Konno et al. carried out a laboratory investigation with 23 cadaveric dissections to explain how the superior cluneal nerve entrapment can cause pseudo-sciatica (not just low back pain).

The authors emphasize the importance of identifying SCNs passing through an osteofibrous tunnel because these branches have a higher risk of entrapment (sometimes the nerves originate from L4 and L5, not just from L1- to L3 -as was previously described in classical books-). Konno et al indicated that the L4 and L5 lateral branches that pass through the osteofibrous tunnel in the fascia overlying the iliac crest had more risk of entrapment.

They performed cadaveric dissections. Their study is divided into two parts, the recognition of the levels of lumbar nerve root originating SCN branches and measurements of the distances from anatomical landmarks and diameter of SCN.

Notes on the article of:

Anatomical etiology of “pseudo-sciatica” from superior cluneal nerve entrapment: a laboratory investigation

Konno T., Aota Y., Kuniya H., Saito T., Qu N., Hayashi S., Kawata S., Itoh M.

Journal of Pain Research 2017; (10): 2539-3545

From the Department of Orthopaedic Surgery, Yokohama City University and Department of Spine & Spinal Cord Surgery, Yokohama Brain and Spine Center, Yokohama, Japan.

The Superior Cluneal Nerve (SCN) entrapment cause low back pain and pseudo-sciatica

According to Konno et al., the SCN is a cutaneous branch of the lumbar dorsal that penetrates the psoas major and paraspinal muscles. When the medial SCN branch penetrates the gluteal fascia, the nerve becomes entrapped in the osteofibrous tunnel (space surrounded by the iliac crest and the fascia attached to the iliac crest), this may produce low back pain (LBP) often with referred pain in various areas of the leg, producing the condition also known as pseudo-sciatica.

The main weakness of the previous anatomical studies is that they do not explain how SCN entrapment produces pseudo-sciatica (specially because traditionally the anatomy books mention that SCN arise form the levels L1, L2 and L3), Konno et al raise this issue through of anatomical study listed below:

The main objective of this study is to identify SCNs at risk of entrapment and their origin from nerve roots.
SCN branches were dissected from their origin to termination in subcutaneous tissue in 16 cadavers with a total of 23 sides (a mean death of 88 years).
Particular attention was paid to the observation of a constriction of the SCN branch in the osteofibrous tunnel.

The anatomical study by Konno et al. Focuss in two parts

Their anatomical study consists of two parts:
Identification of the levels of lumbar nerve root originating SCN branches, here the number of SCN branches was counted where they pass over the iliac crest and each nerve root was identified concerning lumbosacral junction and/or the 12^th rib.
Measurements of the diameter of SCNs and linear distances from the midline and the posterior superior ilac spine (PSIS) to the SCN branches over the iliac crest, a digital calipter was used.

Figure 1: SCN branches on the left side from the cadaver of a 90-year-old woman.

Figure 2: SCN branches on the right side from the cadaver of an 89-year-old man, specimen no. 22. In this case, the L5 nerve roots had a dorsal branch ramifying into a1 and a2 SCN branches (Konno et al, 2017).

Konno et al. results to explain pseudo-sciatica

The anatomical findings of this paper are summarized below:

SCN branches identified: 81 on the 23 examined sides, originated from T12 to L5 nerve roots.

SCN branches passed through the osteofibrous tunnel: 13 originated from L3 (two sides), L4 (six sides) and L5 (5 sides) nerve roots.
SCN branches had entrapment (Figure 3): 10 of 13 (76.92%), of these 10 branches entrapped in the tunnel, seven nerves were the most medial branch originating from L4 and L5, two were the second most medial branch from L3 and L4, and one was the third most medial branch from L3.

Figure 3: Entrapment of the second most medial branch of the SCN in cadaveric specimen no.23

Regarding the anatomical measurements the following information is reported:

The mean distance from the midline to the SCN branches passing through the osteofibrous tunnel was 66.1 mm.
The mean linear distance from the PSIS to the SCN branches passing through the osteofibrous tunnel was 40.8 mm.
The diameter of the SCNs ranged from 0.3 to 2.9 mm.

Notes about the discussion how superior cluneal nerve entrapment can presented as pseudo-sciatica

Differences and similarities between previous studies and the outcomes obtained by Konno et al are summarized below:

Earlier works as (Berthelot et al, 1996), (Lu et al, 1998) found that three SCN branches pass over the iliac crest. By contrast, in this paper is demonstrated that 8 of 23 sides (35%) had more than three branches passing over the iliac crest.
Previous anatomical studies reported that SCN branches arise from the thoraco-lumbar junction or upper lumbar levels (L1,L2,L3). This research underlined that the SCNs arising from T12 to L5 nerves roots according to their case of study.
According to the outcomes of the present study, the majority of SCNs at risk of nerve entrapment originated from the lower lumbar nerve. Konno et al indicated that the L4 and L5 lateral branches pass through the osteofibrous tunnel in the fascia overlying the iliac crest and had more risk of entrapment.
Regarding the proportion of entrapment of the SCN in the osteofibrous tunnel, the authors point out that their study differs considerably from that the previous literature, for example, they found 30% or 7/23 specimens with entrapment compared to the information reported by (Maigne et al, 1989) 5% or 2/37.
In conclusion, these findings showed evidence of how SCN entrapment disorder causes leg symptoms or tingling that mimics sciatica, also called pseuo-sciatica.

Some references

Aota Y. Entrapment of middle cluneal nerves as an unknown cause of low back pain. World J Orthop. 2016;7(3):167–170.

Berthelot JM, Delecrin J, Maugars Y, Caillon F, Prost A. A potentially underrecognized and treatable cause of chronic back pain: entrapment neuropathy of the cluneal nerves. J Rheumatol. 1996;23(12):2179–2181.

Kuniya H, Aota Y, Kawai T, Kaneko K, Konno T, Saito T. Prospective study of superior cluneal nerve disorder as a potential cause of low back pain and leg symptoms. J Orthop Surg Res. 2014;9:139.

Kuniya H, Aota Y, Saito T, et al. Anatomical study of superior cluneal nerve entrapment. J Neurosurg Spine. 2013;19(1):76–80.

Lu J, Ebraheim NA, Huntoon M, Heck BE, Yeasting RA. Anatomic considerations of superior cluneal nerve at posterior iliac crest region. Clin Orthop Relat Res. 1998(347):224–228.

Maigne JY, Lazareth JP, Guerin Surville H, Maigne R. The lateral cutaneous branches of the dorsal rami of the thoraco-lumbar junction. An anatomical study on 37 dissections. Surg Radiol Anatomy. 1989;11(4):289–293.

Abbreviations

a1, a2, a3, a4, a5: Superior cluneal nerve branches

L1, L2, L3, L4, L5: Lumbar vertebraes

PSI: Posterior superior ilac spine

T12: Thoracic vertebraes

SCN: Superior cluneal nerve

Published by Marta Cañis Parera in January 2020 (with the collaboration from Mauricio Valarezo).