THERE ARE A WIDE VARIETY OF POTENTIAL PAIN generators in the spine, including the zygapophysial joints, intervertebral discs, nerve roots, sacroiliac joint, muscles, tendons, and ligaments. Interventional pain management techniques are performed for either diagnostic or therapeutic purposes. Ideally, prior to the procedure a thorough history and physical examination have been performed and a specific diagnosis has been made. The procedures should be target specific and performed in a technically sound manner with proper technique. Current literature suggests that in some cases procedures performed without guidance (i.e., “blind”) that are not target specific may not be better than sham treatments; although there may be indications for such procedures in certain conditions, they will be sparingly covered in this chapter. Other injections that are target specific but do not have credible efficacy data will also not be discussed.
Additionally several key principles must be considered when reviewing the literature for interventional procedures, including the importance of categorical outcomes, appropriate time frame for follow-up, and the effects of heterogeneity and prevalence data on outcomes. These will all be discussed prior to reviewing the general indications for and evidence of efficacy for the various techniques that target a variety of pain generators. Therefore, each section will cover the basic principles and evidence-based outcomes for the respective interventions, including procedures targeting the zygapophysial joints, intervertebral discs, the epidural space, and the sacroiliac joint.
GENERAL PRINCIPLES FOR REVIEWING EFFICACY DATA IN PAIN LITERATURE
Prior to reviewing the types and efficacy of pain interventions, it is important to understand the method of analysis. Studies have found that as little as 30% of pain relief may be clinically meaningful in chronic pain conditions.1 Fifty percent of pain relief has been established as what patients consider “much improved” for pain in general and improved quality of life, and is also the minimal clinically important change for radicular pain.1–3 Subsequently, in the pain literature 50% of pain relief is the most commonly used dichotomous outcome measure.4 Studies failing to reach these thresholds do not demonstrate a clinically meaningful outcome, despite at times being statistically significant.
An appreciation of the distribution of the outcome variables is critical in correctly interpreting the data. Unfortunately, a common method to report outcomes from pain studies which utilize the visual analog scale (VAS) pain scores is by comparing the mean pain scores of the groups without regards to the distribution of the data. However, for this to be a statistically valid way to analyze ordinal VAS data, the assumption is that VAS pain scores are normally distributed. Unfortunately, pain scores are rarely, if ever, normally distributed.
Consider that if an intervention is successful in achieving significant relief in a portion of subjects, there will be two distinct groups when analyzing outcome data. One group of responders will be distributed around a low VAS value, and ...