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Cervical Spine Anatomy

  • Bobby G. YowEmail author
  • Andres S. Piscoya
  • Scott C. Wagner
Living reference work entry
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Abstract

An in depth understanding of cervical spine anatomy is essential to the diagnosis and management of cervical spine pathology. From the osseous anatomy down to the soft tissues structures that function to stabilize, maintain, and protect the spinal cord clinicians must be able to appreciate the biomechanics and the complex anatomy. For patients managed operatively, appropriate surgical planning and operative technique rely heavily upon a sound understanding of the intricate anatomy in this region. In this chapter we detail the cervical spine anatomy with particular emphasis on the osseous, muscular, ligamentous, and neurovascular tissues with the goal of providing clinicians a comprehensive review that they can depend on and refer to when treating patients with cervical spine disease.

Keywords

Anatomy Cervical spine Vertebrae Review 

Introduction

The cervical spine consists of seven vertebrae. Each is named according to its corresponding order from C1 cranially to C7 caudally. After completion of embryonic development first two vertebrae are unique in that they do not contain a typical vertebral body and are referred to as the “atlas” (C1) and “axis” (C2), respectively (Fig. 1). These two vertebrae form the atlantoaxial complex of the upper cervical spine. The remaining vertebra (C3–C7) is referred to as the subaxial cervical spine. The overall sagittal plane alignment is concave posteriorly, resulting in an overall lordotic curvature to a normal cervical spine. Each vertebra has an associated nerve root exiting bilaterally above the pedicle and through the foramina, which are referred to as C1–C7. The C8 nerve root exits below the pedicle of C7.
Fig. 1

Midsagittal graphical representation of the upper cervical spine. (By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body: Gray’s Anatomy, Plate 308, Public Domain)

Atlantoaxial Complex

C1

The C1 vertebra (atlas) is a ring-shaped structure that is unique from C3 to C7 in that it lacks a robust vertebral body. It instead has an anterior tubercle, which is the attachment site for the longus colli muscle. On the posterior aspect of the ring is the posterior tubercle, which provides attachment points for the rectus capitis posterior minor muscle and the suboccipital membrane. Both the lateral aspects of the anterior and posterior tubercles create semicircular structures called the anterior and posterior arches. The junction of these arches on the lateral-most aspect of the rings form the lateral masses. Each lateral mass is composed of an articular process on both the superior and inferior aspects of the lateral mass. The superior articular process is concave and oriented inferiorly and medially, allowing for a congruent articulation with the occiput bilaterally. Inferiorly, the processes are oriented with a sloped angle inferiorly and laterally, allowing for an articulation with the superior articular processes of C2 (axis) (Daniels et al. 1983; Parke and Sherk 1989). Just posterior to the lateral mass is a subtle groove, in which the vertebral artery courses. The atlas’ superior and inferior articulations allow for primarily flexion and extension, as well as lateral bending (Panjabi et al. 1991a). On the posterior aspect of the anterior tubercle, on the inner aspect of the anterior arch at the midline, is a subtle indention that allows for an articulation with the dens of the axis (Fig. 2). Additionally, there are insertion sites just anterior and medial to the lateral masses on the inner aspect of the ring for the transverse ligaments, which also attach to the posterior aspect of the dens of the axis. Extending laterally from each lateral mass is the transverse process. The transverse process at this level houses the vertebral arteries before they exit the vertebral column and enter the foramen magnum in order to become an intracranial structure. A subset of the population has an anatomic variation consisting of an osseous bridge that covers the ridge containing the vertebral artery; this variation is termed an arcuate foramen or ponticulus posticus and is estimated to have a 3–15% prevalence in the population.
Fig. 2

Axial representation of the C1 vertebra, or atlas. (By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body: Gray’s Anatomy, Plate 86, Public Domain)

