Anatomical study of superior cluneal nerve entrapment

J Neurosurg Spine 19:76–80, 2013 ©AANS, 2013

Anatomical study of superior cluneal nerve entrapment Laboratory investigation Hiroshi Kuniya, M.D.,1 Yoichi Aota, M.D.,1 Tomoyuki Saito, M.D.,1 Yoshinori Kamiya, M.D., 2 Kengo Funakoshi, M.D., 2 Hayato Terayama, Ph.D., 3 and Masahiro Itoh, M.D. 3 Departments of 1Orthopaedic Surgery and 2Neuroanatomy, Yokohama City University Graduate School of Medicine, Yokohama, Kanagawa; and 3Department of Anatomy, Tokyo Medical University, Shinjyuku, Tokyo, Japan Object. Entrapment of the superior cluneal nerve (SCN) in an osteofibrous tunnel in the space surrounded by the iliac crest and the thoracolumbar fascia is a cause of low-back pain (LBP). Several anatomical and surgical reports describe SCN entrapment as a cause of LBP, and a recent clinical study reported that patients with suspected SCN disorder constitute approximately 10% of the patients suffering from LBP and/or leg symptoms. However, a detailed anatomical study of SCN entrapment is rare. The purpose of this study was to investigate the courses of SCN branches and to ascertain the frequency of SCN entrapment. Methods. Branches of the SCN were dissected in 109 usable specimens (54 on the right side and 55 on the left side) obtained in 59 formalin-preserved cadavers (average age at death 84.8 years old). All branches were exposed at the points where they perforated the thoracolumbar fascia. The presence or absence of an osteofibrous tunnel was ascertained and, if present, the entrapment of the branches in the tunnel was determined. Results. Of 109 specimens, 61 (56%) had at least 1 branch running through an osteofibrous tunnel. Forty-two medial (39%), 30 intermediate (28%), and 14 lateral (13%) SCN branches passed through such a tunnel. Of these, only 2 medial branches had obvious entrapment in an osteofibrous tunnel. There were several patterns for the SCN course through the tunnel: medial branch only (n = 25), intermediate branch only (n = 11), lateral branch only (n = 4), medial and intermediate branches (n = 11), medial and lateral branches (n = 2), intermediate and lateral branches (n = 4), and all branches (n = 4). Conclusions. Several anatomical variations of the running patterns of SCN branches were detected. Entrapment was seen only in the medial branches. Although obvious entrapment of the SCN is rare, it may cause LBP. (http://thejns.org/doi/abs/10.3171/2013.4.SPINE12683)

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Key Words • low-back pain • superior cluneal nerve • osteofibrous tunnel • entrapment neuropathy

SCN comprises the cutaneous branches of the dorsal rami of T11–L4.1,11,13 It becomes superficial by passing through the thoracolumbar fascia above or below the iliac crest. Previous anatomical and clinical studies have described entrapment of the medial branch of the SCN in an osteofibrous tunnel in the space surrounded by the iliac crest and the thoracolumbar fascia as a possible cause of LBP.2,3,6,11,13,14,17,18 Trescot20 stated that cluneal neuralgia was more commonly the result of a spontaneous entrapment of the nerve than a nerve injury during bone harvest. Recently, Kuniya et al.9 reported that patients who met their stringent diagnostic criteria for SCN entrapment (maximal point tenderness at the osteofibrous tunnel and palpation of the tender point reproducing the chief complaint of LBP and/or leg symptoms) consisted of 24 (12%) of 207 consecutive patients visiting the spine clinic of their institute. Interestingly, these patients were more significantly disabled compared with he

Abbreviations used in this paper: LBP = low-back pain; SCN = superior cluneal nerve.

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others; the mean Roland-Morris Disability Questionnaire scores were 13.8 and 10.7, respectively. However, although there are few surgical reports of SCN entrapment, successful surgical outcomes were reported after exploration of the SCN, especially when severe entrapment was observed during surgery.6,12,17 In anatomical studies, controversy exists as to whether the medial branch of the SCN passes through an osteofibrous tunnel. Some anatomical studies have noted that all of the branches of the SCN pierced the thoracolumbar fascia above the iliac crest.1,4,5,7,8,10,15,20 In contrast, Maigne and colleagues,13,14 Lu et al.,11 and Xu et al.22 reported that all medial branches passed through an osteofibrous tunnel, whereas Moro et al.16 reported that 80% and Yazaki et al.23 that 95% of the medial branches passed through an osteofibrous tunnel. The purpose of this study was to investigate, using a relatively large number of cadaveric specimens, the This article contains some figures that are displayed in color online but in black-and-white in the print edition.

