Structure and Function of the Vertebral Column

Structure and Function of the Vertebral Column

The spine, or vertebral column, consists of 33 vertebral segments, divided into 5 regions: cervical, thoracic, lumbar, sacral, and coccygeal. Normally, there are 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal segments. The sacral and coccygeal segments are fused in the adult, forming individual sacral and coccygeal bones. This text focuses primarily on the kinesiology of the cervical, thoracic, and lumbar regions. Each of these three regions allows flexion and extension, lateral flexion, and horizontal plane (axial) rotation. The amount of motion allowed at any particular region is largely dictated by the shapes and functions of local bony, muscular, and ligamentous structures. The movement that occurs between two vertebrae is typically only a few degrees; however, when added across several vertebrae, the motion allowed at any particular region can be quite substantial.

Disease, trauma, or reaching an advanced age can lead to a host of neuromuscular and musculoskeletal problems that involve the spine. These problems may be associated with pain or other impairments because of the close anatomic relationship among the spinal cord, nerve roots, bony structures, and connective tissues of the vertebral column. For example, a herniated (bulging) intervertebral disc can press on adjacent nerve roots, causing pain, weakness, and reduced reflexes. Furthermore, poor posture and certain movements of the spinal column can increase the likelihood of impinging the adjacent neural structures.

This chapter presents an overview of the important anatomic structures and kinematic interactions required for normal posture and spinal motion. This material is intended to serve as a sound basis for understanding common impairments of the back and neck, as well as the rehabilitation principles involved in treatment of these conditions.

Normal Curvatures

The human vertebral column is composed of a set of natural curves, as is illustrated in Figure 8-1. These reciprocal curves are responsible for the normal resting, or neutral, posture of the spine. The cervical and lumbar regions display a natural lordosis, or slightly extended posture, in the sagittal plane. In contrast, the thoracic and sacrococcygeal regions exhibit a natural kyphosis, or slightly flexed, posture. The anterior concavity of the thoracic and sacral regions provides space for important vital organs within the chest and pelvis.

The natural curvatures of the vertebral column are not fixed; they are dynamic and flexible to accommodate a wide variety of different postures and movements (Figure 8-2). For example, extension increases the lordosis of the cervical and lumbar regions but reduces the thoracic kyphosis (Figure 8-2, B). Flexion, in contrast, reduces the lordosis of the lumbar and cervical regions and accentuates the kyphotic curve of the thoracic region (Figure 8-2, C).

The normal curvatures of the spine provide strength and stability to the entire axial skeleton. It is interesting to note that a vertebral column that possesses these natural curves can support greater compressive force than one that is straight. When these natural curvatures are maintained, compressive forces can be shared by the tension produced from the stretched connective tissues and muscles located along the convex side of each curve. Also, the flexible nature of the spinal curvatures allows the vertebral column to “give” slightly under a load, rather than support large forces statically.

Disease, trauma, genetically loose ligaments, or habitual poor posture can lead to an exaggeration (or reduction) of the normal spinal curvatures. These variations of natural spinal curves can stress the local muscles and joints, and can reduce the volume in the thorax for expansion of the lungs.

Line of Gravity

Although highly variable, the line of gravity acting on a person with ideal posture passes through the mastoid process of the temporal bone, anterior to the second sacral vertebrae, slightly posterior to the hip, and slightly anterior to the knee and ankle (Figure 8-3). As indicated in Figure 8-3, the line of gravity courses just to the concave side of each vertebral region’s curvature. Consequently, in ideal posture, gravity produces a torque that helps maintain the optimal shape of each spinal curvature, allowing one to stand at ease with minimal muscular activation and minimal stress on surrounding connective tissues. These ideal biomechanics significantly reduce the energy of maintaining postures such as standing and sitting.

Many persons exhibit poor posture as a result of muscular tightness or weakness, trauma, poor habit, body fat distribution, disease, or heredity. Figure 8-4 displays five commonly observed abnormal or “faulty” postures. Over time, these postures may significantly destabilize the spine, requiring compensatory strategies that alter normal motion of the trunk, the extremities, or the body as a whole. For example, the swayback posture illustrated in Figure 8-4, C, is often associated with significant tightness of the lumbar extensor muscles and excessive stretch (and potentially weakness) of the abdominal muscles. This posture can increase shear forces on the intervertebral discs and joints that interconnect the lumbar spine. Clinicians who treat people with back and neck pain often attempt to correct faulty postures as a primary component of the rehabilitation process.



The cranium, or skull, is the bony encasement that protects the brain. Many of the bony features described herein serve as attachments for muscles and ligaments. Numerous other important features of the cranium are not described but are labeled in Figures 8-5 and 8-6.