C2

Like C1, the C2 vertebra (axis) is unique in that has a bony prominence that projects cranially termed the odontoid process or dens. Anteriorly, the odontoid has a synovial articulation with the posterior aspect of the anterior tubercle of the atlas. This articulation allows for nearly half of the rotatory movement of the head and cervical spine. The posterior aspect of the odontoid has two subtle prominences that are the attachment sites of the alar ligaments, which span the atlas and attach medial to the posterior occipital condyles. These ligaments insert laterally at the base of the skull and provide stabilization of the atlantoaxial complex. The apical ligament attaches at the apex of the odontoid, which subsequently attaches to the anterior aspect of the foramen magnum at the midline. The primary stabilizer of the odontoid to the atlas is the transverse ligament, which is a structure that spans the anterior arch of the atlas and is a restraint to lateral displacement of the odontoid. The transverse ligament also has cephalad and caudal projections at the midline termed the cruciform ligaments which provide additional stability to the atlantoaxial complex. Posteriorly, the axis contains a bifid spinous process that serves as the attachment site for the rectus capitis posterior major and obliquus capitis inferior muscles attach. On the lateral aspects of the axis, there are both superior and inferior articular processes which articulate with the analogous structures on the adjacent vertebrae. The superior facet is sloped inferior laterally, congruent with the inferior facets of the lateral masses of the atlas. It is important to note that the sagittal diameter of the spinal canal in the upper cervical spine is greater than that of the lower cervical spine, allowing for adequate space for both the odontoid and the spinal cord. Steel’s rule of thirds classically states that one-third of the canal diameter is occupied by the odontoid, one-third by the spinal cord, and the remaining one-third as free space preventing compression of the cord (Ebraheim et al. 1998). The transverse processes of the axis are directed caudally, containing the foramen transversaria that houses the vertebral arteries (Fig. 3).
Fig. 3

Axial representation of the C2 vertebra, or atlas. (By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body: Gray’s Anatomy, Plate 87, Public Domain)

Subaxial Cervical Spine

Unlike C1 and C2, the osteology of the five subaxial vertebrae share much in common. Each consists of a vertebral body anteriorly, which are separated by an intervertebral disc, bilateral transverse processes containing a foramen, pedicles, as well as two facet joints and a spinous process posteriorly. The subaxial spine, much like the entirety of the vertebral column, is to resist the compressive loads that are placed upon it. Additionally, the bony structures of the cervical spine act to protect important neurovascular structures and provide stability while allowing for functional flexion, extension, and lateral bending (Fig. 4a, b).
Fig. 4

(a, b) Axial and lateral representations of a subaxial cervical vertebra. (From: Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body, Plate 84–85, Public Domain)

Vertebral Body

The anterior aspect of the vertebra is a relatively cylindrical structure called the vertebral body. The body withstands the majority of the compressive loads placed on the vertebral column, and each is separated by an intervertebral disc that functions as a shock absorber. With descending levels down the spinal column, the height of the body slightly increases in height, with the occasional exception of C6, which can be shorter than C7. Each level is larger in the coronal plan than in the sagittal plane. The diameter of each body in the coronal plane is larger than that in the sagittal plane. The superior aspect is concave, and the inferior aspect is convex. Both the superior and inferior aspects contain a shell of cortical bone called the end plate, which eventually transitions into the fibrocartilaginous intervertebral disc. In the coronal plane, the lateral superior aspects of the body demonstrate a lip of bone that projects cranially is congruent with the inferior and lateral aspects of the adjacent cranial body and make up the uncovertebral joint, or joint of Luschka. The uncovertebral joint is important in resisting lateral translation of the vertebra and helps limit lateral bending. Intraoperatively, the uncovertebral joints are important anatomical landmarks that aid in identifying the lateral extent of the body and can act as a reference point for identifying the midline when placing implants during anterior-based procedures.

Pedicles

Projecting dorsolaterally each side of the body is the pedicle, which connects the body to the posterior arch. Unlike the pedicles of the thoracic and lumbar regions, those in the subaxial spine are located midway between inferior and superior end plates of the body on the coronal plane. Descending down the subaxial spine from C3 to C7, the pedicle height increases from an average 5.1 to 9.5 mm, and width increases from 3 to 7.5 mm. Average width and height increase from 5 to 7 mm, respectively (An et al. 1999; Ebraheim et al. 1997; Panjabi et al. 1991b). Additionally, the pedicle angle transitions from 45° to 30° as it descends down the subaxial spine.

