PM&R News   •   August 2019

The superior and middle cluneal nerves are cutaneous nerves which are purely sensory and provide most of the sensation to the low back and buttocks. The most common site of entrapment is around the iliac crest. Cluneal nerve entrapment can produce symptoms of low back pain, leg pain, and groin pain. These symptoms are often exacerbated by lumbar movements, and mimic radiculopathies. Superior cluneal nerve entrapment (SCN-E) can also cause intermittent claudication. Identification of the trigger point at the site of entrapment, and subsequent resolution of symptoms after a nerve block is diagnostic of entrapment. Complaints of low back pain are common, and the etiologies are numerous. Cluneal nerve entrapments must be routinely considered in the differential diagnosis to assure thorough evaluation and avoidance of unnecessary invasive procedures.

The incidence of SCN-E in low back pain is 14%, females comprised 55-63% of patients, and the average age of onset is 55-68 years old.¹ The true incidence of middle cluneal nerve entrapment (MCN-E) is unknown. The SCN originates at the lower thoracic and lumbar posterior nerve root. At the iliac crest, it penetrates the thoracolumbar fascia. The medial branch penetrates the fascia 3–4 cm from the midline, and the middle branch 7–8 cm from the midline. A portion of the SCN passes through the osteofibrous tunnel formed by the thoracolumbar fascia and the iliac crest. Entrapment at that site results in low back pain. The MCN originates at S1–S4. It sandwiches the long posterior sacroiliac ligament (LPSL) between the posterior superior iliac spine (PSIS) and the posterior inferior iliac spine (PIIS). It then passes over the iliac crest to the buttocks. The site of MCN-E is where the lateral branches of the dorsal sacral rami penetrate the LPSL.

The SCN and MCN are both very thin (1-3 mm) making correct identification of symptoms vital as both nerves will be difficult to identify on either CT or MRI. When SCN or MCN entrapment is suspected the presences of a Tinel-like sign at the trigger point is partially diagnostic. For SCN-E the trigger point is at the site where the SCN passes over the iliac crest at either 3-4 cm or 7-8 cm from the midline. For MCN-E the trigger point is where the MCN passes over the LPSL between the PSIS and the PIIS on the edge of the iliac crest.

There are many treatment modalities both surgical and non-surgical. For non-surgical therapies a nerve block may be considered which is further diagnostic of SCN-E or MCN-E.² Other non-surgical interventions include the use of hydrodissection, and radiofrequency ablation. Cluneal nerve entrapment is not a rare cause of low back pain, and should be considered in the differential. Consideration of these as potential causes of low back pain can provide patients with an effective non-surgical intervention and relief from pain.

Contributing Author:  Zakari Dymock, MD