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The Surgical Anatomy of the Lumbosacroiliac Triangle: A Cadaveric Study
Original Article
The Surgical Anatomy of the Lumbosacroiliac Triangle: A Cadaveric Study Carmine Zoccali1,2, Jesse Skoch2, Apar S. Patel2, Christina M. Walter2, Mauricio J. Avila2, Nikolay L. Martirosyan2, Silvio Demitri3, Ali A. Baaj2
OBJECTIVE: The anatomic area delineated medially by the lateral part of the L4-L5 vertebral bodies, distally by the anterior-superior surface of the sacral wing, and laterally by an imaginary line joining the base of the L4 transverse process to the proximal part of the sacroiliac joint, is of particular interest to spine surgeons. We are referring to this area as the lumbo-sacro-iliac triangle (LSIT). Knowledge of LSIT anatomy is necessary during approaches for L5 vertebral and sacral fractures, sacral and iliac tumors, and extraforaminal decompression of the L5 nerve roots.
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METHODS: We performed an anatomic dissection of the LSIT in 3 embalmed cadavers (6 triangles), using an anterior and posterior approach.
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RESULTS: We identified 3 key tissue planes: the neurological plexus plane, constituted by L4 and L5 nerve roots; an intermediate level constituted by the ileosacral tunnel; and posteriorly, by the lumbosacral ligament, and the posterior muscular plane.
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CONCLUSIONS: Improving anatomic knowledge of the LSIT may help surgeons decrease the risk of possible complications. When LSIT pathology is present, a lateral approach corresponding to the tip of the L4 transverse process, medially, is suggested to decrease the risk of vessel and nerve root damage.
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Key words - Ascending lumbar vein - Extraforaminal compression - Ileo-lumbar ligament - Ileo-sacral ligament - Ileo-sacral tunnel - Vertebral body osteophyte Abbreviations and Acronyms ILL: Ileolumbar ligament LSIT: Lumbosacroiliac triangle LSL: Lumbosacral ligament LST: Lumbosacral tunnel
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INTRODUCTION
T
he anatomy of the lumbo-sacral region has been of great interest in recent years.1-5 The multiple vascular, nervous, and tendinous structures present in this area represent a challenge for the spine surgeon. Despite the study of this area, little has been published about the lumbosacroiliac triangle (LSIT). We define this triangle as the anatomic area delineated medially by the lateral part of the L4L5 vertebral bodies, distally by the anterior-superior surface of the sacral wing, and laterally by an imaginary line joining the base of the L4 transverse process to the proximal part of the sacroiliac joint. This area is of particular surgical interest (Figure 1). This area is often involved in spinal-pelvic trauma, degenerative disease with extraforaminal L5 root compression, and musculoskeletal tumors originating from the sacrum, iliac bone, or sacroiliac joint.6 Although the anatomy of the sacroiliac joint and the lumbosacral region are well described in the literature, no sufficient description is present regarding the area immediately proximal. With the advancement of new minimally invasive techniques, as well as more advanced complex surgical techniques, it is of utmost importance that the spine surgeon recognize fundamental structures before surgery to help decrease iatrogenic risk to neurovascular bundles of the LSIT, in particular the L5 roots. The aim of this study is to identify and clarify the surgical anatomy of the LSIT in healthy, embalmed cadavers and to encourage thorough knowledge of the anatomic structures present.
From the 1Department of Oncological Orthopaedics, Muscular-skeletal Tissue Bank, Istituti Fisioterapici Ospitalieri - Regina Elena National Cancer Institute, Rome, Italy; 2Division of Neurosurgery, University of Arizona College of Medicine, Tucson, Arizona, USA; and 3Struttura Operativa Complessa Ortopedia e Traumatologia, Azienda Ospedaliera Universitaria Udine Santa Maria della Misericordia, Udine, Italy To whom correspondence should be addressed: Carmine Zoccali, M.D., Ph.D. [E-mail: [email protected]] Citation: World Neurosurg. (2016) 88:36-40. http://dx.doi.org/10.1016/j.wneu.2015.11.083 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2016 Elsevier Inc. All rights reserved.
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ORIGINAL ARTICLE CARMINE ZOCCALI ET AL.
THE LUMBOSACROILIAC TRIANGLE ANATOMY
The right ascending lumbar artery was identified at 60, 24, and 55 mm from the aortic bifurcation. The left ascending lumbar artery was only identified in 1 cadaver, 60 mm from the aortic bifurcation. The ascending lumbar veins were bilaterally identified in each cadaver 35, 29, and 20 mm from the vena cava bifurcation on the right side, and 55, 52, and 52 mm on the left side.
Figure 1. The lumbosacroiliac triangle (transparent gray) is delineated medially by the lateral part of the L4-L5 vertebral bodies, distally by the anterior-superior surface of the sacral wing, and laterally by an imaginary line joining the base of the L4 transverse process to the proximal part of the sacroiliac joint. Proceeding from an anterior point of view, the aorta, the vena cava, and the ascending lumbar vein are visible; followed by the nervous plane (yellow), the ileosacral tunnel (marked black), and the more posterior plane of the ileolumbar ligament (green).