Transverse Process

Projecting laterally off of the posterior aspect of the body, anterior to the pedicle, are the bilateral transverse processes. Each transverse process contains both an anterior and posterior tubercle. The anterior tubercle is the origin of the longus colli cervicalis, anterior scalene, ventral intertransverse, and longus colli muscles. The posterior tubercle is the origin of the longissimus, levator scapulae, middle scalene, posterior scalene, splenius cervicalis, and iliocostalis muscles. The anterior tubercle of the C6 transverse process is also referred to as the carotid tubercle and is an important anatomical landmark, as it marks the transverse proves that separates the carotid artery from the vertebral artery. The transverse processes of C1 through C7 each contain a transverse foramen. The vertebral artery and vein travel through the transverse foramen of C1 through C6, and in the majority of cases, not through C7. The transverse foramen is bound by the lateral aspect of the pedicle, the posterior aspect of the anterior tubercle, and the anterior aspect of the posterior tubercle. Additionally, each transverse process contains a groove on its superior surface that runs posterior to the transverse foramen. This groove carries the exiting nerve at the corresponding level after it exits the neural foramen. For example, the groove on the C3 transverse process contains the exiting C3 nerve root.

Facet Joint

Projecting from both the superior and inferior aspects of the lateral mass is an articular process that is congruent with the adjacent articular process of the neighboring vertebra, which together comprises the facet joint. The superior articular process of the vertebra articulates with the inferior articular process of the cephalad vertebra, and the inferior facet of the vertebra articulates with the facet of the superior articular process of the caudal vertebra. The facet joint is a diarthrodial joint with a relatively lax capsule that allows for appropriate motion to occur. In the sagittal plane, these joints are oriented obliquely from anterior-superior to posterior-inferior at approximately 45° (Fletcher et al. 1990). This orientation differs from the relatively vertically oriented facet joints in the coronal plane of the lumbar spine, and in conjunction with the relatively lax capsule, allows for a broad range of motion in flexion, extension, lateral bending, and rotation (Bland 1987). Just as in other diarthrodial joints throughout the body, the facet joint is susceptible to degenerative changes such as joint swelling, cartilage thinning, and osteophyte formation. Given its close proximity to the neural foramina and spinal canal, these changes can have significant clinical implications.

Spinal Canal

The cervical spinal canal is bordered ventrally by the posterior aspect of the vertebral body, ventrolaterally by the pedicles transverse near the location of the neural foramina, laterally by the lateral masses, and posteriorly by the lamina and spinous process. The lateral diameter of the spinal canal is larger than the anterior-posterior (AP) diameter at all levels of the subaxial spine. The AP diameter is approximately 17 mm at the C3 level and decreases to 15 mm at C7, which has the lowest cross-sectional area.

Lateral Mass

Located dorsolateral to the pedicle is a cylindrical piece of bone termed the lateral mass. The lateral mass is analogous to the pars interarticularis of the thoracic and lumbar spinal regions, as it is the structure that connects the superior and inferior articular surfaces that make up the cephalad and caudal facet joints. It is directly dorsal to the midportion of the transverse process, and as such it is in very close proximity to the exiting nerve root. It has a bony projection dorsomedially, which becomes confluent with the lamina. The lateral masses of the subaxial cervical spine have an average depth and width of approximately 13 mm and 12 mm, respectively, and slightly decrease at each descending level to C7 where it is thinnest (Mohamed et al. 2012). Given the relatively small pedicle size in this region of the spine, screw fixation within the lateral mass is sometimes a desired treatment option, and thus a proper understanding of the lateral mass size is crucial in avoiding complications.

Lamina and Spinous Process

The dorsomedial projection from the lateral masses is termed the lamina. As they continue posteriorly bilaterally, they merge to form the posterior-most bony prominence called the spinous process. The C2 through C6 vertebra are normally bifid, but the C7 spinous process is not. The lamina and the spinous process make up the posterior aspect of the spinal canal. An important anatomic landmark is the junction of the lamina and spinous process posteriorly.

