History
Little controversy surrounds the facet joint as a possible source of chronic low back pain (LBP). Innervation and possible inflammatory mediators of the joint have been elucidated. Pain upon provocation of the joint, relief upon anesthetization of the same joint in healthy volunteers, and chronic LBP in patients have been documented. Although initially described as a syndrome, investigators now prefer to term it facet joint pain. By definition, a syndrome is a group of signs and symptoms that occur together and characterize a particular abnormality; however, no signs or symptoms have been identified as unique to facet-mediated pain. [39]
A major source of frustration for clinicians has been the fact that no reliable means exist to document a clinical diagnosis of lumbar facet joint pain without the use of invasive techniques. If the true prevalence of facet joint pain was 40-75%, as initially reported, a clinical profile might not be crucial, because all chronic LBP patients would warrant investigation for this disorder. However, a prevalence of 10-15% would indicate that a clinical profile would be important in preventing the indiscriminate use of diagnostic and/or therapeutic blocks.
Biomechanical studies of the facet joint during extension and of facet capsular ligaments strained during rotation initially provided the belief that facet joint pain is worse with extension and rotation. Early studies by Helbig and Lee provided initial credence to this belief, but later studies by Revel and coauthors and by Schwarzer and colleagues did not support it.
Revel's investigation found that an increase in pain during hyperextension and extension-rotation was, in fact, less frequent in the group that responded to the facet joint injection than in the group that did not. [36]
The characteristics of lumbar facet joint pain include the following:
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Location of pain.
Lumbar facet joint pains are lateralized and can radiate below the knee. They rarely, if ever, cause axial or central back pain.
In their study of 26 patients selected by way of differential diagnostic blocks, Schwarzer and colleagues observed that no patients with central pain responded to diagnostic blocks of the facet joints. [29, 30] This study also refuted the commonly held notion that pain below the knee is unlikely to be referred from the facet joint.
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Clinical features of facet joint pain.
In their large 1988 study, Jackson and coauthors could not identify clinically specific facet syndromes or predict with any degree of accuracy which patients were more likely to respond to facet diagnostic blocks. [27] They concluded that facet syndrome is not a reliable clinical diagnosis.
Studies addressing the pattern of referred pain have been unable to distinguish pain from different levels. However, a generally held belief is that facet joint pain is more prevalent among the older population, is more lateralized, and is a more likely diagnosis when radiographic findings show severe facet arthritis.
Physical
See History.
Causes
The cause of most lumbar facet pain is unknown. On occasion, the lumbar facet joints are affected by systemic inflammatory arthritides, such as rheumatoid arthritis and ankylosing spondylitis. The following is a more specific look at sources of low back pain (LBP). [40]
Microtrauma
Microtrauma of the facet joints can produce pain. Small fractures, capsular tears, splits in the articular cartilage, and hemorrhage have been documented on postmortem studies of trauma victims who had normal radiographic findings. Whether these abnormalities were painful was not recorded.
Osteoarthritis
Osteoarthritis is another cause of lumbar facet joint pain. However, not all cases of facet arthritis are painful; the radiographic changes of osteoarthritis are as common in patients with LBP as in those without it. Some studies report that severely degenerated joints are more likely to cause symptoms. In a 2008 report, multidetector computed tomography (CT) scanning in 188 individuals revealed lumbar facet osteoarthritis in 59.6% of males and 66.7% of females. [41] In this study population, however, the report found no association between osteoarthritis at any level of the lumbar spine and the development of LBP.
Reports indicate that the orientation of the facet joints is associated with the development of spinal osteoarthritis. In a study of 150 patients, Linov et al found that a particularly sagittal orientation of the L4 and L5 facet joints appeared to be linked to the disease. [42]
A study by Yoshiiwa et al indicated that ligamentum flavum hypertrophy is related to severe facet joint osteoarthritis, as well as to lumbar segmental instability and severe disk degeneration and a sagittalized facet joint orientation. [43]
Synovial capsule distention and inflammation
Dory attributed LBP from facet syndrome to distention and inflammation of the synovial capsule, with resultant stimulation of the nociceptive nerve endings. [44] Expanded synovial recesses may also compress nerve roots in the spinal canal and neural foramina, which may explain the presence of radicular pain in patients with facet syndrome. Lippitt attributed pain in facet syndrome to a combination of synovitis, segmental instability, and degenerative arthritis. [45]
Rheumatoid arthritis
Using magnetic resonance imaging (MRI) scans, a study by Yamada et al of 201 patients with rheumatoid arthritis found erosion of the lumbar facets and endplates in 76.6% and 70.6% of patients, respectively, with the erosion occurring at 38.7% and 33.8% of intervertebral levels, respectively. Facet and endplate erosion both occurred most commonly at the midlumbar and lower-lumbar areas. A correlation was seen between facet erosion and the presence of spondylolisthesis. [46]
Other
Other theories regarding the causes of LBP include meniscoid entrapment, synovial impingement, joint subluxation, chondromalacia facette, capsular and synovial inflammation, mechanical injury to the joint capsule, and the restriction of normal articular motion from soft or articular causes.
A study by Hawellek et al found a positive correlation between the amount of cartilage calcification in the lumbar facet joints and degeneration of the facet joints and intervertebral disks. The study did not find cartilage calcification in the lumbar facet joints to be associated with patient age, although a correlation was found between age and cartilage calcification in the lumbar intervertebral disks. [47]
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Anteroposterior view of right L4-5 facet intra-articular injection with contrast.
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Lateral view of right L4-5 facet intra-articular injection with contrast.
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Oblique view of right L4-5 facet intra-articular injection with contrast.
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Anteroposterior view of right L5 dorsal medial branch needle position (tip of the needle is at the neck of the sacral ala).
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Lateral view of right L5 dorsal medial branch needle position (tip of the needle is at the neck of the sacral ala, just below the L5-S1 facet joint).
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Anteroposterior view of right L4 dorsal medial branch needle position (tip of the needle is at the neck of the right L5 transverse process).
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Lateral view of right L4 dorsal medial branch needle position (tip of the needle is at the neck of the right L5 transverse process, just below L4-5 facet joint).
