For many years, I used to think low back pain is a muscle, spine, or pinched nerve problem. After reading about the history of pain science and the research about gate control theory and neuromatrix theory, low back pain is much more than just “something is wrong with my tissues.”

Although psychosocial factors can affect pain intensity and the perception of pain, low back pain can primarily be caused by biological factors, such as irritated or “entrapped” cluneal nerves.

What is cluneal nerve entrapment?

Entrapment of these cutaneous nerves of the buttocks was once described as the tendency for the cluneal nerves to get stuck where they pass through the fascia near the iliac crest.

However, Tubbs et al. stated that such entrapment is uncommon yet possible, and they did not find any “osteofibrous tunnels or obvious compression sites” that could cause these nerves to get “stuck” among 20 cadavers.

They suggested that more obvious and common causes of low back pain and leg pain should be ruled out before considering entrapped cluneal nerves be a possibility.

“We found no anatomical variation between sex, age or side,” lead author Dr. Shane Tubbs said in an online interview.

However, Aota cited a few studies that yielded some evidence that “suggested entrapment of the penetrating nerves within or under the ligament is a potential cause for [low back pain] and peripartum pelvic pain” because “primary and secondary loops of the posterior sacral nerve plexus passed through or underneath the LPSL.

It appears that this is quite a controversial topic, especially so little is known about cluneal nerves and their role in contributing to pain.

However, in cases where cluneal nerve entrapment is more likely, this condition makes up about 12 percent of reported chronic low back pain and half of this population reported leg pain as well.

Most of this entrapment — clunealgia — stem from the superior cluneal nerves (SCN), which pass between the iliac crest and lumbar of gluteal fascia attaching to the crest.

Medial cluneal nerves (MCN) are less likely to cause clunealgia because of their shorter length and course through multiple layers of fascia. Most physicians would diagnose clunealgia by palpation along the iliac crest or long posterior sacroiliac ligament under the patients responds to tenderness or pain relief after a local anesthetic injection.

Dr. Yoichi Aota, who is a physician and researcher at the Yokohama Brain & Spine Center in Yokohama, Japan, said, “SCN tender point was on the posterior iliac crest approximately 70 mm from the midline and 45 mm from the PSIS. The MCN tender point was on the LPSL within 40 mm caudal to the PSIS.”

However, these palpation methods are not very reliable because of how tiny the distances are and anatomical variations among different people.

Dr. Aota said in an online interview that very few doctors and surgeons know much about clunealgia or even the anatomy of cluneal nerves when he started to investigate this topic.

“I started this study about 12 years ago. At that time, literature in this topic is very limited. No information was available in the text book of orthopaedics and spine surgeries,” Aota said.

He mentioned that French surgeon Jean-Yves Maigne, who is one of early researchers in cluneal nerve’s contribution to back pain, had reported that SCN entrapment is a rare cause of low back pain. Contrarily, Aota finds that half of his patients have back and leg pain because of entrapped cluneal nerves.

“After having experienced SCN surgery, I found many patients have pain at MCN. I think that most of MCN entrapments were treated as sacroiliac joint problem because few doctors know MCN entrapment,” Aota said.

So he and a team of physicians, surgeons, and researchers at the clinic conducted a pretty large prospective study from 2009 to 2013 that included 834 patients with severe chronic low back pain and/or leg pain.

Only 113 of them were diagnosed with SCN pain. When less invasive treatments failed to reduce sufficient pain, surgery was performed on 19 patients to decompress the SCN and remove the SCN block.

The surgery had some success. Among 16 patients with leg pain, three had complete pain relief, two had almost complete relief, and three had no improvement. Among the eight remaining patients, they all had some pain relief within the six months of follow-up, and five of them had temporary relapse of pain post-surgery.

While not everyone had sufficient pain relief with surgery, Aota noted that more than three days of pain relief after blocks had better pain outcomes than those with less than three days of relief.

Aota isn’t the only one who thinks that this etiology is under-diagnosed. Dr. Shane Tubbs, who is the Chief Scientific Officer of Seattle Science Foundation in Seattle, Wash., said that the “prevalence of cluneal nerve entrapment is not known but is probably under-diagnosed due to a lack of awareness among medical practitioners.

“It is not known if cluneal nerve entrapment could be asymptomatic but probably not. As with any nerve, they do not like to be irritated and react accordingly,” Tubbs explained, “because most pain physicians and spine surgeons do not know much about it.”

Does cluneal nerve entrapment cause back pain and hip pain?

Aota: Since the cluneal nerve consists of superior, middle, and inferior cluneal nerves, the superior and middle cluneal nerves can be entrapped and cause repetitive friction of the nerves, causing low back pain and leg pain or tingling sensation.