Ligaments

The subaxial cervical spine contains an array of ligaments. The ligaments contribute significantly to the stability and alignment of the bony structures in the region and allow for motion in various planes while restricting extremes of motion that could compromise proper anatomic alignment and integrity of the local structures.

The anterior and posterior aspects of the vertebral bodies and intervertebral discs are bound by both the anterior and posterior longitudinal ligaments. The anterior longitudinal ligament (ALL) is composed of longitudinal fibers that run in a cranial and caudal direction spanning the base of the skull to the sacrum. The ALL attaches to the anterior surfaces of the vertebral bodies and intervertebral discs and acts as a restraint to hyperextension of the mobile segments of the vertebral column. The ALL is narrow and thick over the concave surface of the vertebral bodies but becomes more wide and thin over the discs. The posterior longitudinal ligament (PLL) also spans the length of the vertebral column, fanning out to form the tectorial membrane at its most cranial aspect, and attaches to the sacrum caudally. Just like the ALL, the PLL is more narrow over the bodies and wide over the discs (Parke and Sherk 1989) (Fig. 1).

The ligamentum flavum is a grouping of sequential ligaments located in the posterior segment of the vertebra, with the name arising from the relatively yellow appearance (Fig. 5). Each ligament traverses adjacent lamina, attaching anteriorly near the midportion of the cephalad lamina and running obliquely to attach to the superior most margin of the caudal lamina. These ligaments have a high elastin content that have the propensity to lose their elasticity along with the aging process. In such situations, anterior buckling of the ligaments may occur during extension which may in turn produce a mass effect in the spinal canal and contribute to spinal cord compression.
Fig. 5

Posterior representation of the upper cervical vertebra. (From: Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body, Plate 305, Public Domain)

The ligamentum nuchae is composed of the interspinous and supraspinous ligaments. The interspinous ligament is a relatively thin structure that connects the spinous processes of adjacent vertebra. It runs obliquely from the anteroinferior aspect of the cephalad spinous to the posterosuperior aspect of the caudal spinous process. It is bound by the ligamentum flavum anteriorly and the supraspinous ligament posteriorly. The supraspinous ligament connects the posterior tips of the spinous processes along the length of the vertebral column. However, in the subaxial spine, these two ligaments are less distinct as individual structures until the level of C7 but rather form a complex of thick ligamentous elastic tissue that is referred to the ligamentum nuchae. The ligamentum nuchae runs from the inion of the occiput to the spinous process of C7 and acts as an attachment point for the nuchal musculature in the region.

Intervertebral Disc

The cervical spine contains six intervertebral fibrocartilaginous discs which separate the vertebral bodies (Fig. 1). There is no disc between the occiput and the atlas or between the atlas and the axis. The first disc is located between C2 and the C3 body. The junction of the disc with the adjacent bodies is lined by a cartilaginous layer termed the end plates. The disc itself is composed of two primary components – the nucleus pulposus and the annulus fibrosus. The nucleus pulposus is the centrally located portion of the disc that is the remnant of the primitive notochord and is comprised with primarily type II collagen, proteoglycans, and water. This makeup of the nucleus pulposus results in a gelatinous type substance that allows for force dissipation to the annulus fibrosis and both end plates when compression is applied to the vertebral column. The annulus fibrosus is the component of the disc that surrounds the nucleus pulposus circumferentially and composed of type I collagen, proteoglycans, and water. It is characterized by multiple circumferential layers of fibers that run in an oblique pattern from the cephalad to caudal vertebral bodies. The annulus fibrosus has a high tensile strength that contributes to the stability within a pair of vertebra, which is assisted in the lateral direction by the uncovertebral joint. As the aging process progresses, the margin between the nucleus pulposus and annulus fibrosus becomes more difficult to distinguish (Bland and Boushey 1990). In the coronal view, the superior aspect of the disc is concave, and the inferior aspect is convex as to contour its respective adjacent end plates. The height of the intervertebral disc is slightly larger anteriorly than posteriorly, which contributes to the lordotic curvature of the cervical spine.

