Vertebral anatomy





A detailed understanding of spinal anatomy is requisite to performing spinal procedures. The spine consists of bones, ligaments, discs, blood vessels, and nerves.


Bony structures and ligaments of the spine


The bony components of the spine, or vertebrae, begin at the transition from the skull to the cervical spine, also known as the craniocervical junction . In total, 33 bones make up the entire vertebral column. Of these bones, 24 are individually separate though linked to each other through joints and ligaments to provide both support and flexibility. The lower nine bones are fused in adults and make up the sacrum and coccyx ( Fig. 1.1 ). This chapter will focus on the upper 24 vertebrae.




Fig. 1.1


Anterior, posterior, and lateral views of bony structures of the spine.

(From Cleveland Clinic Center for Medical Art & Photography © 2011–2015. All rights reserved. With permission.)


The upper 24 vertebrae can be divided into 7 cervical, 12 thoracic, and 5 lumbar. Accurate and consistent numbering of vertebrae is critical in guiding interventions. Therefore, it is important to note anatomical variants that may be encountered, including L5 sacralization, which is incorporation of the L5 vertebral body into the sacrum ( Fig. 1.2 ).




Fig. 1.2


Sacralization. L5 fuses fully or partially into the sacrum, on one or both sides. Sacralization is a congenital anomaly.

(From Doo AR, Lee J, Yeo GE, et al. The prevalence and clinical significance of transitional vertebrae: a radiologic investigation using whole spine spiral three-dimensional computed tomographic images. Anesth Pain Med . 2020;15(1):103-110, Fig. 2.)


The vertebrae are arranged such that, when in the upright position, they make naturally occurring curves. These curves assist in the spine’s ability to distribute vertical compressive forces. When viewed from the side, the cervical and lumbar spines appear concave, known as lordosis , whereas the thoracic spine appears convex, known as kyphosis ( Fig. 1.3 ).




Fig. 1.3


Natural curvature of the spine.

(From Patton K, Thibodeau G, Douglas M. Essentials of Anatomy and Physiology. Elsevier; 2012: 161, Fig. 9.10.)


While there are structural variations, most of the vertebrae are composed of an anterior part and a posterior part. The anterior part of a vertebra contains the vertebral body. Externally, it is made of a hard shell of compact bone; internally, it consists of marrow-containing trabecular bone, which is innervated by the sinuvertebral and basivertebral nerves ( Fig. 1.4 ).




Fig. 1.4


Vertebral structure. (Left) A vertebra is split into the vertebral arch posteriorly and vertebral body anteriorly. (Right) The body is made up of trabecular bone surrounded by a cortical shell. Superiorly and inferiorly is the end-plate region, atop which sits the intervertebral disc.

(Modified from Auger JD, Frings N, Wu Y, et al. Trabecular architecture and mechanical heterogeneity effects on vertebral body strength. Curr Osteoporos Rep. 2020;18:716-726, Fig. 1.)


Each vertebral body is separated by intervertebral discs that sit between adjacent vertebrae. These discs aid in load bearing and are discussed later. The posterior part of a vertebra contains the vertebral arch, which includes the pedicle, lamina, spinous process, transverse process, and superior and inferior articular processes, which form the facet or zygapophyseal joints ( Fig. 1.5 ).




Fig. 1.5


Lumbar vertebra, superior view ( left ) and lateral view ( right ). B, Vertebral body; C, spinal canal; IAP, inferior articulating process; L, lamina; P, pedicle; PI, pars interarticularis; SAP, superior articulating process; SP, spinous process; TP, transverse process.

(Modified from Manjila SV, Mroz, TE, Steinmetz MP. Lumbar Interbody Fusions , 1st ed. Elsevier; 2018. chap 3, 19-21, Figs. 3.1 and 3.2.)


The pedicles connect the vertebral body to the transverse processes as well as the laminae, together creating the arch, which helps encase the spinal cord. Nerve roots exit inferior to each pedicle; thus, the pedicle is a key anatomical landmark to identify during needle placement for interventional procedures. With fluoroscopic imaging, pedicles appear as rounded areas of increased bone density ( Fig. 1.6 ).




Fig. 1.6


The “Scotty dog” in lumbar oblique projections that assists in identifying fluoroscopic landmarks. (A) Fluoroscopic image with needle in position for a supra-neural transforaminal epidural steroid injection. (B) How the anatomical landmarks create the “Scotty dog” outline and eye. IAP, Inferior articular process—front and back legs; IEP, inferior endplate; LAM, lamina—body; P, pedicle—eye; PI, pars interarticularis—neck; SAP, superior articular process—ear; SEP, superior endplate; SP, spinous process—tail.

(From Furman MB. Atlas of Image-Guided Spinal Procedures . 2nd ed. Elsevier; 2018:chap 3, 27-65, Fig. 3.20.)


The laminae connect the transverse processes to the spinous process and form the roof of the spinal canal through which the spinal cord travels. The spinous process is the point for muscle and ligament attachment, notably, those muscles used for extension of the vertebral column. The articular processes also project from the laminae and allow a vertebra to articulate with the vertebrae above and below it to form the zygapophyseal, or facet, joints ( Fig. 1.7 ).




Fig. 1.7


Facet joints in lateral view.

(From Mahadevan V. Anatomy of the vertebral column. Surgery (Oxford) . 2018;36(7):327-332, Fig. 4.)


