Identifying Good Candidates for Lumbar Facet (Medial Branch) Neurotomy:
J. Scott Bainbridge, M.D.
The clinical diagnosis of lumbar zygapophysial joint generated pain, and the differentiation of that entity from other potential sources of low back pain, such as discogenic or sacroiliac joint generated pain, is very important in helping direct appropriate clinical therapies. The specific and efficient use of manual therapy techniques, patient and diagnosis specific exercise regimens, medications, therapeutic Z-joint corticosteroid injections, and/or Z-joint denervation techniques, depends on the accurate clinical diagnosis of Z-joint related pain. The ability to accurately clinically diagnosis this specific cause of low back pain has not been clearly established in the medical literature, although many spine care clinicians believe (through informal discussion or published editorials) that there are clinical features that suggest this diagnosis. Researchers who have tried to correlate various single clinical data points to a response to lumbar Z-joint blockade, have concluded that there is no specific clinical correlate to a positive anesthetic block response .
Young, et al, and Laslett, et al[3-8] demonstrated that there are clinical prediction rules that can be helpful in differentiating lumbar zygapophysial joint from sacroiliac joint or discogenic pain. Young, et al and Laslett, et al concluded that a negative extension-rotation test, presence of the centralization phenomenon, and pain when arising from flexion pointed strongly away from the likelihood of a positive LZJ block response. The presence of 3 or more of five clinical signs: age >49, symptoms best walking, symptoms best sitting, onset pain is paraspinal, and positive extension/rotation test, yields a sensitivity of .85, specificity of .91, PPV of .55, NPV of .98, and a positive likelihood ratio of 9.7 when measured against a standard of 95% relief of pain to a single block [set].
Sacroiliac joint mediated pain may be symptomatically similar to and difficult to distinguish from lumbar Z-joint mediated pain. However, if maximal pain is below the level of L5, then SIJ pain is more likely. van der Wurff found that when 3 or more of 5 positive provocation tests (distraction, compression, thigh thrust, Gaenslen’s, FABER) are positive, there is a sensitivity of .85, specificity of .79, PPV of .77, NPV of .87,and positive likelihood ratio of 4.02 of having true SIJ pain, as determined by comparative blocks.
Pain arising from the hip joint can cause significant pain and disability, and thus be a confounding factor with respect to subjects’ reporting of pain, function, or quality of life. To the extent possible, those with significant hip joint generated pain will be excluded from the study. The flexion abduction external rotation (FABER) and internal rotation overpressure (IROP) tests will be used as screening exclusionary tests as these were shown by Maslowski et al to have sensitivities of .82 and .91 and positive predictive values of .46 and .47 respectively, of a positive response to intra-articular hip block.
These findings and principles were incorporated into the inclusion/exclusion criteria so that, to the extent possible, only patients with a high likelihood of truly having Z-joint mediated pain would be screened (with dual medial branch blocks) for possible treatment with lumbar medial branch radiofrequency neurotomies. This approach may give some direction to clinicians on how to choose patients for potential lumbar Z-joint screening procedures. An additional intent of using these selection criteria is to optimize the cost efficiency of the use of diagnostic LZJ injections in clinical practice. However, realizing the limitations of clinical examination findings to determine Z-joint related pain, patients need to receive medial branch blocks to further determine the source of their pain, and for treatment decision making.
There is a hierarchy, in terms of maximizing diagnostic specificity, of diagnostic criteria with which to accurately diagnose lumbar zygapophysial joint pain[12, 13]. This hierarchy also applies to the selection of patients for lumbar medial branch (MB) radiofrequency neurotomy (RFN) procedures. The use of a single set of intra-articular or MB blocks will yield unacceptably high false positive diagnostic, and low RFN outcome, rates[14-18]. Conversely, the highest degree of specificity is achieved through the use of combined comparative (dual blocks with anesthetics of different duration with corresponding duration of pain relief) and placebo blocks[12, 19, 20]. This strategy is not without its own drawbacks such as added expense and risk exposure to patients, and the ethical questions associated with the use of placebo blocks. It is believed that the use of dual MBBs is the most desirable method with which to select candidates for RFN. This can be done with comparative blocks, modified comparative blocks, or dual blocks without regard to relative duration of pain relief. Considering the placebo controlled work of Lord et al , time- contingent relief with dual blocks (longer relief with bupivacaine than lidocaine) yields a false negative rate of 46%, and a false positive rate of 12%, whereas non time-contingent dual medial branch blocks yields a false negative rate of 0%, but a false positive rate of 35% . This latter method is believed by the clinicians at Denver Back Pain Specialists (www.denverbackpainspecialists.com) and others  to provide a reasonable and practical level of diagnostic certainty for clinical and research use, while not excluding patients who might benefit from treatment. The use of an 80% or better level of pain relief, as marked by the patient on a 6 hour pain relief diary post procedure, for the duration of the anesthetic used, is believed to be an acceptable level of relief for use with diagnostic blocks . The prevalence of true lumbar zygapophysial joint/ medial branch mediated pain in the population studied with dual medial branch blocks also has an impact on the diagnostic confidence of those blocks. Time-contingent dual blocks in a population where the prevalence is 40% allows for a diagnostic confidence of 85% and a confidence of 66% if non time-contingent blocks are used. If the prevalence is 15%, then time-contingent blocks provide a 60% level of confidence and non time-contingent blocks a level of 32%. The block paradigm noted to be the optimal blend of rigor and practicality for the selection of patients for LMB RFN, at Denver Back Pain Specialists, is that of non time-contingent dual medial branch blocks with 80% or greater relief of index pain (resulting NPR 0-1), with pain relief from bupivacaine blockade lasting at least 3 hours and that of lidocaine lasting at least 2 hours. This should be, when possible, combined with patient screening using clinical examination (see above) in an attempt to increase the prevalence of true LZJ pain in those selected for medial branch blocks.
Medial branch blocks, performed at Denver Back Pain Specialists, are always conducted using the International Spine Intervention Society (ISIS) technique .
Exceptions to the “Rules” and Cost Considerations
The diagnostic paradigm noted above is clearly the preferred method of selecting patients for lumbar medial branch (and L5 dorsal ramus) radiofrequency neurotomy. Practical and cost concerns must always be considered in clinical practice, however, and alternate clinical methods are acceptable for individual patients. For instance, intra-articular zygapophysial (facet) joint blocks are occasionally used in place of the first set of medial branch blocks [for RFN candidate selection] but should not be used as a stand-alone selection procedure. There has been discussion in the literature  questioning the cost effectiveness of using two sets of medial branch blocks, as opposed to zero or one set, for RF patient selection. Dr. Bainbridge has presented the two-block argument at an international pain conference, in a point/counterpoint fashion. The PowerPoint presentation can be found below (www.denverbackpainspecialists.com > Subject Reviews).
Dr. Derby, et al have conducted and presented (ISIS Annual Scientific Meeting 2011) compelling evidence for both the ability to predict positive RF outcomes, and in support of the cost-effectiveness of using a single set of medial branch blocks for patient selection. This requires a very definitive (greater than 70 or 80 % relief of pain) response to this single set of blocks, however.
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