Fascia

Investing

The deep cervical layer of the neck is separated into compartments that can be used as landmarks during dissection. The investing layer is the most superficial layer and provides broad coverage to the trapezius posteriorly and wraps around anteriorly to enclose the sternocleidomastoid (SCM) as well. Superiorly, it reaches the hyoid bone and the caudal extent of the mandible and then dives inferiorly to capture both the suprasternal space and form the ceiling of both the ventral and dorsal cervical triangles (Fig. 6).
Fig. 6

Axial cuts of the neck at the level of the sixth cervical vertebrae demonstrating fascial arrangements: investing fascia (red), prevertebral fascia (purple), pre-tracheal fascia (yellow). (By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body: Gray’s Anatomy, Plate 384, Public Domain)

Pre-tracheal

The next layer is the pre-tracheal layer, which houses many structures and likewise is referred to by multiple names including the middle cervical fascia or the visceral layer. This multifaceted aponeurosis envelops the infrahyoid muscles as well at the omohyoid muscles which lie just superficial to the visceral space. This space is residence to important soft tissue structures such as the thyroid gland, larynx, trachea, and esophagus and deep to this layer run the thyroid vessels. Its superior attachments are the hyoid and thyroid cartilage and inferiorly to the clavicles and sternum. The carotid sheath makes up its lateral margin (Fig. 6).

Prevertebral

The prevertebral layer is a thick fascial plane that surrounds the vertebral column and its muscles. This layer includes the longus and the scalene muscles. The longus colli is a notable structure that aids in establishing midline during an anterior cervical approach. Identifying this structure also helps protect the cervical portion of the sympathetic chain during anterior dissection by retracting laterally. The alar layer is also included as part of the prevertebral layer and encloses the carotid sheath, which houses the vagus nerve, carotid artery, and internal jugular vein (Fig. 6).

Muscles

Ventral

The anterior cervical muscles can be divided into superficial and deep. The platysma is the most superficial layer and is a thin wispy muscle that begins from the mandible spreading inferiorly and laterally to the second rib and acromion process. It has neurovascular bundles that integrate into the skin with its main function aiding in facial expression. Just below this lies the sternocleidomastoid (SCM) which has two heads of origin: the medical clavicle and the sternum that attach to the mastoid and occipital bones. It runs obliquely and functions to turn the head the contralateral side as well as flexion to the ipsilateral side (Fig. 7). It also separates the neck into different triangles, its contents which will be discussed later.
Fig. 7

Superficial ventral muscles of the neck. (By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body: Gray’s Anatomy, Plate 386, Public Domain)

The next layer of muscles is the infrahyoid, scalene, and longus group. The infrahyoid muscles are a group of muscles, as the name implies, that attach to the hyoid bone. These include the mylohyoid, stylohyoid, geniohyoid, digastric, and omohyoid. The strap muscles of the larynx are the sternothyroid and sternohyoid which are important structures to landmark during an anterior approach because they have no direct involvement in cervical motion. The scalene group is made up of the anterior, medial, and posterior scalene muscles. The anterior muscle originates from the transverse process of the C3 to C6 vertebrae and inserts into the first rib. The medial arises from the posterior transverse process of C2 to C7 and also inserts on the first rib. The posterior scalene muscle has more variable course but originates from the posterior transverse process of C4 to C6 and inserts onto the second rib. This muscle group is well-known for its contribution to thoracic outlet syndrome, which results from neurovascular compression of either the subclavian artery or brachial plexus. The longus muscle group is composed of the longus colli, capitis, and rectus lateralis and as previously discussed are found within the prevertebral fascia. The longus colli originates from the anterior aspect of C3 to C6 and extends obliquely from C1 to T3 to attach onto the anterior atlas. The longus capitis arises from the anterior transverse process of C3 to C6 and attaches on the basilar aspect of the occiput. The rectus has two heads, an anterior and lateral head which originate from the lateral mass of the atlas and transverse process of the atlas, respectively. The anterior head will insert into the base of the occipital bone, while the lateral head will attach to the jugular process of the occiput (Fig. 8).
Fig. 8

Deep ventral muscles of the neck. (By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body: Gray’s Anatomy, Plate 387, Public Domain)

Dorsal

The dorsal muscle groups provide tension to the vertebrae to keep them in an upright position and deliver balance as well. These muscles are innervated by the dorsal rami. The erector muscles take advantage of the tension band principle to provide sagittal support and symmetric balance in an effort to preserve lordosis of the cervical region. Loss of strength, often attributed to pain, can lead to progressive loss of lordosis and a relative kyphotic deformity. In the coronal plane, the lateral tension bands provide support. Imbalance in any of these planes can lead to deformity seen in abnormal cervical spine curves. All the muscles in the dorsal compartment spread out into three layers discussed below.