The Nervous Plexus The nervous plexus is the most superficial plane of interest where the L4 and L5 nerve roots and the obturator nerve can be seen (Figure 2). The L4 nerve root divides into 2 components exiting the respective foramen with a variable angle of 15e30 . The major component forms an anastomosis with the L3 root to become the femoral nerve. Further down, the minor component passes anterior to the L5 transverse process at a median distance of 8.5 mm (5 mm anterior to the L5 vertebral body, traveling laterally to the L5 root [range, 0e13 mm]) in the lateral portion of the LSIT, where the obturator nerve can also be observed. The nervous plexus plane originates from the second, third, and fourth lumbar roots, passing through the psoas major fibers (removed in Figure 2), anterior to the L4 and L5 nerve roots, traveling anteriorly and laterally along the lateral wall of the lesser pelvis. The Lumbosacral Tunnel The LST is a structure delineated laterally by the LSL and medially by the lateral aspect of the L5 vertebral body and the L5-S1 disk (Figure 3). The floor of the tunnel is represented by the anterior-
METHODS LSIT dissections were performed in 3 embalmed cadavers (6 LSITs). No sacralization or spondylolisthesis of the L5 vertebra were present in any of the cadavers. In supine position, a xyphopubic skin incision was performed. Bilateral subcostal and pubic transverse incisions were made to increase exposure. We performed dislocation and resection of the intestine and colon from the duodenum to the rectum to better visualize the retroperitoneal area. After removing the superior hypogastric plexus, the subrenal vessels were identified and dissected 4 cm distal to the bifurcation of the aorta, into internal and external iliac vessels. The psoas muscles and the L3 roots were removed for a better exposure of the lumbosacral plexus and LSIT, and dissection of the extraforaminal L5 root was performed, emphasizing the relationship with the lumbosacral ligament (LSL) and the lumbosacral tunnel (LST). The possible causes of extraforaminal compression were analyzed. The cadavers were then placed in the prone position and a second incision was made, starting at the midline, at the same height of the top of the iliac crest. The thoracolumbar fascia was cut and the erectors spinae removed. We then exposed the LSIT to describe it from a posterior view. RESULTS The aortic bifurcation was identified at L5 in 2 cadavers and in 1 at L4. The vena cava bifurcation was observed at the L4 and L5 body levels, and once at the L5-S1 disk level.
WORLD NEUROSURGERY 88: 36-40, APRIL 2016
Figure 2. The nervous plexus. The labels show L3, L4, and L5 nerve roots, the obturator nerve (obt.n.), and the ascending lumbar artery (ala). The L5 transverse process clearly divides the lumbosacroiliac triangle into superior and inferior parts.
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Figure 3. An anterior view of the lumbosacral tunnel (lst, highlighted by yellow). Tthe lumbosacral ligament (lsl) identifies the lateral wall. The L5 body and L5-S1 disk constitute the medial wall (highlighted by red and green, respectively). The anterior-superior aspect of the iliac wing represents the floor as the L5 transverse process. On the left, it is still possible to distinguish the distal segment of the L4 root. The L5 root is notable posteriorly to the ascending lumbar vein (alv). On the right, the lsl is particularly evident. The vascular bundles were removed and the position occupied by the L5 root is clearly identifiable.
superior surface of the sacral wing and the roof is only present proximally, constituted by the inferior surface of the L5 transverse process (it is a direct continuation of the L5 foramen). The LST was present in 2 cadavers; in the third, the ileosacral ligaments were vestigial. The LSL originates from the inferior portion of the L5 transverse process, about 1 cm laterally from its base, projecting inferiorly and laterally, with a variable angle of 15e40 , and inserts into the anterior-superior surface of the sacral wing, with an average length of 32.5 mm (range, 21e42 mm). In the first cadaver, the right LST entrance was 12 mm by 12 mm; the left was 12 mm by 6 mm due to the presence of an L5 body osteophyte pushing down on the nerve root at the lateral inferior edge. Distally, where the LSL ends, it is 30 mm wide, bilaterally. In the second cadaver, the dimensions of the right LST entrance were 10 mm by 12 mm; the left, 8 mm by 10 mm; the distal width was 25 mm on the right; and 18 mm on the left. The varied widths of the LST were the result of different LSL angles. In the medial aspect of the LST, we found the ascending lumbar vein. The Ileolumbar Ligament In a more posterior plane, we found the ileolumbar ligament (ILL) (Figures 4 and 5). It was present in all 6 dissected triangles. We recognized 2 components: an anterior-inferior component and a posterolateral component. The first component originated from
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the anterior tip of the L5 transverse process and projected anteriorly, inferiorly, and laterally, broadly inserting into the anteriorsuperior aspect of the iliac crest. The posterolateral component
Figure 4. The ileolumbar ligament. The anterior component is clearly evident in the main picture, from an anterior point of view. Within the inset, the posterior component is evident by a posterior access (little square).
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ORIGINAL ARTICLE CARMINE ZOCCALI ET AL.
