Low back pain due to middle cluneal nerve entrapment neuropathy.

Purpose: The etiology of low back pain (LBP) is complicated and the diagnosis can be difficult. Superior cluneal nerve entrapment neuropathy (SCN-EN) is a known cause of LBP, although the middle cluneal nerve (MCN) can be implicated in the elicitation of LBP.

Methods: A 76-year-old woman with a 4-year history of severe LBP was admitted to our department in a wheelchair. She complained of bilateral LBP that was exacerbated by lumbar movement. Her pain was severe on the right side and she also suffered right leg pain and numbness. Based on palpation and nerve blocking findings we diagnosed SCN-EN and MCN entrapment neuropathy (MCN-EN).

Results: Her symptoms improved with repeated SCN and MCN blocking; the MCN block was the more effective and her symptoms improved. As her right-side pain around the MCN -EN with severe trigger pain recurred we performed microscopic right MCN neurolysis under local anesthesia. This led to dramatic improvement of her LBP and leg pain and the numbness improved. At the last follow-up, 7 months after surgery, she did not require pain medication.

Conclusions: The MCN consists of sensory branches from the dorsal rami of S1-S4. It sandwiches the sacral ligament between the posterior superior and inferior iliac spine as it courses over the iliac crest. Its entrapment at this hard orifice can lead to severe LBP with leg symptoms. An MCN block effect is diagnostically useful. Less invasive MCN neurolysis under local anesthesia is effective in patients who fail to respond to observation therapy.