Over the years, there’s been a lot of debate about the source of pain felt in the sacroiliac joint (SIJ). Is it coming from the joint itself? From outside the joint? Or both? Injecting a numbing and antiinflammatory (steroid) agent into the SI joint has convinced scientists that pain can come from the joint. Relief of pain after injection is proof of that.
But what about the many patients whose pain isn’t relieved by an injection into the SIJ? Would injecting this same pain reliever and steroid outside (but near) the joint help? In this study, the surgeons split the total usual dose of medication in half. They injected half into the SIJ and the other half under the posterior sacroiliac ligaments at the S1-3 level.
Patients included in the study had low back pain along with pain in the buttock, thigh, groin, or lower leg. The back pain was below the L4 level in the region of the sacroiliac joint. All patients had been treated by a physical therapist but did not respond to therapy. Those that had a previous injection for other problems such as spinal stenosis, facet syndrome, or disc herniation were allowed in the study if that injection failed to improve their symptoms.
Since this group of researchers had already published a study on the benefit of intraarticular injections, they could compare the results of this new split injection with results from the standard single injection. By doing so, they hoped to be able to show that sacroiliac joint pain isn’t just caused by problems inside the joint. And they believed that the current practice of using intra-articular injections to diagnose sacroiliac joint dysfunction underestimates the true number of patients affected by this problem.
Their thinking was that it’s possible for soft tissue structures surrounding the joint to generate the same pain pattern as the joint itself. They also took the opportunity to see what kind of long-term results the patients got with injection therapy. Finding a treatment with long-lasting results would be very helpful in managing this painful condition.
Pain (rated from zero to 10) was used as the main measure of success. Everyone kept a pain diary with pain ratings from before the injection, three weeks after the procedure, and again three months postinjection. Follow-up was kept fairly short to avoid the problem of evaluating new pain patterns that might develop. The evaluation and treatment of new problems could interfere with the comparison of SI joint intra-articular and extra-articular injections.
The authors used a second tool (the AIAT) to measure functional outcomes. This self-report survey was developed for use by the pain clinic where this research was done. The AIAT measures overall improvement in daily activities such as housework, shopping, childcare, work, and mobility. Points are awarded and a score of zero (worse), one (no change), two (slightly better), three (greatly improved), or four (restored to normal) determines the results. It is a tool that has been tested and validated for measuring patients’ (with back pain) responses to treatment.
Change in scores from before to after treatment offer a way to measure response rate as a change in percentage. Success was defined on the pain scale as a 50 per cent change (improvement) from before to after treatment. A score of three or higher on the AIAT test was considered an indication of success. Scores from the two tests (pain and function) were cross checked to see if one could predict the other. Any differences between the two groups were reviewed carefully.
The results showed that the combined procedure had better results than the intra-articular injection alone. Improvements were more noticeable at three months after treatment (compared with three weeks after injection). From a statistical analysis point of view, the combined block procedure had a sensitivity level of 88 per cent, a specificity of 49 per cent, and a positive-predictive value of only 44 per cent.
Sensitivity shows how well the diagnostic test determines a true positive for SIJ pain (the patient really does have an SIJ problem). Specificity reflects the ability of the same test to show a true negative (the person really doesn’t have an SIJ problem). Positive predictive value is the proportion of the total number of patients in the study with a positive test who were correctly diagnosed. This value is more clinically meaningful than sensitivity but all three measures (sensitivity, specificity, and positive predictive value) are all important ways to evaluate a new test procedure.
Patients who had their symptoms more than three years, who smoked, or whose symptoms were made worse by walking, climbing stairs, and standing were more likely to have a negative outcome from the combined procedure. For the single injection treatment, age and duration of symptoms had a weak effect on the response to treatment at the three-month check-up. Older patients and patients whose symptoms had been present the longest seemed to have the poorest response rate. Correlation between the two tests was quite strong. This means if one test was positive, it’s likely the other test will also be positive.
All in all, it looks like injecting a numbing agent and steroid into the SI joint and also around the posterior interosseous ligament is a successful treatment for patients with chronic SI pain. The results support and confirm the findings of several other studies that reported sacroiliac joint pain can come from outside the joint. The number of patients who experienced pain relief with the dual blocks increased by 47 per cent over just the single injection.
Despite these reported findings, the authors point out that the evidence wasn’t enough to make the claim that a combined sacroiliac and S1-3 injection is clearly better than a single sacroiliac injection alone. The next step in this research process is to compare four groups of patients: 1) single intra-articular injection, 2) single extra-articular injection, 3) combined intra- and extra-articular injection, and 4) placebo injection. Only when these additional studies are done, will we know for sure how common a true SI joint problem is and which block technique works best.