The external occipital protuberance (often referred to as the “bump of knowledge”) is a palpable landmark located at the midpoint of the posterior skull, serving as an attachment for the ligamentum nuchae and the upper trapezius. The superior nuchal line is a ridge of bone that extends laterally from the occipital protuberance to the mastoid process. The inferior nuchal line resides just below the superior nuchal line, near the base of the skull. The nuchal lines provide cranial attachments for numerous muscles and ligaments.

Literally meaning “large hole,” the foramen magnum is located at the base of the skull, providing a passage for the spinal cord to meet the brain (see Figure 8-6). The prominent occipital condyles project from the anterior-lateral margins of the foramen magnum. These convex structures articulate with the atlas (first cervical vertebrae), forming the atlanto-occipital joint. Just posterior to each ear are the large, palpable mastoid processes, which serve as the cranial attachment for numerous muscles of the head and neck, most notably the sternocleidomastoid.

Typical Vertebrae

All vertebrae have several common features, many of which are evident upon examination of different views of a thoracic vertebra (Figure 8-7). The body of a vertebra is the large cylindrical mass of bone that serves as the primary weight-bearing structure throughout the vertebral column. The intervertebral disc is the thick fluid-filled ring of fibrocartilage that serves as a shock absorber throughout the vertebral column. The specific anatomy of intervertebral discs is covered in the next section. The interbody joint is formed by the junction of two vertebral bodies and the interposed intervertebral disc.

Posterior to the body of each vertebra is the vertebral canal, which houses and protects the delicate spinal cord. Pedicles are short, thick projections of bone that connect the body of the vertebrae to each transverse process. The laminae are thin plates of bone that form the posterior wall of the vertebral canal, connecting each transverse process to the base of the spinous process.

Each vertebra has matching pairs of superior and inferior articular facets. The inferior facets of one vertebra articulate with the superior facets of the vertebra below it, composing a pair of apophyseal joints. These joints, more commonly referred to as facet joints, help guide the direction of vertebral motion.

Right and left intervertebral foramina exist between adjacent vertebrae, forming passageways for nerve roots entering or exiting the vertebral column. Because the intervertebral foramen is formed between two vertebrae, spinal movement naturally alters its diameter. This important point is revisited later in this chapter.

Intervertebral Discs

Intervertebral discs play an extremely important role in absorbing and transmitting compression and shear forces throughout the spinal column. Each intervertebral disc is composed of three primary components: The nucleus pulposus, the annulus fibrosus, and the vertebral end plate (Figure 8-8).

The nucleus pulposus is the gelatinous center of the disc. Composed of 70% to 90% water, the nucleus pulposus serves as a hydraulic shock absorber, dissipating and transferring forces between consecutive vertebrae. The annulus fibrosus is composed of 10 to 20 concentric rings of fibrocartilage that, in essence, encase the nucleus pulposus. As illustrated in Figure 8-9, the rings of fibrocartilage form a crisscross pattern that strengthens the walls of the annulus. When two vertebrae are compressed from the pressure of body weight or muscular forces, the nucleus pulposus is squeezed outward, producing tension within the annulus fibrosus (Figure 8-10). This tension stabilizes the spongy disc, converting it to a stable weight-bearing structure. The vertebral end plate connects the intervertebral disc to the vertebrae above and below and helps provide the disc with nutrition.

Specifying Vertebrae and Intervertebral Discs

Individual vertebrae are numbered by region in a cranial-to-sacral direction. For example, C3 indicates the third cervical vertebrae from the top of the cervical spine. T8 indicates the eighth thoracic vertebrae (from the top), L4 describes the fourth lumbar vertebrae, and so on (see Figure 8-21 on p. 189).

Intervertebral discs are described by their position between two vertebrae. For example, the L4-L5 disc describes the intervertebral disc located between the fourth and fifth lumbar vertebrae, and the C6-C7 disc indicates the intervertebral disc between the sixth and seventh cervical vertebrae.

Spinal nerves are described in much the same way as the vertebrae. Realize, however, that cervical spinal nerves exit above their respective cervical vertebrae; in contrast, thoracic and lumbar spinal nerves exit below their respective thoracic or lumbar vertebrae.

Comparison of Vertebrae at Different Regions

Although all vertebrae have common anatomic characteristics, they also possess distinct features that reflect the unique function of a particular region. The following section, along with Table 8-1, highlights osteologic features that are specific to each region of the vertebral column.

