This is a short anatomical study about the superior cluneal nerves or dorsal rami.
They decided to perform an anatomical study to see what the ILIAC TRIGGER POINT that is located 7 to 8 cm from midline over the iliac crest could correspond to.
Some other authors say that the ILIAC TRIGGER POINT corresponds to the iliolumbar ligament attachments, but the authors of this article disagree and want to perform cadaveric dissections to prove their point. They think that the iliac trigger point corresponds to the point where the dorsal rami or cluneal nerves cross the thoracolumbar fascia. There they may get entrapped while crossing an osteofibrous tunnel on the rim of the iliac crest.
They dissected 37 cadavers and explained all the anatomic variations that the cluneal nerves can present.
About the authors: Robert Maigne (1923-2012) and Jean-Yves Maigne (rheumatologist).
Trigger Point of the Posterior Iliac Crest: Painful Iliolumbar Ligament Insertion or Cutaneous Dorsal Ramus Pain? (An Anatomic Study)
By Jean-Yves Maigne and Robert Maigne
The authors said that LOW BACK PAIN is a syndrome with various etiologies. In some cases, physical examination of soft tissues reveals TRIGGER POINTS.
Their definition of trigger points is: Points of maximum tenderness, where pressure reproduces actual pain.
The authors admit to being intrigued about the rather precise position and the frequent occurrence of what they call “the ILIAC TRIGGER POINT”.
The iliac crest trigger point
-The iliac trigger point is situated over the iliac crest at 7 or 8 cm from midline.
-As in the case of fibromyalgia, it can be associated to other trigger points.
-It can be unique and UNILATERAL in patients suffering from non-radiating, ipsilateral low back pain (patients present normal neurological examination, absence of tension signs, normal lumbosacral and pelvic roentgenograms or X-Ray).
Related proposed syndromes to the ILIAC TRIGGER POINT: The iliolumbar syndrome and the Thoracolumbar junction facet syndrome.
The iliolumbar syndrome was proposed by Hackett (1958) and Hirschberg (1979). It is characterized by posterior unilateral iliac crest pain. Tenderness upon what was thought to be the insertion of the iliolumbar ligament. It can also present referral pain into the groin or the lateral aspect of the hip and pain by contralateral bending. Anesthetic infiltration of this point ABOLISHES all signs and symptoms, and then the diagnosis is done.
The facet syndrome (by Robert Maigne) is characterized by a focal painful area in the dermatome of the cutaneous dorsal rami T12, L1. Anesthetic infiltration around the involved joint relieves the low back pain.
Thus, it can be seen that tenderness on palpation of the posterior iliac crest may correspond either to the insertion of the iliolumbar ligament or to the cutaneous dorsal rami (cluneal nerves). That way, the authors undertook this study to clarify the real cause. Especially by identifying the structures that ARE ACCESSIBLE to palpation during routine clinical examination.
Material and methods (dissections)
To perform this study they dissect 24 male cadavers and 13 female cadavers. Initially, they cut along the thoracolumbar fascia with a medial insertion, exposing the nerves. Then they dissected the nerves proximally to the intervertebral foramen to identify the level of origin and distally as their finest ramification would allow (even they used binocular lens).
Results of the anatomic study
The authors point out their theory: The iliolumbar ligament IS NOT ACCESSIBLE by palpation.
The iliolumbar ligament originates from the transverse process of L5 and inserts deep into the ventral margin of the iliac crest, 7 to 8 cm from midline. The insertion was shielded by the crest dorsally.
The dissection shows that the crest is usually crossed by two or three dorsal rami (cluneal nerves) that innervated the cutaneous layers of the buttock.
Anatomic variations:
- L1 was the most medial NERVE (22/37 dissections) and L2 was the most medial in the remaining 15 cases.
- L2 sometimes receives anastomosis from L3.
- The most lateral nerve was usually T12 (28 /37 dissections) or the L1.
The distance between the medial and the lateral branches varied from 1 to 5 cm.
The MEDIAL NERVE became superficial by passing over the CREST THROUGH AN OSTEOFIBROUS orifice consisting of thoracolumbar fascia and the superior rim of the ILIAC CREST.
The osteofibrous orifice was a rigid structure that in 2 instances was seen to SEVERELY COMPRESS THE NERVE.
Discussion about the iliac trigger point
-In the 37 dissections, the insertion of the ILIOLUMBAR LIGAMENT was always located on the VENTRAL ASPECT OF THE CREST. That led the authors to think that the iliolumbar ligament was INACCESSIBLE to palpation, since it is shielded by the crest.
Consequently, the trigger point located 7 to 8 cm from the midline could NOT correspond to the ligament attachment.
However, the ILIAC TRIGGER POINT corresponds with the position where the MEDIAL CUTANEOUS DORSAL RAMI or cluneal nerve (L1 or L2) cross the crest superficially on its dorsal aspect, the nerve becomes superficial by perforating the thoracolumbar fascia through a rigid osteomembranous orifice. The nature of this orifice leaves the nerve prone to irritation or compression.
Conclusion
They think that the ILIAC TRIGGER POINT situated at the level of the iliac crest, and 7 to 8 cm from the medial line, LIKELY CORRESPONDS to the presence of the nerve that can be compressed against the iliac crest palpation. This nerve could produce pain, either by referral from a facet syndrome or, secondary, to local compression or irritation.
Published in November 2018 by Marta Cañis Parera 
Some references:
-Maigne J. Y., Maigne R. Trigger Point of the Posterior Iliac Crest: Painful Iliolumbar Ligament Insertion or Cutaneous Dorsal Ramus Pain? An Anatomic Study. Arch Phys Med rehabll vol 72, September 1991.
-Hirscherberg G.G. et al. Iliolumbar Syndrome As a Common Cause of Low Back Pain: Diagnosis and Prognosis. Arch Phys Med rehabil 1979; 60:415-9.
-Maigne R. Low Back Pain of Thoracolumbar Origin. Arch Phys Med Rehabil 1980;61:389-95.