Superficial Layer

From superficial to deep, this layer includes trapezius, splenius, and levator scapulae. These muscles work synergistically to rotate the head, extend, and laterally bend. The trapezius has a broad origin that extends along the cervical and thoracic spine. Its upper division begins at the occipital protuberance and attaches at the medial 1/3 of the clavicle. The splenius group consists of the capitis and the cervicis. The capitis begins from the ligamentum nuchae and the spinous process of C6 and inserts along the lateral 1/3 of the superior nuchal line and mastoid. The cervicis inserts along the posterior aspects of the transverse process of C1–C4. The levator scapulae originates along the same posterior tubercles of C1–C4 transverse process and insert along the medial border of the scapula between the superior medial angle and scapular spine (Fig. 9).
Fig. 9

Superficial dorsal muscles of the neck. (By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body: Gray’s Anatomy, Plate 409, Public Domain)

Intermediate Layer

This layer includes the erector spinae group which has a common original at the iliac crest, sacrum, and lumbar spinous process. These muscles consist of the iliocostalis, the longissimus, and the semispinalis from lateral to medial. They work together to extend and bend the neck in the coronal plane. The iliocostalis group inserts into the posterior tubercles of the C4–C6 transverse process; the longissimus group inserts on the mastoid process. The semispinalis group inserts along the spinous process of the cervical spine (Fig. 10).
Fig. 10

Intermediate and deep dorsal muscles of the neck. (By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body: Gray’s Anatomy, Plate 389, Public Domain)

Deep Layer

The transversospinalis group makes up the deepest layer and lies along the spinous process and lamina of the cervical spine. They consist of the multifidus and rotator muscles. They are innervated by the dorsal rami of the spinal nerves of the cervical spine (Fig. 10).

Neurovascular Structures

Spinal Cord

Though a detailed description of spinal cord neuroanatomy is beyond the scope of this chapter, basic anatomic understanding is necessary. The spinal cord exits the intracranial space through the foramen magnum and terminates at approximately L2 as the conus medullaris. The spinal cord is widest at C6, measuring an average of 38 mm in circumference, which provides enough space for the increased density in neurologic structures such as the brachial plexus (Parke and Sherk 1989). The inner cord is made up gray matter which houses the nerve cell bodies and branching dendrites. It is separated into anterior, lateral, and posterior segments (horns). The anterior horn contains motor neurons controlling the skeletal muscles and is the column where the cell bodies of the alpha motor neurons are located. The posterior horn contains sensory neurons that transmit sensory information from the body that includes fine touch, proprioception, and vibration (Fig. 11). The lateral segment is located only within the thoracic and upper lumbar regions and contains components of the sympathetic nervous system.
Fig. 11

Transverse section through cervical spinal cord with labeled anterior and posterior horns of the inner gray matter. (From: Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body, Plate 666, Public Domain)

The outer circumferential layer is the white matter and is composed of myelinated axons. In a similar manner to the gray matter, it is separated into posterior, lateral, and anterior columns. The lateral column houses the lateral corticospinal tract which provides efferent motor innervation control ipsilateral extremity motion. Also within the lateral column is the lateral spinothalamic tract which is sensory pathway that transmits contralateral pain and temperature. This tract decussates to the other side of the spinal cord at the anterior white commissure, usually 1–2 spinal nerve segments above the entry point. The posterior column, composed of the fasciculus gracilis and cuneatus, is the structure responsible for ascending sensory signals transmitting proprioception, vibration, and fine touch. Sensory information from this pathway is also from the contralateral extremity although its crossover is much higher, located in the brain stem. The anterior column houses both sensory and motor systems, as well as the anterior spinothalamic tract which is responsible for crude touch.