imageTable 8-1

Osteologic Features of the Vertebral Column

  Body Superior Articular Facets Inferior Articular Facets Spinous Processes Vertebral Canal Transverse Processes Comments
Atlas (C1) None Concave, face generally superior Flat to slightly concave, face generally inferior None, replaced by a small posterior tubercle Triangular, largest of cervical region Largest of cervical region Appears as two large lateral masses, joined by anterior and posterior arches
Axis (C2) Tall with a vertical projecting dens Flat to slightly convex, face generally superior Flat, face anterior and inferior Largest and bifid (i.e., double) Large and triangular Forms anterior and posterior tubercles Contains large spinous process
C3-C6 Wider than deep; have uncinate processes Flat, face posterior and superior As above Bifid Large and triangular End as anterior and posterior tubercles Considered typical cervical vertebrae
C7 Wider than deep As above Transition to typical thoracic vertebrae Large and prominent, easily palpable Triangular Thick and prominent, may have a large anterior tubercle forming an “extra rib” Often called vertebral prominens because of large spinous process
T2-T9 Equal width and depth, costal facets for attachment of the heads of ribs 2-9 Flat, face mostly posterior Flat, face mostly anterior Long and pointed, slant inferiorly Round, smaller than cervical Project horizontally and slightly posterior, have costal facets for tubercles of ribs Considered typical thoracic vertebrae
T1 and T10-T12 Equal width and depth; T1 has a full costal facet for rib 1 and a partial facet for rib 2; T10-T12 each has a full costal facet As above As above As above As above T10-T12 may lack costal facets Considered atypical thoracic vertebrae primarily by the manner of rib attachment
L1-L5 Wider than deep; L5 is slightly wedged (i.e., higher height anteriorly than posteriorly) Slightly concave, face medial to posterior-medial L1-L4 slightly convex, face lateral to anterior-lateral; L5 flat, face anterior and slightly lateral Stout and rectangular Triangular, contains cauda equina Slender, project laterally Superior articular processes have mamillary bodies
Sacrum Fused
Body of first sacral vertebra most evident
Flat, face posterior and slightly medial None None, replaced by multiple spinous tubercles As above None, replaced by multiple transverse tubercles  
Coccyx Fusion of four rudimentary vertebrae Rudimentary Rudimentary Rudimentary Ends at the first coccyx Rudimentary  


From Neumann DA: Kinesiology of the musculoskeletal system: foundations for physical rehabilitation, St Louis, 2002, Mosby, Table 9-4.

Cervical Vertebrae

The seven cervical vertebrae are the smallest and most mobile of all vertebrae, reflecting the wide range of motion available to the head and neck (Figure 8-11).

The first two cervical vertebrae, called the atlas (C1) and the axis (C2), are unique even to the cervical region. The rest of the cervical vertebrae (C3-C7) are considered typical and are described as follows.

Typical Cervical Vertebrae (C3-C7)

The transverse processes of the cervical vertebrae possess transverse foramina (Figure 8-11, A), which serve as a protective passageway for the vertebral artery as it courses toward the brain. The small rectangular bodies of C3-C7 are bordered posteriorly-laterally by uncinate processes. The articulation of these hook-like uncinate processes with adjacent vertebrae forms the uncovertebral joints (see Figure 8-13), making this region of the cervical spine appear like a set of stackable shelves. Most of the spinous processes in the cervical region are bifid, or two-pronged, and provide attachments for muscles from both sides of the body.

Observe that the apophyseal (facet) joints throughout C3-C7 are oriented like shingles on a sloped roof in a plane that is about 45 degrees between the horizontal and frontal planes (Figure 8-11, B). This orientation has an important impact on the kinematics of this region—a point that is revisited later in this chapter.

Atlas (C1)

The Greek god Atlas is said to have supported the weight of the world on his back. The first cervical vertebra is also called the atlas, reflecting its function in supporting the weight of the cranium. The atlas is essentially two large lateral masses connected by anterior and posterior arches (Figure 8-12). Two large concave superior facets sit on top of these lateral masses to accept the large convex occipital condyles, forming the atlanto-occipital joint. Other distinguishing features include large transverse processes—the largest in the cervical region.

Axis (C2)

The axis derives its name from the large pointed projection of bone, called the dens, which literally functions as the vertical axis of rotation for rotary movements between the head and the upper cervical region (see Figure 8-12). The superior facets of the axis (C2) are relatively flat, matching the flattened inferior facets of the atlas. This conformation is well designed to allow the atlas (and head) to freely rotate in the horizontal plane over the axis, such as when the head is turned to the left or right. The bifid spinous process of C2 is broad and palpable (see Figure 8-12).

image Clinical insight

Osteophytes and Degenerative Disc Disease

Because of excessive wear, arthritis, or advanced age, some intervertebral discs become dehydrated and lose their ability to act as shock absorbers and functional spacers within the cervical region. Figure 8-13 shows a portion of the cervical spine. The disc between C3 and C4 is healthy and well hydrated and is designed to prevent bone-on-bone compression of the vertebrae. The C4-C5 intervertebral disc, however, is degenerated and almost flat. As a result, there is bone-on-bone compression of the uncinate processes, which has stimulated the formation of osteophytes (bone spurs).

