Superior Cluneal Nerve Entrapment
|Superior Cluneal Nerve Entrapment|
|Name||Cluneal nerve pain|
|Synonym||Cluneal nerve entrapment, cluneal neuralgia, clunealgia|
|Epidemiology||14% of CLBP (SCN entrapment), MCN entrapment may be rare.|
|Pathophysiology||Repetitive friction of SCN under the thoracolumbar fascia, or rarely constriction in the osteofibrous tunnel.|
|Risk Factors||Thoracolumbar site fractures at the origin of the SCN|
|Diagnosis||focal iliac crest tenderness, reproduction of symptoms with pressure, and pain reduction with block.|
|DDX||Sacroiliac joint pain, referred lumbar spine pain|
|Treatment||Repeated local anaesthetic injections, SCN or MCN decompression|
The cluneal nerves are a group of pure sensory nerves (superior, medial or middle, and inferior) that provide sensory supply to the buttocks. There is some evidence that superior cluneal nerve entrapment, also known as cluneal neuralgia, or clunealgia, is an under-diagnosed cause of chronic low back and leg pain. See also the less common middle cluneal nerve entrapment and inferior cluneal nerve entrapment.
A good retrospective study was done by Kuniya et al who systematically evaluated 834 patients with CLBP; the article is open access and a highly recommended read. Their team has published other recent literature on the topic. A recent open access review article on SCN and MCN entrapment was authored by Isu et al.
The cluneal nerves are divided into the superior cluneal nerve (SCN), middle cluneal nerve (MCN), and inferior cluneal nerve (ICN).
The cutaneous nerve supply of the upper back is supplied by the medial branches of the upper thoracic dorsal rami, while the lower back is supplied by the lateral branches of the lower thoracic and upper lumbar dorsal rami. These are called the superior cluneal nerves, and are composed of the lateral cutaneous branches of the dorsal rami of T11-L4 (some authors state T12-L3 or L1-3). There is variability in which of the lateral branches become cutaneous. In embryos and fetuses L1 is always cutaneous, L2 in 90%, L3 in 70%, and L4 in 40%. In adults it is similar except L4 cutaneous branches are uncommon. In 37 dissections, the low back was innervated by the lateral branches of the dorsal rami of T12 and L1 in 60% of cases, T12-L2 in 27% of cases, and T12-L3 in 13% of cases (L1 and L2 receiving an anastomosis from L3).
The lateral branches emerge from the dorsolateral border of iliocostalis lumborum, become cutaneous, pierce the thoracolumbar fascia, and descend inferolaterally across the iliac crest to innervate the posterior iliac crest and superomedial gluteus maximus. When crossing the iliac crest they run parallel to one another with those from lower levels lying most medially. These different branches are called the medial branches (mSCN), intermediate or middle branches (iSCN), and lateral branches (lSCN). Do not confuse the middle and medial SCN branches with the middle cluneal nerve (MCN).
The lowest and most medial nerve (mSCN) arises from the deep fascia and crosses the iliac crest approximately 7-8cm from the midline. The mSCN often passes through an osseofibrous tunnel made up of the thoracolumbar fascia and the PSIS. There is significant anatomical variation. In a cadaver study of 109 medial branches, 39% passed through and osseofibrous tunnel, and of these only 5% exhibited obvious entrapment, or 2% of the total dissected branches.
Cluneal nerve irritation may arise due to entrapment in fascia or from nerve root irritation in the epidural space or foramen. Fascial entrapment may be a self-perpetuating process. Pain may occur following spinal fusion, sacroiliac screw placement, sacral ulcer debridement, muscle flap surgeries, iliac bone harvesting, trauma, muscle spasm, spinal canal stenosis, disc herniation, scoliosis, vertebral fractures, and Parkinson's disease. 
Superior cluneal nerve (SCN) entrapment is thought to occur where the nerve pierces the thoracolumbar attachment at the posterior iliac crest as it becomes superficial. Typically it has been described based on cadaver studies that the medial branch of the SCN passes through an osteofibrous tunnel and can be spontaneously entrapped there.
