The Question of whether or not SIJ or pelvic girdle pain (PGP) may originate from the long dorsal ligament.

In a blog publication https://thescandiphysio.com/ 26 April 2026, Simen Sletten states that posterior longitudinal ligament pain is at least as common intra-articular sacroiliac joint pain, and I wondered what that was based on. Here is the statement:

“A potential source for extra-articular nociception is the “long dorsal ligament”, also called long posterior sacroiliac ligament. This ligament is anatomically connected to the erector spinae muscle and other structures, and it also shares innervation with the SIJ. According to an article, the long dorsal ligament pain is at least as common as SIJ pain itself (2).”

The citation is:

McCormick ZL, Hurley RW, Anitescu M, Bhaskar A, Bhatia A, Cassidy RC, et al. Consensus practice guidelines on sacroiliac joint complex pain from a multispecialty, international working group. Pain Med. 2025 Dec 1;26(12):817–917. doi:10.1093/pm/pnaf129 PubMed PMID: 41318933; PubMed Central PMCID: PMC12681192.

So, I asked Grok this question:

"Are there any studies comparing clinical tests for long dorsal ligament pain with a valid or plausible reference standard? If so, what is the sensitivity and specificity of the tests? Also, are there any reliability studies of clinical tests for long dorsal ligament pain?"

The response summary is:

"The main relevant studies use a plausible clinical reference standard for PGP (history of peripartum pelvic pain + positive posterior pelvic pain provocation [P4] test and/or active straight leg raise [ASLR] test). This is not a definitive “gold standard” (e.g., no fluoroscopy-guided diagnostic injection or imaging specifically targeting the dorsal ligament, which is a known limitation for extra-articular SIJ/ligament pain). No studies were identified using injections or other objective gold standards specifically to validate the LDL palpation test against confirmed LDL pain."

I think the claim that palpation for tenderness (though having some level of inter-tester reliability) is a valid test for a condition is problematic. Especially as the validity studies compare it to another cluster of clinical tests in PGP patients - a highly selected group, even if the group has the highest incidence of SIJ pain.

You can make a good case that the tests and the reference standard to which it has been compared, are both worthy of further study. Such a study should compare both of these clinical tests to an independent and blinded criterion standard, such as local anesthetic block into the long dorsal ligament. Once you have diagnostic accuracy values for that comparison, it will be easier and more valid to estimate the prevalence of long dorsal ligament pain.

My main concern and scepticism comes from the fact that tenderness at or below the PSIS is (in my experience) extremely common among patients with known sources of nociception from the disc and lower facet joint. I think the sensitivity of that palpation would be high, but the specificity low. Just my opinion.