The Difficulty of Diagnosing Sacroiliac Joint Pain
Pain coming from the sacroiliac (SI) joint can be difficult to diagnose. That's because the problem can be inside the joint (intraarticular) or it can be extraarticular (outside of the joint). Extraarticular structures include ligaments and muscles. And the diagnosis is made more difficult by the fact that pain coming from the SI joint can be felt in the buttock, groin, and/or leg -- not just in the area of the sacroiliac joint.

There isn't one single test that can be used as the gold standard in diagnosis. Instead, doctors use a variety of pain provocation tests and/or joint injection with a numbing agent combined with an antiinflammatory medication. Pain provocation tests stretch, compress, or contract tissue structures around the SI joint. Injection numbs or silences the pain-generating structures.

But there are questions about how valid, reliable, and sensitive or specific these tests are. In order to help those who examine the sacroiliac joint, the authors of this report conducted a systematic review of diagnostic tests for sacroiliac pain. The researchers (from The Netherlands) looked at all published studies on tests to diagnose SI joint pain.

They used the diagnostic criteria set out by the International Association for the Study of Pain (IASP). The IASP proposes that 1) SI joint pain can be identified by the location of the painful symptoms, 2) SI joint pain will be reproduced by carrying out the provocation tests, 3) And the pain will go away after injection with the numbing agent. But is this really so? There are some experts who say both sets of tests are needed. And even then, the results are not 100 per cent full-proof.

In the studies included in this review, both sets of tests were performed with a day apart but no more than seven days separating them. The goal was to avoid influencing the results of one test by the use of the other test. The hope is to find a test that is 100 per cent sensitive and specific. That means the results of the test would always be positive in patients with an SI problem and negative when the pain wasn't coming from the SI joint.

A reference standard was used in all studies included in the analysis that were using intraarticular injections as a diagnostic test. In this case, it means that before patients received an intraarticular injection with a local anesthetic, the placement of the injected material was checked first. This was done by injecting a small amount of dye into the joint. In this way, it was possible to make sure the injection really got where it was intended (inside the SI joint).

A second important feature of the studies included was how they defined success of the injection. All studies agreed that at least 50 per cent pain reduction was required. And it had to last at least one hour. Most studies defined success as 75 to 80 (up to 90) per cent pain reduction.
Studies comparing the use of an intra-articular injection confirmed that patients definitely got pain relief. No one getting a placebo (pretend) injection got 70 per cent or more of pain relief.

Attempts to analyze provocation tests were met with less success. Of the five tests included (compression, distraction, thigh thrust, Gaenslen's test, and Patrick's test), only results for the thigh thrust test and the compression test could be included.

Studies of the other tests were just too different in how they were carried out to include them. That doesn't mean these tests didn't have good diagnostic validity. It just means there's a need for better, more consistent (across different studies) designs for future studies.

The authors conclude from their analysis of the many studies in this systematic review that just using the location of pain as a diagnostic tool is not a valid approach. Too many patients with pain around the SI area end up with a problem originating someplace else. And too many patients with true SI joint problems have buttock, leg, or back pain (not SI joint pain).

With that out as a gold standard, two of the pain provocation tests might be helpful but they don't really isolate exactly where the problem is coming from. For example, is it ligamentous? If so, which one(s) is involved? The same goes for muscles -- is there a muscular problem and if so, which one is generating the pain signals and why? The source of pain could be the joint capsule (outside the joint) or the joint articular (cartilage) surface (inside the joint)? None of the compressive tests really sort this out carefully enough.

That leaves us with the intraarticular injection as a potential gold standard diagnostic test. But the authors point out that the numbing agent can leak out of the joint affecting the nearby nerves and soft tissues. Thus, the injection cannot be designated as the single most reliable and valid test for SI problems either.

Until and unless scientists can figure out how to isolate individual structures in and around the SI generating pain, it remains certain that one individual diagnostic test just isn't going to be possible. For now, it has been suggested that examiners use the provocation tests best known for their ability to recreate pain from the SI. The presence of a positive thrust test and positive compression test signal the need for further diagnostic workup with an intraarticular injection.

That brings us back to the International Association for the Study of Pain (IASP) and their criteria for the diagnosis of SI joint pain. These make a nice place to start, but there isn't enough evidence to support them as reliable and valid diagnostic guidelines at this time.
Karolina M. Szadek, et al. Diagnostic Validity of Criteria for Sacroiliac Joint Pain: A Systematic Review. In The Journal of Pain. April 2009. Vol. 10. No. 4. Pp. 354-368.