However, Kuniya et al found that in their 19 subjects requiring SCN release there were no cases of severe constriction within a bony groove on the iliac crest, but they found at least two SCN branches passing underneath a mixture of superficial thoracolumbar and gluteal fascia at the point of attachment to the iliac crest. They posited that true construction in the osteofibrous tunnel was rare, and that severe symptoms may be due to repetitive friction of the SCN under the fascia. In a further unpublished 26 cases, they had two cases of fascial constriction over the ilium.
The prevalence of vertebral compression fractures is higher in those with SCN entrapment than in those without a SCN disorder (26% vs 12%), most commonly at T12-L3. It is theorised that this causes a sagittal imbalance with increased kyphosis of the spine, thereby irritating the SCN at its origin from unstable facet joints or by stretching the SCN itself. Maigne described thoracolumbar syndrome, whereby thoracolumbar dysfunction causes one of or a combination of unilateral iliac crest pain, lateral hip pain, and groin pain. Knight et al hypothesises that pelvic malrotation and loss of sagittal balance may be an important aetiological factor, even without vertebral fracture and irritant angulation of the cluneal nerve pathway. 
In one retrospective review of 834 patient with low back pain, 14% were thought to be due to superior cluneal nerve entrapment. However this diagnosis was made clinically (see the diagnostic method in the diagnosis section below). 62% of the clinically diagnosed patients had a 50% decreased in VAS or more. This would give a prevalence of ~8% if only including those with one or more positive injections. It is more common in middle age. Male and female distributions are roughly equal. 
The cardinal symptom is chronic low back pain with or without leg symptoms. Knight et al believe that pelvic malalignment may be a relevant finding with pelvic anterior anteversion, and this may explain why transitional movements can be painful. Cluneal nerve pathology may exist in tandem with other spinal pathology. Symptoms may mimic sciatica. Symptoms may have a neuropathic quality.
In those with a SCN disorder, around 50% have leg symptoms, but only 1% have leg symptoms only. The most commonly aggravating features are walking, rising from sitting, standing, flexion, and extension. Patients often find that pushing above the iliac crest with their hands relieves symptoms. Some patients have claudication like symptoms. The pain can persist for many years and some patients can be severely disabled.
For medial branch SCN pain, there should be maximal tenderness over the PSIS approximately 70mm from the midline and 45mm from the PSIS. coupling rotation to contralateral side and flexion can aggravate symptoms. As can flexion and contralateral rotation. Ipsilateral hip extension may reduce pain during flexion.  The medial SCN branches may pass around a small palpable lipoma.
For the lateral nerve group there may be tenderness near the mid-point of the iliac crest, lateral to the tubercle. They tend to be more variable in location and therefore point of irritation.
- Figure: Cluneal nerve pain distribution.
There is no agreed diagnostic method. The diagnosis can be considered by tenderness over the iliac crest causing provocation of symptoms. Pain relief following local anaesthetic injection can give further weight to the diagnosis.
Kuniya et al used the following diagnostic criteria 
- Maximal tenderness over the posterior iliac crest approximately 70 mm from the midline and 45 mm from the PSIS where the medial branch of the SCN runs through an osteofibrous tunnel consisting of the thoraco-lumbar fascia and the iliac crest (even if lesser tenderness exists elsewhere, for example at the thoracolumbar junction).
- Palpation of the maximally tender point reproduced the chief complaint of LBP and/or leg symptoms (Tinel-like sign)
- Temporary relief of symptoms by local anaesthetic injection
In their study, patients were included when they met the first two criteria. A nerve block injection was performed. If relief of symptoms is obtained following injection they suggest that this gives further weight to the diagnosis. In their study, if repeated injections failed to relieve symptoms then they had SCN decompression.
