j o u r n a l o f t h e a n a t o m i c a l s o c i e t y o f i n d i a 6 4 ( 2 0 1 5 ) 1 6 6 – 1 7 3 Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/jasi Review Article Clinical anatomy and significance of the lumbar intervertebral foramen: A review a b,c, Grigorios Gkasdaris , Stylianos Kapetanakis * a Department of Anatomy, Medical School, Democritus University of Thrace, Alexandroupolis 68100, Greece b Orthopaedic Surgeon-Spine Surgeon, Lecturer of Anatomy, Department of Anatomy, Medical School, Democritus University of Thrace, Alexandroupolis 68100, Greece c European Interbalkan Medical Center, Thessaloniki 57001, Greece a r t i c l e i n f o a b s t r a c t Article history: The objective of this review is to summarize the knowledge about the anatomy of the lumbar Received 8 August 2015 intervertebral foramen (IVF) as an anatomic entity. The intervertebral or neural foramen is Accepted 26 October 2015 an orifice located between any two adjacent vertebrae that allows communication between Available online 23 November 2015 the spinal canal and the extraspinal region. We describe the osseous structure of the lumbar foramen, the adjacent ligaments and its components including the arteries and veins Keywords: passing through or neighboring it, and the spinal nerves and roots. Although lumbar spine structures are familiar to spinal surgeons and many procedures are performed in the area of Lumbar intervertebral foramen Anatomy the lumbar IVF, yet surprisingly little is known about the precise anatomy of the foramen Clinical and the triangular working zone of it. # 2015 Anatomical Society of India. Published by Elsevier, a division of Reed Elsevier Triangular working zone India, Pvt. Ltd. All rights reserved. Safe zone Review highly sensitive spinal cord and spinal nerve roots. At the 1. Introduction same time, it is highly flexible, providing mobility in many different planes including flexion, extension, side bending, 2,3 Generally, the lumbar spine consists of five moveable and rotation as mentioned. vertebrae numbered L1–L5. The lumbar spine is characterized The intervertebral foramen (IVF), referring to the lumbar IVF by complex anatomy, which is a remarkable combination of also, serves as the path between the spinal canal and periphery, these strong vertebrae, multiple osseous elements linked by through which canal neurovascular structures pass. This joint capsules, and flexible ligaments/tendons, large muscles, foramen is unique in comparison to other foramens of the and highly sensitive nerves. It also has a complicated body due to its boundaries consisting of two movable joints: the innervation and vascular supply as described by Drake ventral intervertebral joint and the dorsal zygapophysial joint. 1 et al. It is designed to be incredibly strong, protecting the The proximity of these joints increases susceptibility of * Corresponding author. E-mail address: [email protected] (S. Kapetanakis). Abbreviations: IVF, intervertebral foramen; CSF, cerebrospinal fluid; DRG, dorsal root ganglia; TFL, transforaminal ligament; LSTV, lumbosacral transitional vertebra; ED, endoscopic discectomy; MRN, magnetic resonance neurography; PELD, posterolateral endoscopic lumbar discectomy. http://dx.doi.org/10.1016/j.jasi.2015.10.003 0003-2778/# 2015 Anatomical Society of India. Published by Elsevier, a division of Reed Elsevier India, Pvt. Ltd. All rights reserved. j o u r n a l o f t h e a n a t o m i c a l s o c i e t y o f i n d i a 6 4 ( 2 0 1 5 ) 1 6 6 – 1 7 3 167 Table 1 – Articles where the anatomy of lumbar IVF is described as a whole. Level of evidence Study aim Date Authors Journal Level IV Ligament, nerve, and blood vessel anatomy of the lateral 2015 Yuan SG, Wen YL, Zhang P, Int Orthop zone of the lumbar intervertebral foramina Li YK Level V Radiographic anatomy of the intervertebral cervical and 2012 Demondion X, Lefebvre G, Diagn Interv lumbar foramina (vessels and variants) Fisch O Imaging Level IV Anatomy of the intervertebral foramen 2002 Gilchrist RV, Slipman CW, Pain Phys Bhagia SM Level IV Lumbar lateral recess and intervertebral foramen. Radio- 2000 Demondion X, Manelfe C, J Radiol anatomical study Prere J, Francke JP Level IV Chirurgische Anatomie und Pathologie der lumbalen 1994 Steinsiepe KF Aktuelle Probl Intervertebralforamina [Surgical anatomy and pathology Chir Orthop of lumbar intervertebral foramina] narrowing from arthritic structural alterations and lesions. 