Middle cluneal nerve entrapment sites in the surgical field

Middle cluneal nerve (MCN) entrapment around the sacroiliac joint elicits low back pain (LBP). For surgical decompression to be successful, the course of the MCN must be known. We retrospectively studied the MCN course in 15 patients who had undergone MCN neurolysis.

Enrolled in this retrospective study were 15 patients (18 sides). We inspected their surgical records and videos to determine the course of the entrapped MCN. The area between the posterior superior- and the posterior inferior iliac spine was divided into areas A-D from the rostral side. The MCN transit points were identified at the midline and the lateral edge connecting the posterior superior- and posterior inferior iliac spine. Before and 6 months after surgery, the patients recorded the degree of LBP on the numerical rating scale and the Roland-Morris Disability Questionnaire.

We decompressed 24 MCNs. The mean number was 1.3 nerves per patient (range 1-2). The MCN course was oblique in the cranio-caudal direction; the nerve tended to be observed in areas C and D. In six patients (40%), we detected two MCN branches, they were in the same area and adjacent. Postoperatively, LBP was improved significantly in all patients.

Between the posterior superior- and the posterior inferior iliac spine, the MCN ran obliquely in the cranio-caudal direction; it was prominent in areas on the caudal side. In six (40%) patients, we decompressed two adjacent MCNs. Our findings are useful for MCN decompression surgery.