Numerous studies have demonstrated that the zygapophyseal joints, particularly in the lumbar spine, are a source of low back pain with or without referred sclerotomal pain.21-23 Several studies also suggest that so-called facet pain may have a higher prevalence than previously suspected, with rates reported as high as 40% in older patients.36-38 While few would dispute the existence of posterior mechanical column pain in the presence of a sagittal deformity (e.g., spondylolisthesis), some investigators have disputed its existence without either such a deformity or coexisting degenerative changes in the motion segment.39
The potential clinical utility of a diagnostic response from anesthetic blockade of a suspected pain generator is highest when there is a significant gap between objective data and subjective complaints.19 Obviously, the ability of the block depends on the pharmacology of the agent used, the anatomical accuracy of the needle placement, and, perhaps most significantly, the ability of the patient to accurately report changes in symptoms. Kaplan et al.40 characterized the ability of lumbar medial branch blocks to anesthetize the facet joint. In this study, 18 asymptomatic individuals were assigned to L4-5 or L5, S1 facet blocks with radiographic contrast until capsular distention elicited pain. No extracapsular contrast extravasations were noted. One week later 15 of the 18 underwent one of two randomized injections with saline or lidocaine. Thirty minutes after medial branch injections, the same individuals underwent repeat capsular distention of the joints that had been distended the preceding week. All five control individuals who received saline injections experienced pain with repeat capsular distention. Only one of the nine patients who received the active block experienced pain on capsular distention. Thus, with strict attention to technique, including the avoidance of inadvertent venous uptake with medial branch injection, facet blockade was successfully accomplished in 89% of the active treatment group.
There are difficulties similar to those discussed for discogenic pain when one is attempting to identify patients who will be candidates for facet block on the basis of physical findings. Several studies to date38,41 have failed to identify predictive value for any clinical findings or feature that would suggest a positive response to facet blockade. Revel et al.41 did note an increased likelihood of response to facet blockade in older patients who were relieved of pain in recumbency and did not have an increase in pain with coughing or use of the Valsalva maneuver. Specificity and sensitivity were increased when range of motion and functional tolerance were included: final sensitivity and specificity were, however, limited at 78 and 80%, respectively.
As is the case with discography, there is no "gold standard" from a surgical point of view that can help to refine the diagnostic accuracy of facet blockade. In the lumbar spine, North et al.42 found that 42% of patients who had greater than 50% relief after facet anesthetic block had clinical improvement 2 years after facet rhizotomy. However, 17% of block responders who did not have facet rhizotomy were improved as well. In the cervical spine, some evidence exists that intervention for a facet-mediated pain problem may be warranted. Several studies43-46 have investigated the reliability of facet blockade in the cervical spine, as well as the utility of radiofrequency (RF) neurotomy.47 There has been one published report investigating the correlation of facet blocks with lumbar fusion,4 but few meaningful conclusions can be drawn from this study, which was retrospective and did not use facet blockade as the definitive diagnostic procedure for surgical decision making.
Thus, at the present time the identification of facet-mediated pain by diagnostic blockade has little meaningful impact on surgical decision making. Based on the literature to date, RF facet rhizotomy may be viable. There are however, no convincing studies in the peer-reviewed literature suggesting that conventional surgical treatment (e.g., arthrodesis) is effective in treating facet-mediated pain syndromes, in the absence of sagittal deformity.
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