Sacroiliac joint pain: provocation test clusters, not palpation

The pelvis that "feels uneven"

Buttock pain below the belt line is a familiar presentation in manual therapy clinics, and so is the examination that often follows. Thumbs on the posterior superior iliac spines, a look at the anterior spines, a standing flexion test, maybe a long-sitting test. One side seems higher or moves differently, and the explanation writes itself: the pelvis is rotated, the joint is stuck, we'll put it back.

Most of us were taught some version of that sequence. The trouble is that the research on sacroiliac joint (SIJ) examination split, years ago, into two quite different questions, and only one of them has a useful answer. If you are still examining the SIJ mainly by palpation and motion testing, you are using the half of the evidence that never held up.

This article is about the other half: what pain provocation tests can and can't tell you, how to combine them, what to rule out first, and what a positive finding should change in clinic.

SIJ pain and SIJ dysfunction are not the same thing

Laslett's evidence review in the Journal of Manual & Manipulative Therapy (2008) draws the distinction clearly. SIJ pain is pain arising from the structures of the joint. SIJ dysfunction usually refers to an aberrant position or movement of the joint, which may or may not be painful.

That difference matters because the two have very different evidence bases. Tests for dysfunction generally have poor inter-examiner reliability, and there is no readily available reference standard for "dysfunction", so their validity is unknown. Tests that stress the joint to reproduce the person's familiar pain have acceptable reliability and clinically useful validity against an accepted reference standard.

In other words, you can test whether the SIJ is a likely source of someone's pain. You can't reliably test whether it is out of position.

What palpation and motion tests have shown

The reliability problem with motion and position testing is long-standing. Van der Wurff and colleagues' systematic methodological review of reliability studies (Manual Therapy 2000) could not demonstrate reliable outcomes for SIJ mobility tests and concluded there was no evidence on which to base accepting them into daily practice. Pain provocation tests looked more promising, with the Gaenslen and thigh thrust tests showing reliable results in two studies.

Robinson and colleagues (Manual Therapy 2007) then had experienced manual therapists examine 61 people on the same day. Agreement for the pain provocation tests ranged from 67% to 97%, with kappa values from 0.43 to 0.84. Clusters of provocation tests also had good agreement (kappa 0.51 to 0.75). For the palpation test, agreement was 48% and kappa was −0.06. That is no better than chance.

There is also a validity problem with positional findings. Tullberg and colleagues (Spine 1998) used roentgen stereophotogrammetric analysis in ten people whose SIJ tests indicated unilateral dysfunction. After manipulation, the positional tests normalised. The measured position of the sacrum relative to the ilium did not change in any of them. The authors concluded the positional test results were not valid, while being careful to say their study neither proved nor disproved clinical benefit from manipulation.

So the change you find when you retest after a technique is real, in the sense that the test result changes. It just isn't the joint moving back into place, and the test that "confirmed" it was never measuring position.

The reference standard, and why it needs care

To judge any clinical test, you need something to compare it with. For SIJ pain, that reference is an image-guided anaesthetic block into the joint: if the person's familiar pain is substantially relieved, the joint is considered the likely source.

Blocks have their own limits. Laslett's review notes that false-positive responses to single diagnostic blocks of synovial joints are common, so comparative or placebo-controlled blocks are now considered necessary before SIJ-mediated pain is confirmed. Pain from ligaments outside the joint cavity may not be captured by an intra-articular block at all.

Using blocks, Schwarzer and colleagues (Spine 1995) studied 43 consecutive people with chronic low back pain felt maximally below L5–S1. Thirteen (30%) obtained substantial relief from an SIJ block, and groin pain was the only referral pattern associated with a positive response. That is one study, using a single anaesthetic block. It is enough to say the SIJ is a genuine pain source for some people, and not enough to say what proportion of your caseload it explains.

Szadek and colleagues' systematic review (Journal of Pain 2009) makes the same point from the other direction. Across 18 studies the block technique, medication and required degree of relief varied considerably, and the authors advise that the diagnostic validity of SIJ tests should be regarded with care because a true gold standard is lacking.

What the provocation clusters show

The key provocation tests described in the literature are distraction, compression, thigh thrust, Gaenslen's test and sacral thrust. Each applies a stress through the SIJ and asks one question: does that reproduce the pain you came in with?

Single tests are often positive in people whose pain does not come from the joint. Laslett's review points out that provocation tests are positive in back pain patients more often than SIJ pain is thought to occur, which is why a diagnosis has to rest on several positive tests rather than one.

The combined findings are reasonably consistent:

• Laslett and colleagues (Manual Therapy 2005) examined 48 people who then received an SIJ injection. Three or more positive tests out of six had a sensitivity of 94% and specificity of 78%. Any two of four selected tests also had strong predictive power, with the greatest area under the curve of any composite (0.842). Everyone who responded to the injection had at least one positive test, and when none of the six tests reproduced familiar pain, the SIJ could be ruled out as a current source of low back pain.
• Van der Wurff and colleagues (Archives of Physical Medicine and Rehabilitation 2006) compared a five-test regimen with fluoroscopically controlled double blocks in 60 people with chronic low back pain. Three or more positive tests gave a sensitivity of 85% and specificity of 79%, a positive likelihood ratio of 4.02 and a negative likelihood ratio of 0.19.
• Szadek and colleagues (Journal of Pain 2009) pooled data against double blocks. The thigh thrust test (diagnostic odds ratio 18.5), the compression test (3.9) and three or more positive stressing tests (17.2) all showed discriminative power, with wide confidence intervals.