J Neurosurg: Spine / Volume 19 / July 2013

Superior cluneal nerve entrapment courses of the branches of the SCN over the iliac crest and to ascertain the frequency of SCN entrapment in an osteofibrous tunnel. In our study, intermediate and lateral branches of the SCN were also examined for their location over the iliac crest as well as for entrapment. The anatomical data of the location of the SCN branches over the iliac crest may provide valuable information to spine surgeons who are considering harvesting iliac crest bone.

Methods

The medial, intermediate, and lateral branches of the SCN were dissected in 109 usable specimens obtained in 59 formalin-preserved Japanese cadavers (27 male and 32 female; average age at death was 84.8 years old; age range was 67–103 years old). Their mean height was 147.9 cm (range 132.0–170.0 cm). Bilateral branches of the SCN were observed macroscopically. Nine of the 118 specimens that could not be observed in detail were excluded, and the remaining 109 specimens were used for this study. All branches of the SCN were exposed at the points where they perforated the thoracolumbar fascia. Linear distances from the midline and the posterior superior iliac spine to the branches of the SCN over the iliac crest were measured (Fig. 1). The specific parameters examined were the presence or absence of an osteofibrous tunnel in the course of the nerve and, if a tunnel was present, its length and the entrapment of the branches of the SCN in the tunnel. The osteofibrous tunnel was defined as the space surrounded by the iliac crest and the thoracolumbar fascia when the branches of the SCN pierced the thoracolumbar fascia below the iliac crest. Measurements were made using a Digimatic caliper (Mitsutoyo Corp.). Comparisons between groups were made using the Student t-test and ANOVA. The level of significance was defined as 0.05. Analyses were performed with Statcel 2 statistical software, version 2 (OMS Inc.).

Results

Of the 109 specimens, in 48 (44%) all 3 branches of the SCN passed through the thoracolumbar fascia above the iliac crest. In the remaining 61 specimens (56%), at least 1 branch of the SCN ran through an osteofibrous tunnel. Of 109 SCNs, 42 medial branches (39%), 30 intermediate branches (28%), and 14 lateral branches (13%) passed through an osteofibrous tunnel. There were several patterns for the course of the SCN through the osteofibrous tunnel: the medial branch only (n = 25), the inter-

Fig. 1. Schematic illustration of measurements for linear distances from the midline (distance a) and the posterior superior iliac spine (distance b) to a branch of the SCN coursing over the iliac crest in a specimen in which the medial branch of the right SCN runs through an osteofibrous tunnel (black semicylindrical area).

mediate branch only (n = 11), the lateral branch only (n = 4), medial and intermediate branches (n = 11), medial and lateral branches (n = 2), intermediate and lateral branches (n = 4), and all branches (n = 4). No branches pierced the same orifice of the fascia (Fig. 2). The linear distances from the midline to the medial, intermediate, and lateral branches were 71.0 ± 7.9 mm (50.0–87.5 mm), 76.7 ± 7.6 mm (52.6–93.3 mm), and 82.6 ± 8.2 mm (55.2–106.0 mm), respectively. The linear distances from the posterior superior iliac spine to each of these branches were 45.7 ± 9.3 mm (13.0–82.0 mm), 50.9 ± 9.2 mm (28.4–90.0 mm), and 56.5 ± 9.8 mm (33.1–94.0 mm), respectively (Table 1). There were no significant differences in these values between branches running through the tunnel and branches perforating the thoracolumbar fascia over the iliac crest (Table 2). The mean lengths of the osteofibrous tunnel of the medial, intermediate, and lateral branches were 6.8 ± 4.1 mm (2.0–19.0 mm), 5.8 ± 4.1 mm (1.0–16.2 mm), and 6.4 ± 5.2 mm (1.2–18.0 mm), respectively (Table 3). The length of each branch did not differ significantly among the 3 branches.