Figure 5. The lumbosacral tunnel and the L5 root entrapped by a L5 body osteophyte (white arrow).
originated from the posterior-inferior portion of the L5 transverse process, traveling laterally and posteriorly to insert on the superomedial surface of the posterior edge of the iliac wing. Both components continued superiorly, with the anterior and posterior fascia of the quadratus lumborum muscle, respectively. In 2 of 3 cadavers, 2 components were clearly distinct (type A, Fujiwara et al7); in the third, they were fused (type B, Fujiwara et al7) and partially calcified. The anterior component had an average angle of 32 (range, 25e35 ) and length of 43 mm (range, 30e51 mm). Including insertions, the posterior component had an average angle of 20e45 and length of 31 mm (range, 25e36 mm). Just posterior to the layer represented by the ILL, we identified the spinal muscular plane, the first plane dissected during a posterior surgical approach. DISCUSSION The LSIT is a complex structure, including nerves, tendons, muscles, and vascular bundles. Anatomic knowledge of this region is important for cases involving sacral and iliac joint tumors (Figure 6A), degenerative problems with extraforaminal nerve compression6 (Figure 6B), and L5 vertebral or sacral fractures (Figure 6C). The LSIT can be involved in tumors, degeneration, and spinal or pelvic fractures with instability, usually sacrum and sacroiliac fractures.8,9 Starks et al9 found that transverse process fractures were present in 40% of patients, in a series of patients with unstable pelvic fractures. These fractures result from falls from significant heights and are often associated with L5 root
WORLD NEUROSURGERY 88: 36-40, APRIL 2016
THE LUMBOSACROILIAC TRIANGLE ANATOMY
Figure 6. (A) A pelvic computerized tomography scan of a patient affected by low-grade chondrosarcoma of the right iliac wing. In this patient, it is particularly evident that knowing lumbosacroiliac triangle (LSIT) anatomy is helpful to perform an osteotomy of the medial side of the sacrum-iliac joint. During this procedure, the L5 root is at risk of being cut. An osteotomy of the L5 transverse process may be helpful to perform a safer surgery. (B) A degenerative case where an osteophyte (arrow) is evident in the inferior part of the L5 body, protruding in the LSIT. (C) A bilateral sacral fracture (arrows) where exploration of the LSIT is important for decompression.
damage, and L5 transverse process fractures caused by dislocation of the lumbar spine and the pelvis. During the posterior approach, after detaching the tranversospinalis and erector spinae muscles, a transverse plane exists. It is constituted by the L4 and L5 transverse processes, the posteriorsuperior edge of the sacral wing, and the lateral intertransverse muscles joining them. In this plane, the LSIT is divided in 2 by the L5 transverse process and the ILL. It is unlikely the ILL is a true ligament. It is not present at birth and develops from a metaplasia at the insertion of the quadratus lumborum muscle, likely induced by upright posture, reaching maturity during the second decade of life.10 The ILL is extremely variable. Transfeldt et al11. revealed the presence of a vestigial ligament in 20% of the population, whereas, other investigators, such as Fujiwara et al,7 identified it in all 51 of their dissected specimens. It varies in size, thickness, shape, site of origin, and insertion, as well as by age, sex, and race.12 Nevertheless, it may have an important biomechanical role in stabilizing the sacroiliac joint and the lumbosacral segment.13,14 Wiltse et al,15 in 1984 were the first to recognize its pathogenic role in extraforaminal compression of the L5 root They described 2 types of
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ORIGINAL ARTICLE CARMINE ZOCCALI ET AL.
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compression. In type I the presence of a degenerative scoliosis causes the L5 transverse process to project inferiorly, narrowing the LSIT; the presence of a bulging disk, and osteophytes can further contribute to compression. Type II is more common in younger populations affected by isthmic spondylolisthesis. Slipping of the vertebra causes the transverse process to move anteriorly and inferiorly, and can cause compression with a guillotine-like effect on the L5 nerve root. Nevertheless, a strong ILL could decrease the risk of anterior slipping in spondylolysis.16 Matsumotu et al,17 in 2002, described an extraforaminal compression of L5 by osteophytes. In our dissection, 1 cadaver exhibited an osteophyte of the inferior-lateral part of the L5 body, entrapping the left L5 root; unfortunately, it was not possible to know whether the patient was symptomatic (Figure 5). Extraforaminal compression is important to consider for patients with L5 radiculopathy to decrease the likelihood of failed back surgery. Diagnosis is difficult. Computerized tomography scan and (3-dimensional) magnetic resonance imaging are helpful (Figure 6B). Nevertheless, suspicion has to be confirmed by electrophysiologic examination to reduce false-positive results.18 After dissecting the intertransverse muscles, we gained access to the anterior nervous plane. We suggest starting the dissection from the lateral part of the LSIT to reduce the risk of bleeding associated with the ascending iliac vessels, or injury to the L4 and L5 nerve roots, which are usually in the medial part of the triangle.1 Compared with other roots, L5 significantly medializes as it exits the foramen, approaching the lateral aspect of the L5 body
REFERENCES 1. Alkadhim M, Zoccali C, Abbasifard S, Avila MJ, Patel AS, Sattarov L, et al. The surgical vascular anatomy of the minimally invasive lateral lumbar interbody approach: a cadaveric and radiographic analysis. Eur Spine J. 2015;24:906-911.