The practical reading is that a cluster of three or more positive tests meaningfully raises the probability that the SIJ is involved, and an entirely negative cluster makes it unlikely. Neither result is a diagnosis in isolation.

Check for centralisation first

The most useful refinement came from adding a lumbar question before the SIJ question.

In Laslett's 2003 study (Australian Journal of Physiotherapy), 48 people with chronic lumbopelvic pain referred for spinal injections were examined using repeated movement testing as well as SIJ provocation tests, then received diagnostic SIJ injections. Eleven had SIJ pain confirmed by double injection. In the main subset analysis of 34 people, which excluded those whose symptoms centralised with repeated movements, the clinical examination had a sensitivity of 91%, a specificity of 83% and a positive likelihood ratio of 6.97. It was more accurate than the provocation tests alone.

Laslett's later review used these data to estimate a post-test probability of about 77% when three or more provocation tests are positive and symptoms cannot be made to centralise, from a pre-test prevalence of 32% in that referred sample.

The clinical sequence follows directly. If repeated lumbar movements make the pain move towards the spine, think lumbar before you think SIJ. If they don't, the provocation cluster becomes much more informative.

What a positive cluster doesn't tell you

A positive cluster says that stressing the SIJ region reproduces the person's familiar pain. It doesn't tell you the joint is displaced, which direction to correct, or why the joint is painful.

It also doesn't tell you which treatment works. Laslett's 2008 review was explicit that, at that time, no studies had examined treatment efficacy in a cohort with SIJ pain confirmed by comparative or placebo-controlled blocks. The review suggested specific lumbopelvic stabilisation training and intra-articular corticosteroid injection as the treatments most likely to help, but that was a judgement about where research should go next, not proof of effect.

What a better diagnosis does change is the explanation. "Your pain is coming from around the joint at the back of your pelvis, and it's sensitive to load at the moment" is supported by the examination. "Your pelvis is out" isn't, and it hands the person a reason to worry every time it "goes" again.

When the SIJ question is really a rheumatology question

Provocation tests tell you a sensitive structure is being stressed. They can't tell you that the cause is mechanical. Axial spondyloarthritis often presents as buttock and low back pain in younger adults, and it is easy to miss when every examination finding seems to point at the joint.

NICE's spondyloarthritis guideline (NG65) gives a referral rule that fits any MSK assessment. If low back pain started before age 45 and has lasted longer than three months, refer to a rheumatologist for a spondyloarthritis assessment when four or more of these are also present:

• low back pain that started before age 35
• waking in the second half of the night because of symptoms
• buttock pain
• improvement with movement
• improvement within 48 hours of taking NSAIDs
• a first-degree relative with spondyloarthritis
• current or past arthritis
• current or past enthesitis
• current or past psoriasis

If exactly three are present, NICE advises an HLA-B27 test and referral if it is positive, which for many MSK clinicians means involving the GP. The same guideline warns not to rule spondyloarthritis out on any single sign, symptom or test result, and notes that it affects a similar number of women as men, can occur in people who are HLA-B27 negative, and may be present with a normal plain X-ray of the sacroiliac joints.

Pelvic girdle pain, including pain related to pregnancy, has its own guidance. The European guidelines on pelvic girdle pain (Vleeming and colleagues, European Spine Journal 2008) recommend diagnosis using pain provocation tests (the posterior pelvic pain provocation or thigh thrust test, Patrick's FABER, Gaenslen's test and the modified Trendelenburg test), palpation of the long dorsal ligament and the symphysis for pain, and the active straight leg raise as a functional test. They specifically do not recommend mobility palpation tests, X-ray, CT, scintigraphy or diagnostic injections for this purpose.

What changes on Monday morning

For the next person with buttock or posterior pelvic pain:

1. Stop diagnosing from landmark asymmetry or motion tests. If you still palpate, don't tell the person their pelvis is rotated or out of place on the strength of it.
2. Ask the lumbar question first. Use repeated movement testing to see whether symptoms centralise before you interpret SIJ tests.
3. Run the provocation cluster and count. Record which tests reproduce familiar pain, not just any discomfort. Three or more positive with no centralisation makes the SIJ a likely source. A completely negative cluster makes it unlikely.
4. Screen for inflammatory back pain. Under 45 with more than three months of symptoms, work through the NICE NG65 criteria and act on them.
5. Explain in terms of sensitivity and load. Describe the joint region as a likely pain source that is currently sensitive, not a bone that needs putting back.
6. Write it down. Note the tests, which were positive, the centralisation result and the inflammatory screen. That record is what lets you, or a colleague, change course if the plan isn't working.

None of this needs new equipment. It needs us to stop trusting the part of the SIJ examination that never had the evidence behind it, and to use the part that does.