TABLE 1: Running patterns of the 3 branches of the SCN in 109 cadaveric specimens

linear distance in mm from midline to each branch over the iliac crest (Fig. 1, distance a) ± SD range linear distance in mm from posterior superior iliac spine to each branch over the iliac crest (Fig. 1, distance b) ± SD range no. of branches running through an osteofibrous tunnel


Medial Branch

Intermediate Branch

Lateral Branch

71.0 ± 7.9

76.7 ± 7.6

82.6 ± 8.2

50.0–87.5 45.7 ± 9.3

52.6–93.3 50.9 ± 9.2

55.2–106.0 56.5 ± 9.8

13.0–82.0 42 (39%)

28.4–90.0 30 (28%)

33.1–94.0 14 (13%)

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Fig. 2. Schematic illustrations of variations in the running pattern of the branches of the SCN around the iliac crest (n = 109). Numbers of specimens with each course are indicated. The dotted lines indicate the branch of the SCN under the thoracolumbar fascia. The osteofibrous tunnel is located in the black semicylindrical areas. The branches exiting from the thoracolumbar fascia into subcutaneous tissue are indicated as solid lines.

Among the branches, only 2 medial branches showed obvious entrapment in an osteofibrous tunnel. One such specimen was obtained in an 82-year-old male cadaver, and the other was in a 72-year-old female. The branches were constricted between the rigid fibers of the thoracolumbar fascia and the iliac crest. In both cases, proximal dissection of these osteofibrous tunnels revealed a bony groove on the iliac crest along the course of the medial branch (Fig. 3). In the remaining 40 specimens with branches of the medial SCN running through an osteofibrous tunnel, fatty tissue was observed around the nerve with no groove on the iliac crest (Fig. 4).

Discussion

Several researchers have reported that the medial branch of the SCN passed 70–80 mm laterally over the iliac crest,7,8,10,15 whereas other studies reported it to be 40–50 mm lateral16,21,23 to the posterior superior iliac spine. In agreement with the latter studies, the mean linear distance from the posterior superior iliac spine to the medial branch in our study was 45 mm. Including our findings, 3 of the 4 studies reporting 40–50 mm of distance used Japanese cadavers, suggesting the smaller distance was due to the smaller body size.

TABLE 2: Location of SCN branches on the iliac crest relative to the perforation point through the thoracolumbar fascia* Distance & Branch linear distance (mm) from midline to each branch over the iliac crest; Fig. 1, distance a medial ± SD intermediate ± SD lateral ± SD linear distance (mm) from posterior superior iliac spine to each branch over the iliac crest; Fig. 1, distance b medial ± SD intermediate ± SD lateral ± SD

Osteofibrous Tunnel (+)

Osteofibrous Tunnel (-)

72.2 ± 7.6 77.7 ± 6.5 80.0 ± 7.3

70.4 ± 8.0 76.2 ± 8.0 83.0 ± 8.3

45.5 ± 8.8 50.2 ± 8.2 52.9 ± 9.4

45.8 ± 9.6 51.2 ± 9.6 57.0 ± 9.8

* Osteofibrous tunnel (+) indicates branches passing through the thoracolumbar fascia below the iliac crest; osteofibrous tunnel (-) indicates the branches passing through the thoracolumbar fascia above the iliac crest. None of the comparisons were statistically significant.

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Superior cluneal nerve entrapment TABLE 3: Length of the osteofibrous tunnel and macroscopic entrapment Medial Branch

Intermediate Branch

Lateral Branch

42 6.8 ± 4.1 2.0–19.0 2 of 42 (5)

30 5.8 ± 4.1 1.0–16.2 0 of 30 (0)

14 6.4 ± 5.2 1.2–18.0 0 of 14 (0)

no. of branches length in mm of the osteofibrous tunnel ± SD range frequency of entrapment in an osteofibrous tunnel (%)

Previous anatomical studies observed that all branches of the SCN pierced the thoracolumbar fascia above the iliac crest.1,4,5,7,8,10,15,20 In contrast, Maigne and colleagues,13,14 Lu et al.,11 and Xu et al.22 all mentioned that all medial branches of the SCN passed through an osteofibrous tunnel, whereas Yazaki et al.23 reported that 95% and Moro et

al.16 that 80% of the medial branches had an osteofibrous tunnel passage. In our study, 39% of the medial branches of the SCN passed through an osteofibrous tunnel, with 28% of the intermediate branches and 13% of the lateral branches also passing through an osteofibrous tunnel. We first examined intermediate and lateral branches in terms