Mechanical Low Back or Leg Pain (97%)
- Discogenic pain
- Internal disc disruption (subset of discogenic pain)
- Facet joint pain
- Sacroiliac joint or ligament pain
- Vertebrogenic (e.g. modic changes on MRI)
- Spinal stenosis
- Abnormal motion/instability
- Myofascial syndrome
- Cluneal nerve entrapment
- Osteoporotic compression fracture and other fractures
- Spondylolisthesis and spondylolysis
- Transitional vertebrae
- Presumed instability
- Interspinous oedema/bursitis
- Back mice
Nonmechanical Spine Conditions (1%)
- Neoplasia (Multiple myeloma, metastatic carcinoma, lymphoma, leukaemia, spinal cord tumours, retroperitoneal tumours, primary vertebral tumours)
- Infection (Osteomyelitis, discitis, paraspinous abscess, epidural abscess, shingles)
- Inflammatory arthritis (Ankylosing spondylitis, reiter syndrome, inflammatory bowel disease)
- Scheuermann disease (osteochondrosis)
- Paget disease
Visceral Disease (2%)
- Pelvic organ involvement (Prostatitis, endometriosis, chronic pelvic inflammatory disease)
- Renal involvement (Nephrolithiasis, pyelonephritis, perinephric abscess)
- Aortic aneurysm
- Gastrointestinal involvement (Pancreatitis, cholecystitis, ulcer)
Manual and Physical Therapy
Maigne would treat thoracolumbar syndrome with manipulation. Others have used pelvic mobilisation and pelvic realignment. Pelvic malalignment may be well-established and difficult to reverse, and Muscle Balance Therapy or Reformer Pilates could be considered.
- Main article: Superior Cluneal Nerve Injection
Trigger point injections have been described, normally with plain local anaesthetic, but it can be done with additional steroid or as dextrose prolotherapy. In Kuniya et al's study using the diagnostic criteria above, 47% required a second local anaesthetic injection, and 25% required a third injection. In those who met the first two diagnostic criteria, 62% of patients had a 50% decrease of VAS after the first injection, 67% after the second injection, and 68% after the third injection.
There is very rare risk of erectile dysfunction following injections to the SCN.
An ultrasound guided injection technique is shown here
Radiofrequency neurotomy has also been described 
Reports have been published on SCN release. In Kuniya's study, approximately 20% of patients proceeded to SCN decompression due to failure of having long term relief from repeated SCN nerve blocks. Predictors of success were pain duration less than 3 years, and consistently having relief for three days or more from SCN blocks. Long term outcomes are satisfactory.
- Kuniya et al.. Prospective study of superior cluneal nerve disorder as a potential cause of low back pain and leg symptoms. Journal of orthopaedic surgery and research 2014. 9:139. PMID: 25551470. DOI. Full Text.
- Isu et al.. Superior and Middle Cluneal Nerve Entrapment as a Cause of Low Back Pain. Neurospine 2018. 15:25-32. PMID: 29656623. DOI. Full Text.
- Trescot, Andrea. Peripheral nerve entrapments : clinical diagnosis and management. Switzerland: Springer, 2016.
- Bogduk, Nikolai. Clinical and radiological anatomy of the lumbar spine. Edinburgh: Elsevier/Churchill Livingstone, 2012.
- Maigne et al.. The lateral cutaneous branches of the dorsal rami of the thoraco-lumbar junction. An anatomical study on 37 dissections. Surgical and radiologic anatomy : SRA 1989. 11:289-93. PMID: 2533408. DOI.
- Karri et al.. Pain Syndromes Secondary to Cluneal Nerve Entrapment. Current pain and headache reports 2020. 24:61. PMID: 32821979. DOI.
- Kuniya et al.. Anatomical study of superior cluneal nerve entrapment. Journal of neurosurgery. Spine 2013. 19:76-80. PMID: 23641672. DOI.
- Aota. Entrapment of middle cluneal nerves as an unknown cause of low back pain. World journal of orthopedics 2016. 7:167-70. PMID: 27004164. DOI. Full Text.
- Martin Knight., et al. “A Radiofrequency Treatment Pathway for Cluneal Nerve Disorders”. EC Orthopaedics 11.3 (2020): 01-19 Full Text
- Morimoto et al.. Long-term Outcome of Surgical Treatment for Superior Cluneal Nerve Entrapment Neuropathy. Spine 2017. 42:783-788. PMID: 27669049. DOI.