Superior Cluneal Nerve Entrapment Syndrome

Superior Cluneal Nerve Entrapment Syndrome

Entrapment of the superior cluneal nerve is an uncommon cause of low back and buttocks pain. Comprising the terminal branches of the posterior rami of L1, L2, and L3 nerve roots, the superior cluneal nerves provide cutaneous innervation to the upper part of the buttocks and are susceptible to entrapment as they pass over the iliac crest through a tunnel formed by the thoracolumbar fascia and the superior rim of the iliac crest in a manner analogous to compression of the median nerve as it passes through the carpal tunnel. The middle branch is most commonly affected.

This entrapment neuropathy presents as pain, numbness, and dysesthesias in the distribution of the superior cluneal nerve. The symptoms often begin as a burning pain in the upper buttocks with associated cutaneous sensitivity. Patients with superior cluneal nerve entrapment note that sitting, squatting, or wearing tight jeans with a low rise causes the symptoms to worsen. Although traumatic lesions to the superior cluneal nerve during bone harvesting procedures and pelvic fractures have been implicated in superior cluneal nerve entrapment, in most patients, no obvious antecedent trauma can be identified.

What are the Symptoms of Superior Cluneal Nerve Entrapment Syndrome

Physical findings include tenderness over the superior cluneal nerves as they pass over the posterior iliac crest. A positive Tinel sign over the superior cluneal nerves as they pass over the posterior iliac crest may be present. Patients may report burning dysesthesias in the nerve’s distribution. Careful sensory examination of the upper buttocks may reveal a sensory deficit in the distribution of the superior cluneal nerves; no motor deficit should be present. Sitting or the wearing of low-cut jeans with tight waistbands or wide belts can compress the nerve and exacerbate the symptoms of superior cluneal nerve entrapment.

How is Superior Cluneal Nerve Entrapment Syndrome diagnosed?

Electromyography can distinguish lumbar radiculopathy and plexopathy from superior cluneal nerve entrapment. Plain radiographs of the back, hip, and pelvis are indicated in all patients who present with superior cluneal nerve entrapment to rule out occult bony pathological processes.

Based on the patient’s clinical presentation, additional testing may be warranted, including a complete blood count, uric acid level, erythrocyte sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging (MRI) of the back is indicated if herniated disk, spinal stenosis, or space-occupying lesion is suspected and to further clarify the diagnosis. Ultrasound imaging may help identify nerve entrapment. The injection technique described later serves as both a diagnostic and therapeutic maneuver.

Differential Diagnosis

Superior cluneal nerve entrapment is often misdiagnosed as lumbar radiculopathy, sacroiliac joint pain, gluteal bursitis, or primary hip pathological conditions. Radiographs of the hip and electromyography can distinguish superior cluneal nerve entrapment from radiculopathy or pain emanating from the hip. In addition, most patients with lumbar radiculopathy have back pain associated with reflex, motor, and sensory changes, whereas patients with superior cluneal nerve entrapment have no back pain and no motor or reflex changes.

The sensory changes of superior cluneal nerve entrapment are limited to the distribution of the superior cluneal nerve and should not extend below the upper buttocks. It should be remembered that lumbar radiculopathy and superior cluneal nerve entrapment may coexist as the “double crush” syndrome. Occasionally, lumbar plexopathy produces buttocks pain, which may confuse the diagnosis.

Treatment

Patients with superior cluneal nerve entrapment should be instructed in avoidance techniques to reduce the symptoms and pain associated with this entrapment neuropathy. A short course of conservative therapy consisting of simple analgesics, nonsteroidal antiinflammatory drugs (NSAIDs), or cyclooxygenase-2 (COX-2) inhibitors is a reasonable first step in the treatment of superior cluneal nerve entrapment. If patients do not experience rapid improvement, injection is the next step.

To treat the pain of superior cluneal nerve entrapment, the patient is placed in the prone position. The posterior iliac crest is identified by palpation, as are the spinous processes of the adjacent lumbar vertebrae. A point 7 cm lateral to midline along the posterior iliac crest is identified and prepared with antiseptic solution.

A 1½-inch, 25-gauge needle is slowly advanced perpendicular to the skin until the needle is felt to pop through the fascia. A paresthesia is often elicited. After careful aspiration, a solution of 5 to 7 mL of 1% preservative-free lidocaine and 40 mg methylprednisolone is injected in a fanlike pattern as the needle pierces the fascia gluteal muscle. After injection of the solution, pressure is applied to the injection site to decrease the incidence of ecchymosis and hematoma formation, which can be quite dramatic, especially in anticoagulated patients.

If anatomical landmarks are difficult to identify, the use of fluoroscopic or ultrasound guidance should be considered to improve the accuracy of needle placement and decrease the incidence of needle-related complications.

Complications

Care must be taken to rule out other conditions that may mimic the pain of superior cluneal nerve entrapment. The main complications of the injection technique are ecchymosis and hematoma. Rarely, infection may occur. Early detection of infection is crucial to avoid potentially life-threatening sequelae.

Clinical Pearls

Superior cluneal nerve entrapment is a common condition that is often misdiagnosed as lumbar radiculopathy, sacroiliac pain, or gluteal bursitis.

The injection technique described can produce dramatic pain relief; however, if a patient has pain suggestive of superior cluneal nerve entrapment but does not respond to superior cluneal nerve block, a lesion more proximal in the lumbar plexus or an L1–L3 radiculopathy should be considered.

Such patients often respond to epidural block with steroid. Electromyography and MRI of the lumbar plexus are indicated in this patient population to rule out other causes of pain, including malignancy invading the lumbar plexus or epidural or vertebral metastatic disease at L1–L3.


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