Anesth Analg 2007; 105:1523-1525
© 2007 International Anesthesia Research Society
doi: 10.1213/01.ane.0000287649.46276.e6
EDITORIAL
Studies on Diagnostic Injections and Surgery for Low Back Pain: Problems, Advances, and Opportunities
Honorio T. Benzon, MD
From the Department of Anesthesiology, Northwestern University Feinberg School of Medicine, Chicago, Illinois.
Address correspondence to Honorio T. Benzon, MD, Department of Anesthesiology, Northwestern University Feinberg School of Medicine, Chicago, IL. No reprints available. Address e-mail to hbenzon{at}nmff.org.
The Medical Intelligence Article by Cohen and Hurley (1) is a scholarly distillation of articles on the prognostic ability of diagnostic spinal injections in predicting outcomes after back surgery. Pain medicine interventionalists are frequently being called upon by back surgeons to perform diagnostic injections to help them decide whether surgery should be performed and at which vertebral levels. Based on the evidence, Cohen and Hurley arrived at reasonable conclusions on the limited role of these blocks in predicting surgical outcomes. This editorial is a discussion of the problems with diagnostic spinal injections, the advances in surgery of the back, and opportunities for more uniform studies on back pain.
There are several problems in the performance of and interpretation of the results of diagnostic spinal injections. Diagnostic spinal nerve root blocks lack specificity, as shown by a study wherein selective nerve root block, medial branch block, and even sciatic nerve block relieved the pain of lumbosacral radiculopathy (2). The exact volumes of local anesthetic required to improve the specificity of nerve root blocks is not known. Injection of a 1–2 mL volume in nerve root blocks may result in unintentional epidural blockade through the intervertebral foramina or blockade of other nerve roots (3). For medial branch blocks, a 1–2 mL volume may be too much, but is 0.5 mL adequate? For facet joint injections, injection of volumes larger than 1–2 mL may rupture the joint with overflow of the injectate into the epidural space and surrounding nerve root. For discography, there is presently no agreement on the volume of radiographic contrast or the role of manometry. The performance of several nerve root blocks with different anesthetics has been recommended by some investigators (4) and correlations made between the duration of pain relief and the known duration of the local anesthetic. Such correlations, however, may be unreliable, because it is not uncommon for the duration of pain relief to outlast the duration of the local anesthetic when the cycle of pain is broken. Regarding anatomy, we are often not really sure of the exact location or course of the nerve we are blocking. For example, variations in the anatomy of the lateral branches of the posterior primary ramus of the S1 to S3 dorsal rami were not elucidated until recently (5). For nerve root blocks, overlapping of dermatomes and sensory innervations makes it difficult to determine the involved nerve root. Thus, most diagnostic nerve blocks, unfortunately, lack precision and specificity.
The other issues with diagnostic blocks are its unidimensionality and the difficulty in interpreting partial responses. The end-point of diagnostic blocks is pain relief. Yet pain is multidimensional, as defined by the International Association for the Study of Pain and diagnostic blocks do not consider the emotional and functional components of pain. If the pain is partially relieved, is it because it is partly sensory and partly psychological or central in nature? Or is it because the block was partial or incomplete? The completeness of sympathetic blocks can be evaluated with some certainty (6,7) but the completeness of some of the diagnostic spinal injections (e.g., blockade of the medial and lateral branches of the posterior primary rami) cannot be determined. The success of spinal injections, diagnostic or therapeutic, is based on "more than 50% relief" (1). This criterion is not shared by studies on acute pain and pharmacologic management of chronic pain. Because the criterion of success is not stringent, the predictability of diagnostic spinal injections is modest as a consequence.
Ultimately, diagnostic blocks are intended to select patients for back surgery, but how effective is surgery? Previous studies on surgery for low back pain have been wanting in quality; most studies were either retrospective or case series with minimal follow-up. Before 1990, only one study was randomized (8), and only a few studies were notable for the long-term follow-up of the patients (9,10). It has only recently that studies on surgery for herniated disk and spinal stenosis have been prospective, randomized, and with a control group (11–15) (Table 1). Interestingly, none of the studies used diagnostic spinal injections to determine the site(s) of the surgery, but these recent publications provide for a more rational decision on the part of physicians and patients (16,17).
In the future, better outcome measures for studies on back pain are needed to evaluate any type of therapy. Previous studies on low back pain had very few outcome measures and measurement tools. The original recommendations for outcome measurements in studies on low back pain (18) now appear to be inadequate, other outcome measures have been used to provide a more complete assessment of the patient’s pain and physical and functional impairments (12–15,19–21) (Table 2). The use of these outcome measures in future studies on back pain provide opportunities for better and more uniform studies, the results of which are more acceptable and amenable to meta-analyses.
The article by Cohen and Hurley provides us a current understanding of the role of the diagnostic spinal injections. Prospective, randomized, controlled studies on surgery have been published recently and more stringent studies are probably being undertaken. The future of patients with back pain has become more promising, appropriate decisions are now being made based on studies of highest quality.
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Footnotes
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Accepted for publication August 13, 2007.
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