The promise of an effective treatment for sacroiliac-related low back pain.

BACK pain is the most frequent type of pain reported by adults, with more than one fourth of adults in the United States having had at least one episode of back pain within the past 3 months. In 2002, office visits for back pain in the United States totaled 890 million, comprising 2.3% of all office visits. The economic impact of low back pain is large and seems to be growing. Sacroiliac joint dysfunction is estimated to be the underlying cause in 15–25% of patients who have persistent low back pain. Diagnosing pain related to sacroiliac dysfunction is difficult, because findings on history and physical examination and diagnostic radiography are unreliable; placement of intraarticular local anesthetic has become the gold standard, but this too is plagued by a frequent placebo response that decreases the diagnostic specificity. Even more problematic has been the search for an effective treatment for sacroiliac-related pain. Treatments currently in use range from targeted exercise programs to surgical fusion, and none of these have proven effective. Pain related to sacroiliac joint dysfunction is common, and a safe and effective treatment would address a major unmet medical need. In this issue of ANESTHESIOLOGY, Cohen et al. have tested a new type of radiofrequency neurolysis for treatment of sacroiliac joint pain. The use of radiofrequency neurolysis of the medial branch nerves has shown modest success in reducing low back pain associated with lumbar facet arthropathy. Based on the technique used for treating the lumbar facets, a number of investigators have developed strategies for applying radiofrequency neurolysis to the sacroiliac joints. However, the effectiveness of this approach has been limited, typically producing significant pain reduction (50% or more) lasting for several months in less than half of carefully selected patients. Investigators believe that these limited treatment effects may stem, in part, from limitations inherent to the radiofrequency technology and our limited knowledge of the anatomy of the innervation of the sacroiliac joint. The morphology of radiofrequency lesions is well known. The extent of the lesion anterior to the active tip of the treatment cannula is limited, therefore, the cannulae must be placed in such a way that the nerve that is targeted lies along the side or shaft of the cannula, where the size of the resulting lesion is largest. This does not present a problem when treating the lumbar facets, because the needle can be advanced over the transverse process to bring the entire length of the active tip of the radiofrequency cannula in to close apposition to the medial branch nerve. However, placement of lesions over the posterior sacrum is more problematic, because the tip of the cannula is perpendicular to the plane of the sacrum where the sacral lateral branch nerves supplying sensory innervation to the sacroiliac joint are accessible for treatment, limiting the volume of the lesion placed adjacent to each nerve, and likely leading to treatment failure simply because the lesion did not encompass the targeted nerves. When difficulties related to the treatment cannulae are coupled with a heretofore poor understanding of the anatomy of the sensory innervation to the sacroiliac joints, it is not surprising that previous studies have demonstrated limited success. Cohen et al. have tested the effectiveness of a new adaptation of radiofrequency technology called cooledprobe technology in treating sacroiliac joint pain. Cooled radiofrequency was designed to overcome some of the limitations of conventional radiofrequency technology. This new technology uses a treatment cannula that is cooled by a continuous flow of water within the shaft of the cannula itself, thus limiting the rate of heating at the tip of the cannula. This leads to delivery of significantly greater energy to the tissue surrounding the cannula and results in a lesion that extends anterior to the active tip. Therefore, using cooled radiofrequency, the cannula can be placed perpendicular to the course of the nerve to be treated and, in this position, can be expected to incorporate the nerve within the resulting lesion. Recent study of the innervation of the sacroiliac joints demonstrates that the sensory nerves supplying the posterior sacroiliac joint lie in a predictable location relative to the sacral foramina. Combining this new technology with a better understanding of the anatomy has led directly to the new treatment detailed in the study of Cohen et al. The results of Cohen et al. demonstrate greater than 50% pain relief and significant functional improvement in the majority of patients receiving active radiofrequency treatment, and these improvements are sustained in the majority of patients for 6 months after treatment, in comparison to only 14% of patients receiving sham treatment, who had significant improvement at 1-month follow-up and none beyond that time. It is exciting to think that we might well have a new and effective treatment for sacroiliac-related pain, but caution is in order. This is a very small randomized conThis Editorial View accompanies the following article: Cohen SP, Hurley RW, Buckenmaier CC III, Kurihara C, Morlando B, Dragovich A: Randomized placebo-controlled study evaluating lateral branch radiofrequency denervation for sacroiliac joint pain. ANESTHESIOLOGY 2008; 109:279–88.