and L5-S1 disk inside the LST. Careful attention must be paid for the potential presence of the L4 root, which can pass very close to the L5 root in its sagittal trajectory. Identifying the L5 root is also important during sacral or sacrum-iliac joint resection for tumor (Figure 6A). Due to its low mobility, it is in contact with bone surface, and may be involved in resection, especially when done with a Gigli saw.5 Our group showed that particular attention must be paid during LSIT dissection and total sacrectomy, where a complete sacral bilateral wing osteotomy is performed.5 A thorough LSIT dissection is essential to reduce risk of injuring the neurovascular bundles. An osteotomy of the L5 transverse process may be helpful to expand the field of view and perform a safer sacrum-iliac joint resection. Figure 6A shows a low grade chondrosarcoma of the sacro-iliac joint. Resection has to be performed in the lateral part of the sacral wing to obtain an ideal, wider margin. Access to the LSIT was particularly narrow, but osteotoming the L5 transverse process allowed us to visualize the L5 root and perform a safer osteotomy. CONCLUSION Accurate anatomic knowledge of the LSIT is imperative to safely and effectively manage conditions that affect this area. In cases where surgical LSIT pathology is present, it is important to understand the layout of the regional neurovascular anatomy before surgical intervention is undertaken.
7. Fujiwara A, Tamai K, Yoshida H, Kurihashi A, Saotome K, An HS, et al. Anatomy of the iliolumbar ligament. Clin Orthop Relat Res. 2000;380: 167-172. 8. Denis F. The three column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine (Phila Pa 1976). 1983;8: 817-831.
lumbosacral junction. Spine (Phila Pa 1976). 1990; 15:1138-1141. 15. Wiltse LL, Guyer RD, Spencer CW, Glenn WV, Porter IS. Alar transverse process impingement of the L5 spinal nerve: the far-out syndrome. Spine (Phila Pa 1976). 1984;9:31-41. 16. Aihara T, Takahashi K, Yamagata M, Moriya H, Shimada Y. Does the iliolumbar ligament prevent anterior displacement of the fifth lumbar vertebra with defects of the pars? J Bone Joint Surg Br. 2000;82:846-850.
2. Avila MJ, Skoch J, Fennell VS, Palejwala SK, Walter CM, Kim S, et al. Combined posterior hemiosteotomies and stabilization with lateral thoracotomy for en bloc resection of thoracic paraspinal primary bone tumors: technical note. J Neurosurg Spine. 2015;9:1-5.
9. Starks I, Frost A, Wall P, Lim J. Is a fracture of the transverse process of L5 a predictor of pelvic fracture instability? J Bone Joint Surg Br. 2011;93: 967-969.
3. Bina RW, Zoccali C, Skoch J, Baaj AA. Surgical anatomy of the minimally invasive lateral lumbar approach. J Clin Neurosci. 2015;22:456-459.
10. Luk KD, Ho HC, Leong JC. The iliolumbar ligament. A study of its anatomy, development and clinical significance. J Bone Joint Surg Br. 1986;68: 197-200.
17. Matsumoto M, Chiba K, Nojiri K, Ishikawa M, Toyama Y, Nishikawa Y. Extraforaminal entrapment of the fifth lumbar spinal nerve by osteophytes of the lumbosacral spine: anatomic study and a report of four cases. Spine (Phila Pa 1976). 2002;27:E169-173.
4. Zoccali C, Zoccali G, Bakaloudis G, Salducca N, Biagini R. A new technique to perform pelvic osteotomy using Gigli saw. J Surg Oncol. 2013;108: 136.
11. Transfeldt EE, Robertson D, Bradford DS. Ligaments of the lumbosacral spine and their role in possible extraforaminal spinal nerve entrapment and tethering. J Spinal Disord. 1993;6:507-512.
18. Iwasaki H, Yoshida M, Yamada H, Hashizume H, Minamide A, Nakagawa Y, et al. A new electrophysiological method for the diagnosis of extraforaminal stenosis at L5-S1. Asian Spine J. 2014;8:145-149.
5. Zoccali C, Skoch J, Patel A, Walter CM, Maykowski P, Baaj AA. The surgical neurovascular anatomy relating to partial and complete sacral and sacroiliac resections: a cadaveric, anatomic study. Eur Spine J. 2015;24:1109-1113.
12. Nathan H, Weizenbluth M, Halperin N. The lumbosacral ligament (LSL), with special emphasis on the “lumbosacral tunnel” and the entrapment of the 5th lumbar nerve. Int Orthop. 1982;6:197-202.
6. Palejwala SK, Sheen WA, Walter CM, Dunn JH, Baaj AA. Minimally invasive lateral transpsoas interbody fusion using a stand-alone construct for the treatment of adjacent segment disease of the lumbar spine: Review of the literature and report of three cases. Clin Neurol Neurosurg. 2014;124: 90-96.
