INTRODUCTION: The superior cluneal nerve (SCN) becomes superficial by passing through the thoracolumbar fascia. Previous anatomical studies have indicated that branches of the SCN pass through the fascia below the iliac crest. Maigne reported on entrapment of the medial branch of the SCN in the space between the iliac crest and the fascia (the osteofibrous orifice or tunnel) as a cause of low back pain (Surg Radiol Anat. 1989). In their subsequent surgical study, successful results were obtained even when severe entrapment was observed during surgery (Spine. 1997). The purpose of this study was to investigate the running courses of the branches of the SCN over the iliac crest and to ascertain the frequency of SCN entrapment in the osteofibrous tunnel.
METHODS: The medial, intermediate and lateral branches of the SCN were dissected in 89 investigable specimens from 49 formalin‐preserved cadavers (22 male and 27 female; average age at death 84.2 years; range 67‐103 years). All branches of the SCN were exposed at the points where they perforated the fascia. The presence or absence of an osteofibrous tunnel in their running courses was recorded.
RESULTS: Forty‐two of the 89 specimens had no osteofibrous tunnel (47.2%). The other 47 had at least one branch running through an osteofibrous tunnel. Thirtythree out of 89 medial SCN branches (37.1%), 23 intermediate branches (25.8%) and 7 lateral branches (7.9%) passed through an osteofibrous tunnel. Severe entrapment in the osteofibrous tunnel was observed in only two specimens, both in the medial branch.
DISCUSSION: Although Maigne noted that only the medial branch of the SCN passed through an osteofibrous tunnel, we found that not only the medial, but also other branches of the SCN became superficial by passing over the iliac crest through an osteofibrous tunnel. The incidence of entrapment in osteofibrous tunnels was 3.2%.