Huyskens J, Van Goethem JWM, Venstermans C, Van Den Hauwe L, De Belder F, Parizel PM; Antwerp University Hospital & University of Antwerp, Belgium 1. Table of contents Radiologic imaging of facet Joints ...................................................................................................................... 1 1 Table of contents .................................................................................................................................... 2 2 Introduction.............................................................................................................................................. 2 3 Facet Joint disease ................................................................................................................................. 3 4 Radiography ............................................................................................................................................. 4 5 Computed Tomography....................................................................................................................... 4 6 Magnetic Resonance imaging............................................................................................................ 5 7 SPECT-CT................................................................................................................................................... 5 8. Conclusion................................................................................................................................................. 6 9. Figures and tables ................................................................................................................................. 6 10. References...............................................................................................................................................11 2. Introduction Low back pain has a high prevalence and has substantial socioeconomic implications. Imaging is frequently used to examine patients with aspecific back pain with or without irradiating pain. The correlation between anatomic abnormalities seen on imaging, clinical history and outcome remains controversial. In some cases the source of back pain cannot be determined with certainty on imaging studies. The diagnosis and treatment of back pain remains problematic due to the large number and diversity of potential pain generators in the lumbar spine. Most literature focuses on the intervertebral discs, however it is increasingly apparent that the zygapophysial Joint aka “facet” Joints also play a maJor role in low back pain. Diagnosis of facet-mediated spinal pain is difficult. History and physical examination may suggest, but cannot confirm, the facet Joint as the source of pain (Hancock et al. 2007). Although radiologists are commonly asked by clinicians to determine the degree of facet joint osteoarthritis, the published radiological investigations report no correlation between the clinical symptoms of low back pain and degenerative spinal changes observed on radiologic imaging studies (Schwarzer et al. 1995). Specifically, the association between degenerative changes in the lumbar facet Joints and symptomatic low back pain remains unclear and is a subJect of ongoing debate. Facet Joint osteoarthritis is intimately linked to the distinct but functionally related condition of degenerative disc disease (figure 1), which affect structures in the anterior aspect of the vertebral column (Gellhorn et al 2012). 3. Facet joint disease The facet joints are the articulations of the posterior arch of the vertebrae. They are an important part of the posterior column and provide structural stability to the vertebral column. These Joints are surrounded with a fibrous capsule and connect the superior and interior articular facets of the vertebrae. The posterior ligamentous complex (facet Joint capsule, ligamentum flavum, interspinous ligament and suprapinous ligament) keeps the facet Joints and the vertebrae in a fixed position with each other. InJury of this complex can result in subluxation or dislocation of the facet. The facet Joints are composed of two articular surfaces. Unlike the intervertebral disc, they are true synovial joints. The Joint produces synovial fluid, the prime lubricant for the joint and the nutritional source for the joint surface cartilage. Like in all synovial lined Joints, arthrosis is a continuum between loss of joint space narrowing, loss of synovial fluid and cartilage and bony overgrowth. High grade cartilage necrosis arises quite rapidly in facets. Facet arthrosis or degenerative facet disease is the most frequent form of facet pathology. It is mainly a disease affecting the elderly population, present in virtually everyone after the each of 60 and in varying degrees affecting the maJority of adults, suggesting that facet arthrosis has a maJor role in neck pain and back pain in the elderly population. Degenerative facet disease in many cases already begins before the age of 20. There is no gender preference. It is probably related to mechanical loading, minor repetitive trauma and/or a form of predisposition. Symptoms and signs are very aspecific and can be variably progressive. Most commonly it gives rise to a mechanical type of neck or back pain, but it can also be asyptomatic. Studies have shown that facet Joints are clinically important spinal pain generators and patients with symptomatic facet Joints can benefit from specific interventions . The symptoms are frequently aggrevated by extension and alleviated by flexion, with pain not irradiating below the knee. There is a poor correlation between pain and the extent of degeneration. Mechanical stress is exacerbated in facets that are more horizontal in a sagittal plane, typically at the L4-L5 level (figure 2). In imaging studies more and more the emphasis lies on the visualization of inflammation of the facet Joint and the surrounding soft tissues. It is believed that this inflammation is the cause of local, i.e. non-irradiating, pain. Not all changes are inflammatory, especially bony overgrowth is a protective reaction to inflammation, diminishing inflammatory response. However bony overgrowth can be an important cause of neuroforaminal narrowing, giving rise to irradiating pain. Degenerative spondylolisthesis is a displacement of one vertebra relative to another in the sagittal plane. In many cases it is related to facet Joint arthrosis and failure of the motion segment. Listhesis occurs as a result of subluxation of the facet Joint, related to important and progressive loss of cartilage and articular remodeling (figure 2). A more sagittal Joint orientation might lessen the amount of anterior restraint that the facet Joints are able to supply to the vertebral column simply because there is less of a bony barrier in the sagittal plane. This lack of restraint can result in anterior slippage of the superior vertebra in the motion segment. Spondylolisthesis therefore most often occurs at L4–L5, the same level that is most often affected by arthrosis. This can narrow the spinal canal and the neuroforamina (Gellhorn et al. 2012). Septic facet arthritis or pyogenic facet arthritis is a completely different and rare entity. It can give rise to similar imaging findings as degenerative disease, usually with more inflammation and a more aggressive course. The isolated form should always arise suspicion of tuberculosis or an iatrogenic cause (figure 3). In some cases it is secondary to infection of the discs and/or vertebrae (spondylodiscitis). 4. Radiography Osteoarthritis of the facet joints is a frequent radiographic finding, particularly among the elderly. Standard frontal and lateral radiographs are of limited value. Oblique radiographs are the best proJections to demonstrate the facet Joints of the lower lumbar spine because of their oblique position and curved configuration. Even on oblique views, however, only the portion of each joint that is oriented parallel to the X-ray beam is clearly visible. Degeneration is characterized by Joint space narrowing, sclerosis, bone hypertrophy and osteophytes. Intraarticular gas (“vacuum phenomenon”) (figure 4) may be present and spondylolisthesis is not uncommon. Conventional radiography is insensitive in the detection of mild facet Joint disease and becomes slightly more sensitive for detecting severe disease. Also, with this technique the degree of involvement tends to be underestimated. Therefore, standard radiographs can best be used for screening for facet joint osteoarthritis and grading spondylolisthesis according to the Meyerding classification (table 1) (Meyerding HW. 1932). It is particulary useful for evaluating motion related abnormalities in flexion or extension. This can be very important for assessing instability in case of spondylolisthesis. As mentioned before, the clinical relevance of detecting osteoarthritis of the facet Joints remains unclear and controversial (Pathria M, Sartoris DJ, Resnick D. 1987, Weishaupt D et al. 1999). 5. Computed tomography (CT) In comparison with standard radiographs, CT improves delineation of the facet joints due to its capability to image the Joint in multiple planes and the high contrast between bony structures and