13. Leong JC, Luk KD, Chow DH, Woo CW. The biomechanical functions of the iliolumbar ligament in maintaining stability of the lumbosacral junction. Spine (Phila Pa 1976). 1987;12:669-674.
Citation: World Neurosurg. (2016) 88:36-40. http://dx.doi.org/10.1016/j.wneu.2015.11.083
14. Yamamoto I, Panjabi MM, Oxland TR, Crisco JJ. The role of the iliolumbar ligament in the
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Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Received 21 June 2015; accepted 20 November 2015
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WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2015.11.083
The Surgical Anatomy of the Lumbosacroiliac Triangle: A Cadaveric Study Carmine Zoccali1,2, Jesse Skoch2, Apar S. Patel2, Christina M. Walter2, Mauricio J. Avila2, Nikolay L. Martirosyan2, Silvio Demitri3, Ali A. Baaj2
OBJECTIVE: The anatomic area delineated medially by the lateral part of the L4-L5 vertebral bodies, distally by the anterior-superior surface of the sacral wing, and laterally by an imaginary line joining the base of the L4 transverse process to the proximal part of the sacroiliac joint, is of particular interest to spine surgeons. We are referring to this area as the lumbo-sacro-iliac triangle (LSIT). Knowledge of LSIT anatomy is necessary during approaches for L5 vertebral and sacral fractures, sacral and iliac tumors, and extraforaminal decompression of the L5 nerve roots.
-
METHODS: We performed an anatomic dissection of the LSIT in 3 embalmed cadavers (6 triangles), using an anterior and posterior approach.
-
RESULTS: We identified 3 key tissue planes: the neurological plexus plane, constituted by L4 and L5 nerve roots; an intermediate level constituted by the ileosacral tunnel; and posteriorly, by the lumbosacral ligament, and the posterior muscular plane.
-
CONCLUSIONS: Improving anatomic knowledge of the LSIT may help surgeons decrease the risk of possible complications. When LSIT pathology is present, a lateral approach corresponding to the tip of the L4 transverse process, medially, is suggested to decrease the risk of vessel and nerve root damage.
-
Key words - Ascending lumbar vein - Extraforaminal compression - Ileo-lumbar ligament - Ileo-sacral ligament - Ileo-sacral tunnel - Vertebral body osteophyte Abbreviations and Acronyms ILL: Ileolumbar ligament LSIT: Lumbosacroiliac triangle LSL: Lumbosacral ligament LST: Lumbosacral tunnel
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INTRODUCTION
T
he anatomy of the lumbo-sacral region has been of great interest in recent years.1-5 The multiple vascular, nervous, and tendinous structures present in this area represent a challenge for the spine surgeon. Despite the study of this area, little has been published about the lumbosacroiliac triangle (LSIT). We define this triangle as the anatomic area delineated medially by the lateral part of the L4L5 vertebral bodies, distally by the anterior-superior surface of the sacral wing, and laterally by an imaginary line joining the base of the L4 transverse process to the proximal part of the sacroiliac joint. This area is of particular surgical interest (Figure 1). This area is often involved in spinal-pelvic trauma, degenerative disease with extraforaminal L5 root compression, and musculoskeletal tumors originating from the sacrum, iliac bone, or sacroiliac joint.6 Although the anatomy of the sacroiliac joint and the lumbosacral region are well described in the literature, no sufficient description is present regarding the area immediately proximal. With the advancement of new minimally invasive techniques, as well as more advanced complex surgical techniques, it is of utmost importance that the spine surgeon recognize fundamental structures before surgery to help decrease iatrogenic risk to neurovascular bundles of the LSIT, in particular the L5 roots. The aim of this study is to identify and clarify the surgical anatomy of the LSIT in healthy, embalmed cadavers and to encourage thorough knowledge of the anatomic structures present.
From the 1Department of Oncological Orthopaedics, Muscular-skeletal Tissue Bank, Istituti Fisioterapici Ospitalieri - Regina Elena National Cancer Institute, Rome, Italy; 2Division of Neurosurgery, University of Arizona College of Medicine, Tucson, Arizona, USA; and 3Struttura Operativa Complessa Ortopedia e Traumatologia, Azienda Ospedaliera Universitaria Udine Santa Maria della Misericordia, Udine, Italy To whom correspondence should be addressed: Carmine Zoccali, M.D., Ph.D. [E-mail: [email protected]] Citation: World Neurosurg. (2016) 88:36-40. http://dx.doi.org/10.1016/j.wneu.2015.11.083 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2016 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2015.11.083
ORIGINAL ARTICLE CARMINE ZOCCALI ET AL.
THE LUMBOSACROILIAC TRIANGLE ANATOMY
The right ascending lumbar artery was identified at 60, 24, and 55 mm from the aortic bifurcation. The left ascending lumbar artery was only identified in 1 cadaver, 60 mm from the aortic bifurcation. The ascending lumbar veins were bilaterally identified in each cadaver 35, 29, and 20 mm from the vena cava bifurcation on the right side, and 55, 52, and 52 mm on the left side.