And so, cluneal neuralgia can cause mainly low back pain. Leg pain and/or tingling often be associated. Patients with severe pain usually have low back pain radiating leg area and occasionally in the inguinal area. This may resemble hip pain. Clinically, repetitive cluneal nerve blocks do work well.

Do some people have entrapped cluneal nerves with NO pain?

Aota: Because I have seen only patients with pain, I do not know if some people have entrapped cluneal nerves with NO pain. If people do not have pain even with some degree of entrapment, these situations may be referred to as “entrapment without pain.”

Typical patients with mild entrapment have repetitive acute pain occurring several times per year. Pain usually is aggravated by movement. This would disturb exercise, such as playing golf. Some patients with chronic and severe entrapment have very severe leg pain lasting all day long radiating to the legs.

Tubbs: Bone grafting from the iliac crest is probably one of the most common reasons to injury these nerves, but other regional surgical procedures could do the same. As the cluneals all have an origin from the spinal nerves or their branches, spine operations could result in their injury.

What causes cluneal nerves to get “stuck?”

Aota: Superior cluneal nerve passes between the iliac crest and gluteal fascia attaching to the crest. Middle cluneal nerve passes  through a ligament around sacroiliac joint (long posterior sacroiliac ligament).

Because humans are bipedal and keep certain postures, such as flexion, posture increases loads in back and buttock muscles and long posterior sacroiliac ligament, which may make SCNs and MCNs to be at great risk of causing pain by irritating these areas.

Although young patients, like teenagers, sometimes have SCN pain, a majority of SCN and MCN patients are older than 50. That is why I believe that  aging is one of the contributing factors.

Spinal instability at thoraco-lumbar junction may initiate cluneal neuralgia because the SCN originates from this area. Spinal kyphosis following osteoporotic vertebral fractures may often aggravate cluneal neuralgia because the nerve is stretched by kyphosis.

What can physiotherapists and massage therapists do for patients with such pain?

Aota: Twelve years ago, many of such information was available from massage therapists or acupuncturists. I was interested to find that no doctors know about this clinical entity whereas many massage therapists knows this. Perhaps, this is because these therapists routinely touch patients. However, we (spine surgeons) do not know the tender points and never touch SCN or MCN points in the clinical situation.

During surgeries, I often observed adhesion around the nerves.  I believe that stretch exercise may prevent adhesion. However, when the pain is severe, exercise may aggravate the pain.

Why did you choose to do this research about cluneal nerves?

Aota: This is GREAT and THE MOST IMPORTANT QUESTION.

I started this study about nine years ago. At that time, literature in this topic is very limited. No information was available in the text book of orthopaedics and spine surgeries.

Surgical report was only by Maigne in France. Although Maigne reported, SCN entrapment as a rare cause of  low back pain, I found many patients in my clinic to have such pain. Moreover, half of my patients have not only low back pain but also leg pain.

Tubbs: Pain syndromes are a big problem, especially back pain. Sometimes, other pathologies in the area can result in pain that is referred to the back. One issue is cluneal nerve entrapment, which is scantly mentioned in the medical literature.

Is surgery the only way to alleviate pain?

Aota: Repetitive nerve blocks work well in the majority of patients. If pain is gone, I encourage patients to do some sports or exercise, such as yoga, to prevent adhesions as I stated above.

If blocks do not work well, I would select surgical release. As stated in the paper you read, new pain and longer pain relief  after nerve blocks are good candidates.  If pain remains or reappears, I recommend to use radio-frequency treatment therapy.

What do you think could manual therapists learn about cluneal nerve research?

Tubbs: Most professional anatomy course do not teach about the cluneal nerves. Even many medical curricula leave these out.

Therapists should be at least aware of these nerves as they will undoubtedly have patients with pain in their distribution and will probably be manually stimulating these branches during some of their treatments. This is not clear as the cluneal pain might be interpreted precisely or lumped together as “back pain.”

I’ve taught anatomy to just about every medical and medically related profession over the years and each want to emphasize various things, and this is usually mandated by a lack of time to cover everything.

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A native of San Diego for nearly 40 years, Nick Ng is an editor of Massage & Fitness Magazine, an online publication for manual therapists and the public who want to explore the science behind touch, pain, and exercise, and how to apply that in their hands-on practice or daily lives.

An alumni from San Diego State University with a B.A. in Graphic Communications, Nick also completed his massage therapy training at International Professional School of Bodywork in San Diego in 2014.

When he is not writing or reading, you would likely find him weightlifting at the gym, salsa dancing, or exploring new areas to walk and eat around Southern California.