Fig. 3. Photographs and corresponding illustrations showing entrapment of the right medial branch of the SCN in cadaveric specimens obtained in a 72-year-old woman. Upper: The medial branch crosses over the iliac crest (curved line) through the osteofibrous tunnel (gray semicylindrical area) and is constricted within the tunnel under macroscopic observation. The branches exiting from the thoracolumbar fascia into subcutaneous tissue are indicated as a thick black line. Lower: After opening the osteofibrous tunnel (gray semicylindrical area) and retracting the medial branch (thick black line), a bony groove on the iliac crest is seen (dotted line, indicated by arrow). Postentrapment swelling is shown (arrowheads).

Fig. 4. Photographs and corresponding illustrations showing the medial and intermediate branch of the SCN on the right side with no osteofibrous tunnel entrapment in cadaveric specimens obtained in an 86-year-old woman. Upper: The medial branch of the SCN crosses over the iliac crest (curved line) through the osteofibrous tunnel (gray semicylindrical area) on the right side, but is not constricted within the tunnel. The branches exiting from the thoracolumbar fascia into subcutaneous tissue are indicated as solid lines. The intermediate branch of the SCN pierces the thoracolumbar fascia superior to the iliac crest. Lower: After opening the osteofibrous tunnel (gray semicylindrical area), abundant fatty tissue (gray circles) is seen around the medial branch.


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H. Kuniya et al. of osteofibrous tunnel and found that several variations were observed in the course of the branches. Maigne et al.13 described that 2 of 37 medial branches were compressed within an osteofibrous tunnel, and Lu et al.11 reported similar findings for 2 of 15 medial branches. We found SCN entrapment in only 2 specimens (2%), both medial branches. We did not find entrapment of the SCN in an osteofibrous tunnel to be as frequent as previously reported. Lu et al.11 reported that the average age of their cadavers was 65 years old. In our study, the cadavers had an average age of 84.8 years old. It has been suggested that the SCN entrapment in the osteofibrous tunnel might occur less frequently considering the possible increase of stenosis in the tunnel with aging. Lu et al.11 and Maigne et al.13 reported that the constricted part of the medial branch was found where the nerve passed through a rigid osteofibrous tunnel. Similarly, we noted that postentrapment nerve swelling was observed in 2 specimens. The occurrence of nerve swelling is a quite common nonspecific reaction of a nerve to various exogenous stimuli. Long-lasting direct compression of a nerve by encasement within an osteofibrous tunnel caused nerve swelling from disturbed vascularization with vasocongestion.17

Conclusions

There were several anatomical variations in the courses of the branches of the SCN. Of 109 medial branches, 42 passed through an osteofibrous tunnel. Of these 42 branches running through an osteofibrous tunnel, only 2 (5%) exhibited obvious entrapment in the tunnel. This is only 2% of the total medial branches dissected (n = 109). Entrapment in an osteofibrous tunnel was not seen as often in our study as in previous anatomical reports. Disclosure No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. Author contributions to the study and manuscript preparation include the following. Acquisition of data: Kamiya, Funakoshi, Terayama, Itoh. Drafting the article: Kuniya. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Kuniya. References 1. Aizawa Y, Kumaki K: [The courses and the segmental origins of the cutaneous branches of the thoracic dorsal rami.] Kaibogaku Zasshi 71:195–210, 1996 (Jpn) 2. Akbas M, Yegin A, Karsli B: Superior cluneal nerve entrapment eight years after decubitus surgery. Pain Pract 5:364– 366, 2005 3. Aly TA, Tanaka Y, Aizawa T, Ozawa H, Kokubun S: Medial superior cluneal nerve entrapment neuropathy in teenagers: a report of two cases. Tohoku J Exp Med 197:229–231, 2002 4. Asano S, Kaneda K: [Cause and management of donor site pain after harvesting autologous iliac bone grafts.] Sekitsui Sekizui 6:191–195, 1993 (Jpn) 5. Banwart JC, Asher MA, Hassanein RS: Iliac crest bone graft harvest donor site morbidity. A statistical evaluation. Spine (Phila Pa 1976) 20:1055–1060, 1995 6. Berthelot JM, Delecrin J, Maugars Y, Caillon F, Prost A: A

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