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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 the surrounding soft tissue. On CT-‐scan we can see articular joint space narrowing with subchondral sclerosis and erosions, osseous overgrowth and/or hypertrophy of the ligamentum flavum, causing impingement of the foramina. Secondary signs include intraarticular gas, joint effusion and spondylolisthesis (figure 2). Synovial cysts can arise, extending posterior of the facet joint, but also anterior in the spinal canal or neuroforamen (figure 5). Joint traction during subluxation may produce intraarticular gas (vacuum). These abnormalities associated with osteoarthritis can be demonstrated and categorized by CT (Carrera GF et al. 1980). Four grades of osteoarthritis of the facet joints were defined by Weishaupt, adapting the criteria published by Pathria: grade 0, normal; grade 1, mild degenerative disease; grade 2, moderate degenerative disease; and grade 3, severe degenerative disease (table 2)(Pathria M, 1987; Weishaupt D, 1998). In the presence of an MR examination CT is not required for the assessment of facet joint degeneration due to relative good interobserver agreement (Weishaupt D et al. 1999). But once again, abnormal morphology may not necessarily reflect underlying pathology.
6. Magnetic Resonance Imaging (MRI)
CT has largely been replaced by MR imaging for the diagnosis of degenerative disc disease, spinal stenosis, infection, and neoplasia of the lumbar spine. MRI is a non-‐invasive investigation that is not associated with exposure to ionizing radiation and provides excellent soft-‐tissue resolution. The role of MR imaging in the evaluation of facet joint degeneration is less clear. Osteoarthritis of these joints may be demonstrated in patients who present with back pain with or without pain irradiating into the legs (Resnick D, Niwayama G. 1995), but is also a frequent observation in a large percentage of asymptomatic patients. As mentioned before CT and MR are consistent in demonstrating morphological aberrances of the facet joint, but MRI is better to demonstrate compression of the thecal sac and the fat-‐filled neuroforamen, compressing the nerve roots (figure 6). MRI also clearly demonstrates the surrounding inflammatory soft tissues (figure 7). (Weishaupt D et al. 1999, Carrino et al. 2008). Recent studies suggest that the facet joint (in contrast to the intervertebral disc), is perhaps better examined in the context of the scientific literature on other synovial joints, unlike the intervertebral disc. Chronic degenerative osteoarthritic processes in these structures involve active synovial inflammation, which can be detected using MRI with a fat-‐saturation technique. Facet synovitis can be graded, using a grading system (table 3). Facet synovitis appears to correlate with the patient’s pain (Czervionke LF and Fenton S. 2008). Moreover synovial abnormalities seem to correlate with SPECT findings (Kim KY, Wang MY. 2006).
7. Single photon emission tomography (SPECT)/CT
As mentioned before the detection of inflammation in the facet joint may be more useful than imaging of joint morphology. Radionuclide bone scintigraphy can depict bone areas with increased osteoblastic activity, and it can depict synovial changes caused by inflammation or hyperemia. Bone scintigraphy also can depict degenerative changes, particularly those that demonstrate a high degree of remodeling. The induced radiopharmaceutical uptake can vary from subtle to pronounced, depending on the metabolic activity and size of the lesions. Osteophytes that are in the process of growing exhibit a high uptake, whereas mature osteophytes tend to have a normal or slightly increased uptake. Abnormalities can be detected sooner with bone scintigraphy than they can be with radiographic methods, and joints observed as abnormal at scintigraphy eventually show the most progressive radiographic changes. Joints that are radiographically abnormal but normal at bone scintigraphy do not show additional deterioration (figure 8). In addition, with SPECT, the sensitivity of the scan for depiction of bone lesions is increased. It appears that patients with positive scans have an excellent response to facet joint injections. In contrast, patients with negative scans and patients who undergo injection without having undergone bone scanning are less likely to have a beneficial response to the injections (Pneumaticos SG. 2006). This means that patients with a negative bone scan could be spared from an invasive procedure such as facet joint injection.
8. Conclusion
CT-‐scan is the most sensitive technique in detecting and grading degenerative facet disease. MRI, on the other hand, is best to demonstrate compression of the thecal sac and the fat-‐filled neuroforamen, compression of the nerve roots, and inflammation of the surrounding soft tissues. Conventional radiography gives us the possibility to see motion related abnormalities in flexion or extension, suggesting instability. Although imaging of joint morphology has not been proven helpful, the detection of inflammation may be more useful. Single photon emission tomography (SPECT) has shown a correlation between radionuclide uptake in the facet joints and response to intra-‐articular injections (Dolan et al. 1996, Pneumaticos et al. 2006). Recent studies showed a correlation between facet joint synovitis seen on MRI and the clinical pain syndrome (Czervionke LF and Fenton S. 2008). Moreover synovial abnormalities on MRI seem to correlate with SPECT findings (Kim KY, Wang MY. 2006).