Figure 1. The lumbosacroiliac triangle (transparent gray) is delineated medially by the lateral part of the L4-L5 vertebral bodies, distally by the anterior-superior surface of the sacral wing, and laterally by an imaginary line joining the base of the L4 transverse process to the proximal part of the sacroiliac joint. Proceeding from an anterior point of view, the aorta, the vena cava, and the ascending lumbar vein are visible; followed by the nervous plane (yellow), the ileosacral tunnel (marked black), and the more posterior plane of the ileolumbar ligament (green).
The Nervous Plexus The nervous plexus is the most superficial plane of interest where the L4 and L5 nerve roots and the obturator nerve can be seen (Figure 2). The L4 nerve root divides into 2 components exiting the respective foramen with a variable angle of 15e30 . The major component forms an anastomosis with the L3 root to become the femoral nerve. Further down, the minor component passes anterior to the L5 transverse process at a median distance of 8.5 mm (5 mm anterior to the L5 vertebral body, traveling laterally to the L5 root [range, 0e13 mm]) in the lateral portion of the LSIT, where the obturator nerve can also be observed. The nervous plexus plane originates from the second, third, and fourth lumbar roots, passing through the psoas major fibers (removed in Figure 2), anterior to the L4 and L5 nerve roots, traveling anteriorly and laterally along the lateral wall of the lesser pelvis. The Lumbosacral Tunnel The LST is a structure delineated laterally by the LSL and medially by the lateral aspect of the L5 vertebral body and the L5-S1 disk (Figure 3). The floor of the tunnel is represented by the anterior-
METHODS LSIT dissections were performed in 3 embalmed cadavers (6 LSITs). No sacralization or spondylolisthesis of the L5 vertebra were present in any of the cadavers. In supine position, a xyphopubic skin incision was performed. Bilateral subcostal and pubic transverse incisions were made to increase exposure. We performed dislocation and resection of the intestine and colon from the duodenum to the rectum to better visualize the retroperitoneal area. After removing the superior hypogastric plexus, the subrenal vessels were identified and dissected 4 cm distal to the bifurcation of the aorta, into internal and external iliac vessels. The psoas muscles and the L3 roots were removed for a better exposure of the lumbosacral plexus and LSIT, and dissection of the extraforaminal L5 root was performed, emphasizing the relationship with the lumbosacral ligament (LSL) and the lumbosacral tunnel (LST). The possible causes of extraforaminal compression were analyzed. The cadavers were then placed in the prone position and a second incision was made, starting at the midline, at the same height of the top of the iliac crest. The thoracolumbar fascia was cut and the erectors spinae removed. We then exposed the LSIT to describe it from a posterior view. RESULTS The aortic bifurcation was identified at L5 in 2 cadavers and in 1 at L4. The vena cava bifurcation was observed at the L4 and L5 body levels, and once at the L5-S1 disk level.
WORLD NEUROSURGERY 88: 36-40, APRIL 2016
Figure 2. The nervous plexus. The labels show L3, L4, and L5 nerve roots, the obturator nerve (obt.n.), and the ascending lumbar artery (ala). The L5 transverse process clearly divides the lumbosacroiliac triangle into superior and inferior parts.
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THE LUMBOSACROILIAC TRIANGLE ANATOMY
Figure 3. An anterior view of the lumbosacral tunnel (lst, highlighted by yellow). Tthe lumbosacral ligament (lsl) identifies the lateral wall. The L5 body and L5-S1 disk constitute the medial wall (highlighted by red and green, respectively). The anterior-superior aspect of the iliac wing represents the floor as the L5 transverse process. On the left, it is still possible to distinguish the distal segment of the L4 root. The L5 root is notable posteriorly to the ascending lumbar vein (alv). On the right, the lsl is particularly evident. The vascular bundles were removed and the position occupied by the L5 root is clearly identifiable.
superior surface of the sacral wing and the roof is only present proximally, constituted by the inferior surface of the L5 transverse process (it is a direct continuation of the L5 foramen). The LST was present in 2 cadavers; in the third, the ileosacral ligaments were vestigial. The LSL originates from the inferior portion of the L5 transverse process, about 1 cm laterally from its base, projecting inferiorly and laterally, with a variable angle of 15e40 , and inserts into the anterior-superior surface of the sacral wing, with an average length of 32.5 mm (range, 21e42 mm). In the first cadaver, the right LST entrance was 12 mm by 12 mm; the left was 12 mm by 6 mm due to the presence of an L5 body osteophyte pushing down on the nerve root at the lateral inferior edge. Distally, where the LSL ends, it is 30 mm wide, bilaterally. In the second cadaver, the dimensions of the right LST entrance were 10 mm by 12 mm; the left, 8 mm by 10 mm; the distal width was 25 mm on the right; and 18 mm on the left. The varied widths of the LST were the result of different LSL angles. In the medial aspect of the LST, we found the ascending lumbar vein. The Ileolumbar Ligament In a more posterior plane, we found the ileolumbar ligament (ILL) (Figures 4 and 5). It was present in all 6 dissected triangles. We recognized 2 components: an anterior-inferior component and a posterolateral component. The first component originated from
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the anterior tip of the L5 transverse process and projected anteriorly, inferiorly, and laterally, broadly inserting into the anteriorsuperior aspect of the iliac crest. The posterolateral component
Figure 4. The ileolumbar ligament. The anterior component is clearly evident in the main picture, from an anterior point of view. Within the inset, the posterior component is evident by a posterior access (little square).
