Laboratory Studies
No specific laboratory studies are necessary when a diagnosis of lumbar facet arthropathy is being considered.
Imaging Studies
Abnormalities on plain radiographs, computed tomography (CT) scans, and magnetic resonance imaging (MRI) scans [14] are not specific for patients with back pain; degenerative changes are often found in asymptomatic persons. Although some clinicians may use plain radiography and CT scanning to investigate or even diagnose facet joint pain, no radiographic findings identify lumbar facet joints as the source of low back pain and referred lower extremity pain. [48]
A limited number of studies have attempted to establish correlation between osteoarthritic changes and response to blocking of the joints. While some earlier studies demonstrated such a relationship, others have failed to do so. Furthermore, findings from MRI scans, CT scans, dynamic bending radiographs, and radionuclide bone scans cannot be used to reliably help predict lumbar facet joint pain.
Schwarzer and colleagues concluded that CT scanning has no place in the diagnosis of lumbar facet joint pain. [49] They used the stringent criteria of 80% pain relief for the duration of bupivacaine anesthesia and negative relief with saline control injection. The investigators did not observe any correlation between CT-scan findings and response to diagnostic injections.
Procedures
The use of diagnostic blocks is fundamental to a diagnosis of lumbar facet joint pain. Regardless of the symptoms, one characteristic that all patients with such pain share is the relief of pain once a local anesthetic has been injected. Fluoroscopically guided blocks of the joints constitute the only available standard to correlate with any clinical or radiographic test for facet joint pain. [13]
Single diagnostic blocks are a poor standard. Those employed without the provision of controls led to a false-positive rate of 38% in a lumbar study [29] and a 27% false-positive rate in a cervical study, with a 32% placebo rate in still another investigation. If an investigator relied on a single, uncontrolled block, 1 of every 3 apparently positive blocks would be a false positive. A reliable diagnosis must be accompanied by observation in relation to control subjects.
Control observation can be achieved either with saline injection around the joint while shielding the patient from view of the injections or through use of a confirmatory block. In a confirmatory block, relief achieved with the first local anesthetic is accompanied by relief provided by a second injection for a duration commensurate with the half-life of the second local anesthetic. A patient with genuine facet joint pain should experience relief with the first injection and feel no relief if injected with saline or, if injected with the confirmatory block, experience the same relief that he/she did with the first injection, but for a longer period of time.
The use of double blocks to confirm facet pain is not without limitations. When an appropriate duration of relief with a confirmatory block was required, Lord and colleagues found in cervical studies that specificity was high (88%) but that sensitivity was low (54%) in comparison with double-blinded, randomized, placebo-controlled triple blocks. [50] When diagnostic criteria for the double blocks were expanded to include all patients with reproducible relief, regardless of duration, sensitivity increased to 100% but specificity was lowered to 65%. The authors concluded that a clinician's choice of controls depends on the implications of the results. If innocuous therapy is prescribed, relief of pain, regardless of duration, with a double block may suffice. When diagnostic certainty is critical, such as in a medicolegal context or when surgical intervention is contemplated, placebo-controlled blocks are recommended.
The use of saline around the joint for control observation also has limitations. Of the various possible combinations of responses to 2 injections, pain relief in the same patient with local anesthetic and with saline poses a dilemma. The clinician could conclude that the patient does not have facet joint pain, having falsely responded to the local anesthetic and to the saline. However, a response to the saline injection does not necessarily negate the validity of the first injection with local anesthetic; it may instead indicate that the patient responded to a placebo. The individual may have true facet pain in addition to being a placebo responder. Because of this, some clinicians often proceed with RF neurotomy in patients who obtain 80% relief with lidocaine and with saline, depending on the clinical presentation. Studies are being conducted to report outcomes based on such an approach.
Facet diagnostic blocks can be performed intra-articularly and at the dorsal medial branches that supply the joint. The latter site is used if the joint is not accessible or as a means of avoiding the theoretical risk of needle damage to the joint. Barnsley and Bogduk found that local anesthetic blocks of the cervical medial branches are a specific test for the diagnosis of cervical facet joint pain. In their study, local anesthetic always reached the target nerve and did not affect any other diagnostically important structures. [51] Dreyfuss and colleagues determined that, with the use of appropriate technique, lumbar medial branch blocks are target specific. [52] The use of 0.5 mL of lidocaine adequately bathed the site of the target nerve and trivialized the spread to the dorsal root or the epidural spread to other potential pain generators.
With well-controlled studies reporting 7-14% prevalence rates for facet joint pain, clinicians must adopt stringent criteria for diagnosing facet joint pain. In this way, they can avoid unnecessarily subjecting a large portion of patients with chronic low back pain to various treatments aimed at facet joint pain.
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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).