The thicker portion of the lamina that acts as the junction connecting the spinous processes to the superior and inferior articular processes on a single vertebra is known as the pars interarticularis . It is prone to “pars defects,” or fractures known as spondylolysis , which can lead to the displacement of a vertebral body, known as spondylolisthesis ( Fig. 1.8 ). Spondylolisthesis can result in nerve root compression.




Fig. 1.8


Top ( left and right ) showing a defect in the pars interarticularis (PI), termed spondylolysis . Bottom showing sagittal views of the spine with the intact PI (A), pars defect (B), or spondylolysis, and anterior displacement of the L5 vertebral body (C), or spondylolisthesis.

(Modified from Chakravarthy V, Patel A, Kemp W, Steinmetz M. Surgical treatment of lumbar spondylolisthesis in the elderly. Neurosur Clin N Am . 2019;30(3):341-352.)


Cervical spine


The superior-most vertebra, C1, is termed the atlas . The second, C2, is termed the axis ( Fig. 1.9 ). Together, they account for most of the rotational ability of the cervical spine. C1 attaches the skull to the spine. It is unlike the other vertebrae in that it lacks a vertebral body and a spinous process. It is shaped like a ring: two lateral masses are connected by an anterior and posterior arch. The anterior arch comes to a midpoint that contains the dorsal facet, which allows for a connection with the dens on the vertebral body of C2, allowing C1 to pivot the skull. , The posterior arch of C1 contains the posterior tubercle at its midpoint, which serves as the origin for the rectus capitis posterior minor muscle, which assists head and neck extension. ,




Fig. 1.9


The C1 ( left ) and C2 ( right ) vertebrae.

(From Bazira PJ. Clinically applied anatomy of the vertebral column. Surgery . 2021;39(6):315-323, Fig. 4.)


In the posterior portion of each posterior arch is a groove in which the vertebral artery and first cervical spinal nerve are found. Injecting in this region can be technically challenging. The posterior cavity of the atlas formed by the anterior and posterior arches contains the spinal cord. The lateral masses of C1 contain the superior articular processes/facets that connect it to the occiput, or skull base, and inferior articular processes that connect it to C2.


The C2 vertebra, or the axis, is composed of a body that contains a vertical pillar of bone, the dens, which articulates with C1 above. The inferior facets are located at the junction of the pedicles and laminae. The spinous process of C2 is bifid and provides a prominent bony landmark for palpation. It is also the attachment for several suboccipital muscles and the ligamentum nuchae (nuchal ligament), which extends from the external occipital protuberance to the C7 spinous process.


The lower cervical vertebrae (C3–C7) adopt the more usual vertebral structure detailed previously, but they are distinguished (except for C7) by the presence of a perforation in each transverse process, termed the foramen transversarium , that transmits the vertebral artery and sympathetic plexuses ( Fig. 1.10 ). Further, the spinous processes of C3 to C6 are bifid, whereas the spinous process of C7 is monofid. The spinal canal of the cervical vertebrae is triangular; its anterior border is the vertebral body, its lateral borders are the pedicles, and its posterior border is the laminae. The transverse process in the cervical vertebrae is unique not only because it contains the foramen transversarium but also in that it gives off two tubercles, anterior and posterior, that attach the scalene muscles used for lateral neck flexion. The anterior tubercle of C6 is notable in that it is termed the carotid tubercle and is immediately posterior to the carotid artery.




Fig. 1.10


Features of typical cervical vertebrae from C3 to C6. The C7 vertebra is distinguished in that it has a monofid spinous process and no foramen transversarium.

(From Bazira PJ. Clinically applied anatomy of the vertebral column . Surgery . 2021;39(6):315-323, Fig. 3.)


Thoracic spine


The thoracic region is the least mobile area of the spine, partly due to stability provided by the rib cage and sternum. A primary function of the thoracic spine, in connection with the ribs and sternum, is protection of thoracic organs, including the heart and lungs. The bodies of the thoracic spine vertebrae are unique in that their upper and lower lateral borders house areas, known as demi-facets , for articulation with the heads of the ribs ( Fig. 1.11 ).




Fig. 1.11


Thoracic vertebra superior view ( top ) and lateral view ( bottom ). The characteristic feature of thoracic vertebrae is the presence of rib facets/demi-facets, joints that articulate with ribs.

(GD Cramer, SA Darby Basic and clinical anatomy of the spine, spinal cord, and ANS (2nd ed.), Elsevier Mosby, St Louis (2005))


The posterior arches of the thoracic vertebrae contain the same components as those seen in Fig. 1.5 : the vertebral foramen, pedicles, superior and inferior articular processes, spinous processes, and transverse processes. The spinous processes of thoracic vertebrae are more acutely slanted caudad.


There are usually 12 ribs on each side of the thoracic vertebra. Ribs 1 to 7 are true ribs in that they connect to the costal cartilage of the sternum anteriorly; ribs 8 to 12 are false ribs in that their costal cartilages are connected to the rib above. Ribs 11 and 12 are also floating ribs, which do not project anteriorly.


Lumbar spine


Five vertebrae compose the lumbar portion of the spine. The vertebral bodies are large, and the posterior arch, formed by the pedicles, laminae, and articular processes, encloses the vertebral foramen. These vertebrae are unique in their lack of costal facets and foramen transversaria ( Fig. 1.12 ). The spinous processes are near horizontal, making for large interlaminar spaces that are easily visualized using a fluoroscopic approach during interventions ( Fig. 1.13 ). ,




Fig. 1.12

Aug 6, 2023 | Posted by in ANESTHESIA | Comments Off on Vertebral anatomy

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