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2015.11.083
ORIGINAL ARTICLE CARMINE ZOCCALI ET AL.
Figure 5. The lumbosacral tunnel and the L5 root entrapped by a L5 body osteophyte (white arrow).
originated from the posterior-inferior portion of the L5 transverse process, traveling laterally and posteriorly to insert on the superomedial surface of the posterior edge of the iliac wing. Both components continued superiorly, with the anterior and posterior fascia of the quadratus lumborum muscle, respectively. In 2 of 3 cadavers, 2 components were clearly distinct (type A, Fujiwara et al7); in the third, they were fused (type B, Fujiwara et al7) and partially calcified. The anterior component had an average angle of 32 (range, 25e35 ) and length of 43 mm (range, 30e51 mm). Including insertions, the posterior component had an average angle of 20e45 and length of 31 mm (range, 25e36 mm). Just posterior to the layer represented by the ILL, we identified the spinal muscular plane, the first plane dissected during a posterior surgical approach. DISCUSSION The LSIT is a complex structure, including nerves, tendons, muscles, and vascular bundles. Anatomic knowledge of this region is important for cases involving sacral and iliac joint tumors (Figure 6A), degenerative problems with extraforaminal nerve compression6 (Figure 6B), and L5 vertebral or sacral fractures (Figure 6C). The LSIT can be involved in tumors, degeneration, and spinal or pelvic fractures with instability, usually sacrum and sacroiliac fractures.8,9 Starks et al9 found that transverse process fractures were present in 40% of patients, in a series of patients with unstable pelvic fractures. These fractures result from falls from significant heights and are often associated with L5 root
WORLD NEUROSURGERY 88: 36-40, APRIL 2016
THE LUMBOSACROILIAC TRIANGLE ANATOMY
Figure 6. (A) A pelvic computerized tomography scan of a patient affected by low-grade chondrosarcoma of the right iliac wing. In this patient, it is particularly evident that knowing lumbosacroiliac triangle (LSIT) anatomy is helpful to perform an osteotomy of the medial side of the sacrum-iliac joint. During this procedure, the L5 root is at risk of being cut. An osteotomy of the L5 transverse process may be helpful to perform a safer surgery. (B) A degenerative case where an osteophyte (arrow) is evident in the inferior part of the L5 body, protruding in the LSIT. (C) A bilateral sacral fracture (arrows) where exploration of the LSIT is important for decompression.
damage, and L5 transverse process fractures caused by dislocation of the lumbar spine and the pelvis. During the posterior approach, after detaching the tranversospinalis and erector spinae muscles, a transverse plane exists. It is constituted by the L4 and L5 transverse processes, the posteriorsuperior edge of the sacral wing, and the lateral intertransverse muscles joining them. In this plane, the LSIT is divided in 2 by the L5 transverse process and the ILL. It is unlikely the ILL is a true ligament. It is not present at birth and develops from a metaplasia at the insertion of the quadratus lumborum muscle, likely induced by upright posture, reaching maturity during the second decade of life.10 The ILL is extremely variable. Transfeldt et al11. revealed the presence of a vestigial ligament in 20% of the population, whereas, other investigators, such as Fujiwara et al,7 identified it in all 51 of their dissected specimens. It varies in size, thickness, shape, site of origin, and insertion, as well as by age, sex, and race.12 Nevertheless, it may have an important biomechanical role in stabilizing the sacroiliac joint and the lumbosacral segment.13,14 Wiltse et al,15 in 1984 were the first to recognize its pathogenic role in extraforaminal compression of the L5 root They described 2 types of
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ORIGINAL ARTICLE CARMINE ZOCCALI ET AL.
THE LUMBOSACROILIAC TRIANGLE ANATOMY
compression. In type I the presence of a degenerative scoliosis causes the L5 transverse process to project inferiorly, narrowing the LSIT; the presence of a bulging disk, and osteophytes can further contribute to compression. Type II is more common in younger populations affected by isthmic spondylolisthesis. Slipping of the vertebra causes the transverse process to move anteriorly and inferiorly, and can cause compression with a guillotine-like effect on the L5 nerve root. Nevertheless, a strong ILL could decrease the risk of anterior slipping in spondylolysis.16 Matsumotu et al,17 in 2002, described an extraforaminal compression of L5 by osteophytes. In our dissection, 1 cadaver exhibited an osteophyte of the inferior-lateral part of the L5 body, entrapping the left L5 root; unfortunately, it was not possible to know whether the patient was symptomatic (Figure 5). Extraforaminal compression is important to consider for patients with L5 radiculopathy to decrease the likelihood of failed back surgery. Diagnosis is difficult. Computerized tomography scan and (3-dimensional) magnetic resonance imaging are helpful (Figure 6B). Nevertheless, suspicion has to be confirmed by electrophysiologic examination to reduce false-positive results.18 After dissecting the intertransverse muscles, we gained access to the anterior nervous plane. We suggest starting the dissection from the lateral part of the LSIT to reduce the risk of bleeding associated with the ascending iliac vessels, or injury to the L4 and L5 nerve roots, which are usually in the medial part of the triangle.1 Compared with other roots, L5 significantly medializes as it exits the foramen, approaching the lateral aspect of the L5 body
REFERENCES 1. Alkadhim M, Zoccali C, Abbasifard S, Avila MJ, Patel AS, Sattarov L, et al. The surgical vascular anatomy of the minimally invasive lateral lumbar interbody approach: a cadaveric and radiographic analysis. Eur Spine J. 2015;24:906-911.