Meninges and Dura

The meninges enclose the spinal cord and are composed of three layers: the pia, arachnoid, and dura matter. The innermost layer is the pia, followed by the arachnoid and then the dura mater. The pia has lateral projections between exiting nerves that attach to the arachnoid and dura. These projections are known as the denticulate ligaments and with the aid of CSF act as a bolster for the spinal cord. The space between the pia and arachnoid is known as the subarachnoid space and contains CSF and nerve rootlets. The space between the dura and vertebral canal is the epidural space and has a rich venous plexus and adipose tissue (Fig. 12).
Fig. 12

Transverse section through cervical spine with labeled membranes and spinal nerve roots. (From: Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body, Plate 770, Public Domain)

Nerve Roots

In the cervical spine, there are eight rootlets that exit the spinal cord that unite and form the dorsal and ventral roots. These form nerve roots at each corresponding level and pass through the dura to the intervertebral foramina. In the cervical spine, the nerve roots pass above the corresponding pedicle, except for the C8 nerve root which travels underneath the C7 pedicle. These nerves also leave the spinal cord at an angle that approximates a right angle and explains why foraminal and central herniations will affect the same nerve root. In the foramen, the nerve root takes up one-third of the space, medially it is located at the caudal portion of the superior articular process and as it travels laterally adopts a more inferior position above the pedicle (Daniels et al. 1986). When the neck is extended, the foramen size decreases in overall volume, and the nerve takes up a more superior position within the foramen; when flexed, the foramen size increases, and the nerve root assumes a position in the caudal half of the foramen (Rauschning 1991). The remaining space is filled with fat, which provides cushion to the nerve (Flannigan et al. 1987).

Spinal Cord Blood Supply

The vertebral arteries are the primary blood supply to the cervical spine which branch of the subclavian arteries and ultimately form the basilar artery. In general, each vertebral artery enters the transverse foramen at C6 and courses rostrally until C1 (Rickenbacher et al. 1982). It is important to note, during an anterior approach that the vertebral artery is located in the middle one-third of the vertebral body, just lateral to the uncinated process. At the atlas, the vertebral arteries curve around and enter the foramen magnum to unite with the contralateral artery to become the basilar artery. Throughout their course, they give off feeding branches to the spinal cord known as the anterior and posterior spinal arteries. The anterior spinal artery supplies the anterior two-thirds of the spinal cord, while the posterior spinal artery assumes the remaining one-third.

Venous outflow of the spinal cord consists of three anterior and three posterior veins. The most prominent are the anterior venous structures and are located medial to the pedicles. The posterior venous plexus surrounds the spinal cord.

Important Ventral Structures

Carotid Sheath

The carotid sheath contains the internal jugular vein, the vagus nerve, and the common carotid artery from lateral to medial. A small branch of the hypoglossal nerve can sometimes be seen crossing anteriorly. The common carotid artery branches approximately 1 cm above the superior border of the thyroid cartilage within this triangle. The carotid sinus lies just inferior to the bifurcation and is prominent baroreceptor regulating blood pressure. The vagus nerve, lying just dorsal, gives off two important branches to the neck: the superior and inferior laryngeal nerves (Fig. 13).
Fig. 13

Relevant ventral structures of the neck. (By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body: Gray’s Anatomy, Plate 794, Public Domain)

Vertebral Artery

The vertebral artery is divided into four segments and has an average diameter of 4.5 mm. It travels medial to the anterior scalene muscles and enters the C6 foramen in roughly 90% of the population. After entering cranially through the foramen transversarium of C2 and C1, it then changes course and heads medially along the superior arch of C1 at which point it goes further cranially into the foramen magnum. During a posterior approach to C1, it is critical to avoid dissection greater than 1.5 cm lateral to the midline as injury to the vertebral artery is greatest in this region (Fig. 14).
Fig. 14

Internal carotid and vertebral arteries. (By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body: Gray’s Anatomy, Plate 513, Public Domain)

Superior Laryngeal Nerve

A branch off the vagus nerve, the superior laryngeal nerve runs medial to the carotid sheath and bifurcates at the level of the hyoid to provide motor function the inferior pharyngeal constrictors. It also has sensory branch that provides sensation to the base of the tongue and the larynx. Injury to this nerve can be manifested with poor gag reflex and voice control especially with high pitches. Loss of the gag reflex can be most debilitating as these patients are often at increased risk for aspiration.