9. Figures and tables
Table 1: Meyerding classification for spondylolisthesis 1 < 25% displacement of vertebral body 2 25-‐50% displacement of vertebral body 3 50-‐75% displacement of vertebral body 4 >75% displacement of vertebral body 5 Spondyloptosis (Vertebral body displaced completely anteriorly, with inferior
displacement to level of vertebral body below) Table 2: Grade criteria for facet degeneration (Pathria, adapted by Weishaupt) 0 Normal facet joint space (2±4 mm width) 1 Narrowing of the facet joint space (< 2 mm) and/or small
osteophytes and/or mild hypertrophy of the articular process 2 Narrowing of the facet joint space and/or moderate
osteophytes and/or moderate hypertrophy of the articular process and/or mild subarticular bone erosions
3 Narrowing of the facet joint space and/or large osteophytes and/or severe hypertrophy of the articular process and/or severe subarticular bone erosions and/or subchondral cysts
Table 3: Grade criteria facet joint synovitis 0 No signal abnormality 1 Signal abnormality confined to joint capsule 2 Periarticular signal abnormality involving less than 50% of the perimeter of the
joint* 3 Periarticular signal abnormality involving more than 50% of the perimeter of the
joint* 4 Grade 3 with extension of signal abnormality into the intervertebral foramen,
ligamentum flavum, pedicle, transverse process, or vertebral body *Signal abnormality may extend into the articular pillar or lamina, but does not contribute to the definition of the grade.
Figure 1: MRI of the lumbar spine. Sagittal T2 (A) and axial T2 (B) weighted images: a 33-‐year-‐old woman with low back pain: disc degeneration at the L5-‐S1 level with disc protrusion and hypertrophic degenerative facet joints at both sides.
A B Figure 2: CT-‐scan of the lumbar spine. Sagittal (A) and axial (B) reconstructions show degenerative facet joints with an anterolisthesis of L4 due to degeneration of the facet joints. We see hypertrophic bone osteofytes, loss of the articular space and subchondral geode.
A B Figure 3: MRI of the lumbar spine. Sagittal T2-‐ (A), STIR (short TI inversion recovery) (B), T1-‐(C) and CE (contrast enhanced) T1-‐weighted (D) images. Axial T2-‐ (E), T1-‐ and CE T1-‐ weighted images. 58-‐year-‐old woman with erysipelas of the right leg with back pain. Important synovitis of the right facet joint L4-‐L5 with inflammation in the surrounding soft-‐tissue, especially on the fluid sensitive sequence (STIR), with enhancement of the subchondral bone after intravenous gadolinium.
A B C D
E F G Figure 4: Conventional radiography of the lumbar spine. Anteroposterior (A), lateral (B), left (C) and right (D) oblique images. 56-‐year-‐old woman with back pain. Degenerative discs at the L3-‐L4, L4-‐L5 and L5-‐S1 level with associated facet arthrosis, especially at the L2-‐L3 level on the right side, best seen on the right oblique (D).
A B C D Figure 5: MRI of the lumbar spine. Axial T2-‐weighted image showing an intraspinal cyst of the left L4-‐L5 facet joint. Compression of the dural sac and displacements of nerve roots of the cauda equina.
Figure 6: MRI of the lumbar spine. 58-‐year-‐old man with radiculating back pain and claudicatio. Sagittal T2-‐weighted (A), T1-‐weighted (B) and STIR images. Axial T2-‐weighted (D), T1-‐weighted (E) images. Disc degeneration with bulging of the contours and hypertrophic facet arthrosis with spinal stenosis at the L4-‐L5 level and neuroforaminal stenosis at the L3-‐L4, L4-‐L5 and L5-‐S1 level at the left side. Note also subchondral bone edema in the left facet joint L4-‐L5 with intra-‐articular fluid, signs of arthrosynovitis.
A B C
D E Figure 7: MRI of the lumbar spine. 61-‐year-‐old man with radiculating back pain. Sagittal T2-‐ weighted (right A, left B), T1-‐weighted (right C, left D) and STIR (right E, left F) images. Axial T2-‐ (G) and T2-‐ weighted (H) images. Degenerative anterolisthesis of L5 with hypertrophic facet arthrosis at the L3-‐L4, L4-‐L5 and L5-‐S1 level on both sides. Note the radicular compression of the left L5 root (D) due to foraminal stenosis. The axial images clearly show fluid in the degenerative facet joints at the L4-‐L5 level with an arthrosynovial cyst (ganglion) at the left side (G).
A B C D
E F
G H Figure 8: Single photon emission tomography (SPECT) of the lumbar spine. 56-‐year-‐old man with radicular back pain. Bone scintigraphy (A) and axial SPECT-‐CT-‐fused (B and C) and axial CT (D) images at the L2-‐L3 level show increased Technetium uptake in the facet joint on the left side. The other foci of increased uptake where due to disc degeneration.
A B
C D
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