and L5-S1 disk inside the LST. Careful attention must be paid for the potential presence of the L4 root, which can pass very close to the L5 root in its sagittal trajectory. Identifying the L5 root is also important during sacral or sacrum-iliac joint resection for tumor (Figure 6A). Due to its low mobility, it is in contact with bone surface, and may be involved in resection, especially when done with a Gigli saw.5 Our group showed that particular attention must be paid during LSIT dissection and total sacrectomy, where a complete sacral bilateral wing osteotomy is performed.5 A thorough LSIT dissection is essential to reduce risk of injuring the neurovascular bundles. An osteotomy of the L5 transverse process may be helpful to expand the field of view and perform a safer sacrum-iliac joint resection. Figure 6A shows a low grade chondrosarcoma of the sacro-iliac joint. Resection has to be performed in the lateral part of the sacral wing to obtain an ideal, wider margin. Access to the LSIT was particularly narrow, but osteotoming the L5 transverse process allowed us to visualize the L5 root and perform a safer osteotomy. CONCLUSION Accurate anatomic knowledge of the LSIT is imperative to safely and effectively manage conditions that affect this area. In cases where surgical LSIT pathology is present, it is important to understand the layout of the regional neurovascular anatomy before surgical intervention is undertaken.
7. Fujiwara A, Tamai K, Yoshida H, Kurihashi A, Saotome K, An HS, et al. Anatomy of the iliolumbar ligament. Clin Orthop Relat Res. 2000;380: 167-172. 8. Denis F. The three column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine (Phila Pa 1976). 1983;8: 817-831.
lumbosacral junction. Spine (Phila Pa 1976). 1990; 15:1138-1141. 15. Wiltse LL, Guyer RD, Spencer CW, Glenn WV, Porter IS. Alar transverse process impingement of the L5 spinal nerve: the far-out syndrome. Spine (Phila Pa 1976). 1984;9:31-41. 16. Aihara T, Takahashi K, Yamagata M, Moriya H, Shimada Y. Does the iliolumbar ligament prevent anterior displacement of the fifth lumbar vertebra with defects of the pars? J Bone Joint Surg Br. 2000;82:846-850.
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9. Starks I, Frost A, Wall P, Lim J. Is a fracture of the transverse process of L5 a predictor of pelvic fracture instability? J Bone Joint Surg Br. 2011;93: 967-969.
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4. Zoccali C, Zoccali G, Bakaloudis G, Salducca N, Biagini R. A new technique to perform pelvic osteotomy using Gigli saw. J Surg Oncol. 2013;108: 136.
11. Transfeldt EE, Robertson D, Bradford DS. Ligaments of the lumbosacral spine and their role in possible extraforaminal spinal nerve entrapment and tethering. J Spinal Disord. 1993;6:507-512.
18. Iwasaki H, Yoshida M, Yamada H, Hashizume H, Minamide A, Nakagawa Y, et al. A new electrophysiological method for the diagnosis of extraforaminal stenosis at L5-S1. Asian Spine J. 2014;8:145-149.
5. Zoccali C, Skoch J, Patel A, Walter CM, Maykowski P, Baaj AA. The surgical neurovascular anatomy relating to partial and complete sacral and sacroiliac resections: a cadaveric, anatomic study. Eur Spine J. 2015;24:1109-1113.
12. Nathan H, Weizenbluth M, Halperin N. The lumbosacral ligament (LSL), with special emphasis on the “lumbosacral tunnel” and the entrapment of the 5th lumbar nerve. Int Orthop. 1982;6:197-202.
6. Palejwala SK, Sheen WA, Walter CM, Dunn JH, Baaj AA. Minimally invasive lateral transpsoas interbody fusion using a stand-alone construct for the treatment of adjacent segment disease of the lumbar spine: Review of the literature and report of three cases. Clin Neurol Neurosurg. 2014;124: 90-96.
13. Leong JC, Luk KD, Chow DH, Woo CW. The biomechanical functions of the iliolumbar ligament in maintaining stability of the lumbosacral junction. Spine (Phila Pa 1976). 1987;12:669-674.
Citation: World Neurosurg. (2016) 88:36-40. http://dx.doi.org/10.1016/j.wneu.2015.11.083
14. Yamamoto I, Panjabi MM, Oxland TR, Crisco JJ. The role of the iliolumbar ligament in the
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Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Received 21 June 2015; accepted 20 November 2015
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WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2015.11.083