Inferior (Recurrent) Laryngeal Nerve

The inferior laryngeal nerve, commonly known as the recurrent laryngeal nerve, has a U-shaped course in the thorax, specifically in the tracheoesophageal groove. As it pierces the inferior pharyngeal constrictor, it provides motor function to the intrinsic laryngeal muscles. Its course in the neck is not symmetric. On the left, it loops under the aortic arch, and on the right, it loops under the right subclavian artery.

Hypoglossal Nerve

The hypoglossal can be located in the carotid triangle, deep to the belly of the digastric muscle, and as previously discussed, in between the carotid artery and internal jugular vein. Before heading toward the oral cavity to innervate the tongue, it gives off a branch to innervate the strap muscles, which is termed the ansa cervicalis.

Sympathetic Chain

The sympathetic chain resides in the prevertebral fascia, just ventral to the longus colli muscles. It surrounds the vertebral artery during its ascension toward the cranial vault. Injury to this structure during an anterior approach can cause ipsilateral Horner syndrome, which is characterized by ptosis, miosis, and anhidrosis.

Surgical Anatomy: The Cervical Triangles

Ventral (4 Types)

The borders of the anterior cervical triangle are the medial edge of the SCM, the inferior mandibular border, and midline of the neck. Within this triangle reside four subtriangles. The submental triangle is formed by the hyoid and the two anterior bellies of the digastric muscles; the floor of which is made up the two mylohyoid muscles. Next is the submandibular triangle, its margins being the ventral and dorsal bellies of the digastric muscle, the inferior mandibular border with the floor consisting of the hyoglossus, mylohyoid, and middle pharyngeal constrictors muscles. Important to note, is the hypoglossal nerve which passes through this triangle. The carotid triangle is bordered by the anterior margin of the SCM, the superior border of the omohyoid and inferior border of the digastric muscle. This triangle is particularly important as the common carotid artery, internal jugular vein, and the vagus nerve are found within this structure. Last, is the muscular triangle which is formed by the medial margin of the SCM, the superior belly of the omohyoid and median plane of the neck (Fig. 15).
Fig. 15

Ventral cervical triangles: submental triangle (blue), muscular triangle (red), submandibular triangle (green), carotid triangle (yellow). (By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body: Gray’s Anatomy, Plate 386, Public Domain)

Dorsal (2 Types)

The dorsal triangle is bordered by the lateral edge of the SCM, ventral trapezius border, and middle third of the clavicle. The floor is made up the scalene muscle group and prevertebral fascia, and the ceiling is made up of the deep cervical fascia. This triangle is divided into two smaller triangles, the occipital and subclavian triangle. The external jugular vein runs caudally through this triangle at the angle of the mandible (Fig. 16).
Fig. 16

Dorsal cervical triangles: occipital triangle (orange), subclavian triangle (purple). (By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body: Gray’s Anatomy, Plate 385, Public Domain)

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Copyright information

© Springer Nature Switzerland AG 2020

Authors and Affiliations

  • Bobby G. Yow
    • 1
    Email author
  • Andres S. Piscoya
    • 1
  • Scott C. Wagner
    • 1
  1. 1.Department of Orthopaedic SurgeryWalter Reed National Military Medical CenterBethesdaUSA

Section editors and affiliations

  • Don K. Moore
    • 1
  • William C. Welch
    • 2
    • 3
  1. 1.Department of Orthopaedic SurgeryUniversity of Missouri Health CareColumbiaUSA
  2. 2.Dept. of Neurosurgery, Pennsylvania HospitalUniversity of PennsylvaniaPhiladelphiaUSA
  3. 3.Department of NeurosurgeryPerelman School of Medicine, University of PennsylvaniaPhiladelphiaUnited States

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