2.2. Components Specifically, the lumbar IVF has a critical role in spinal stenosis 4,5 and other degenerative spine disorders. The vertebral canal contains the spinal cord, its meninges, Although lumbar spine structures are familiar to spinal spinal nerve roots, and blood vessels supplying the cord, surgeons, yet surprisingly little is known about the precise vertebrae, joints, muscles, and ligaments. The vertebral bodies anatomy of the IVF as an anatomic entity (as seen in Table 1), and discs compose the anterior border, while the laminae and particularly the ligamentous structure associated with this ligamentum flavum create the posterior border of the canal. canal. Furthermore, only a few studies have described the Laterally, spinal nerves and vessels travel through the IVF. anatomy of this region but not in depth and not as a whole. Numerous components are together in the IVF: nerve roots Additionally, a lack of schematic depiction of the foraminal and spinal ganglions, foraminal fat, foraminal veins, radicular components and their anatomical relationships can be arterioles, lymph vessels, the meningeal nerve and foraminal observed. To elucidate the clinical significance of the lumbar ligaments (see Fig. 2). The total area of the neurovascular 11 IVF, we study this foramen as an anatomical entity including bundle is estimated at 20–50% of the total foraminal area. spinal nerve roots, vessels, and osseous and ligamentous The anterior motor root joins the posterior sensory root just structures, and we further proceed to their schematic after the spinal ganglion in order to form the mixed spinal illustration. The following review is a thorough anatomic nerve. The spinal ganglion is located below the pedicle. At the description of the IVF, with its contents, from L1 to L5 level. foramen exit, the spinal nerve usually divides into a relatively 2. The lumbar IVF 2.1. Anatomical boundaries This foramen has two parts: one anterosuperior, made up of the inferior part of the pedicle and the posteroinferior part of the vertebral body (see Fig. 1); the other is inferior and mobile; it is formed by the posterior articular lamina covered by the yellow ligament, in the back, and by the posterolateral aspect 6,7 of the intervertebral disk in front. This second articular part is the one that undergoes motion-related or degenerative changes. At the lumbar spine, the foramen has an oval shape with a large vertical axis. The L5-S1 foramen is the roundest and the smallest of the lumbar intervertebral foramina. The spinal ganglion occupies the largest part of the foramen at this 8,9 segment. In extreme flexion, all the diameters of the IVF are at their maximum; the pedicles move apart from each other, 10 disk convexity is minimal as reported by Revel et al. On the other hand, during extension, all the diameters diminish; the pedicles move closer to each other, reducing the height of the 11.12 foramen by approximately 20%. The collapse of the lumbar IVF equals to the reduction in foraminal height. Thus, as long Fig. 1 – (1) Vertebral body, (2) Intervertebral disk, (3) Pars as the height of the intervertebral space remains satisfactory, interarticularis, (4) Transverse process, (5) Intervertebral the passage of nerve components in the bony upper part of the foramen, (6) Superior vertebral notch, (7) Inferior vertebral foramen is protected in a way from disk protrusion, posterior notch, (8) Superior articular process, (9) Inferior articular facet joint osteoarthritis, and ascension of the inferior articular process, (10) Zygapophysial joint, (11) Lamina, (12) Spinous process during extension movements. process, (13) Lumbo-sacral joint, (14) Sacrum. 168 j o u r n a l o f t h e a n a t o m i c a l s o c i e t y o f i n d i a 6 4 ( 2 0 1 5 ) 1 6 6 – 1 7 3 ligaments. Each IVF is bounded superiorly and inferiorly by the pedicle, anteriorly by the intervertebral disk and vertebral body, and posteriorly by facet joints. When looking outward from the spinal canal the IVF has the appearance of an oval, teardrop-shaped window. The upper border of the IVF is the inferior aspect of the vertebral notch of the pedicle of the superior vertebra, the ligamentum flavum at its outer free edge, and posteriorly lays the pars interarticularis and the zygapophysial joint. The lower point of the nerve root canal is the superior vertebral notch of the pedicle of the inferior vertebra, postero-inferior margin of the superior vertebral body, the intervertebral disk, and the postero-superior margin of the inferior vertebral body. One of the major symptoms referred to the lumbar spine and the lumbar IVF is low back pain. Its origins have been a matter of great controversy and have been linked to spinal Fig. 2 – Disk angled axial T2 FSE at L4/5 level. (1) Disk, stenosis. While spinal stenosis is now radiologically depict- (2) Spinal canal, (3) Nerve roots, (4) Intervertebral foramen able, the alteration of the foramen borders is less clear. The with its components, (5) Exiting nerve root, (6) Facet joints, narrowing of the maximum IVF width is excluded as the only (7) Spinous process. cause of radiculopathy or spinal stenosis and in a similar way 16,17 the decrease of the IVF height is considered insignificant.