Osteophytes develop in accordance with Wolff’s law, which states that “bone is laid down in areas of high stress and reabsorbed in areas of low stress.” As indicated in Figure 8-13, an osteophyte may encroach on a spinal nerve root. Most often, this results in pain and weakness throughout the peripheral distribution of the pinched nerve.

Degeneration of an intervertebral disc can also reduce the size of the intervertebral foramen; often this can cause painful impingement on the exiting nerve.

Thoracic Vertebrae

The 12 thoracic vertebrae are characterized by their sharp, inferiorly projected spinous processes and large posterior, laterally projected transverse processes. The body and transverse processes of most thoracic vertebrae have costal facets for articulation with the posterior aspect of the ribs (Figure 8-14). The anterior portion of most ribs attaches either directly or indirectly to the sternum. Therefore, the ribs, thoracic vertebrae, and sternum define the volume of the thoracic cavity. Of note is that the apophyseal joints of the thoracic vertebrae are aligned nearly in the frontal plane.

Lumbar Vertebrae

The lumbar vertebrae have massive, wide bodies, suitable for supporting the entire superimposed weight of the body (Figure 8-15). The spinous processes are broad and rectangular, connected to the body of the vertebrae through stout, thick laminae and pedicles. The facet joints of the upper lumbar region are oriented close to the sagittal plane but transition toward the frontal plane in the lower regions (L4 and L5) (Figure 8-15).


The sacrum is a triangular bone that transmits the weight of the vertebral column to the pelvis. The wide flat sacral promontory (Figure 8-16) articulates with L5, forming the lumbosacral junction. The posterior or dorsal surface of the sacrum is convex and rough, reflecting the numerous ligamentous and muscular attachments. The sacral canal (Figure 8-16) houses and protects the cauda equina (peripheral nerves extending from the bottom end of the spinal cord). Four paired dorsal sacral foramina transmit the dorsal rami of sacral nerves. On the anterior or pelvic aspect of the sacrum, four paired ventral sacral foramina (Figure 8-17) transmit the ventral rami of spinal nerves that form much of the sacral plexus.


Sometimes referred to as the tailbone, the coccyx is a small triangular bone consisting of four fused vertebrae (see Figure 8-17). The base of the coccyx articulates with the inferior sacrum, forming the sacrococcygeal joint.

Supporting Structures of the Vertebral Column

As with any other joint in the body, the joints of the spine are supported by ligaments that (1) prevent unwanted or excessive movements, and (2) protect underlying structures (Figure 8-18). Both functions are particularly important in the vertebral column because the soft and vulnerable spinal cord relies on the integrity of the vertebral column for protection. The primary supporting structures of the vertebral column are described in Table 8-2. Note that these supporting ligaments of the spine are similar to any other ligaments found in the body; they can become torn, weak, or overly shortened if held in a shortened range for a long period of time. As will be described later in this chapter, forces from activated muscle also play an essential role in stabilizing and protecting the vertebral column.

imageTable 8-2

Major Ligaments of the Vertebral Column

Name Attachments Function Comment
Ligamentum flavum Between the anterior surface of one lamina and the posterior surface of the lamina below Limits flexion Contains a high percentage of elastin; lies just posterior to the spinal cord; thickest in the lumbar region
Supraspinous and interspinous ligaments Between adjacent spinous processes from C7 to the sacrum Limit flexion Ligamentum nuchae is the cervical and cranial extension of the supraspinous ligaments, providing a midline structure for muscle attachments and passive support for the head
Intertransverse ligaments Between adjacent transverse processes Limit contralateral lateral flexion Few fibers exist in the cervical region. In the thoracic region, the ligaments are rounded and intertwined with local muscle. In the lumbar region, the ligaments are thin and membranous
Anterior longitudinal ligament Between the basilar part of the occipital bone and the entire length of the anterior surfaces of all vertebral bodies, including the sacrum Adds stability to the vertebral column; limits extension or excessive lordosis in the cervical and lumbar regions  
Posterior longitudinal ligament Throughout the length of the posterior surfaces of all vertebral bodies, between the axis (C2) and the sacrum Stabilizes the vertebral column; limits flexion; reinforces the posterior annulus fibrosus Lies within the vertebral canal, just anterior to the spinal cord
Capsule of the apophyseal joints Margin of each apophyseal joint Strengthens and supports the apophyseal joint Becomes taut at the extremes of all intervertebral motions


From Neumann DA: Kinesiology of the musculoskeletal system: foundations for physical rehabilitation, St Louis, 2002, Mosby, Table 9-3.

image Consider this…

The Cauda Equina

The caudal end of the adult spinal cord usually terminates adjacent to the L1 vertebra (Figure 8-19). The exiting lumbosacral nerves must therefore travel a great distance inferiorly before reaching their corresponding intervertebral foramina. As a group, the elongated nerves resemble a horse’s tail—hence the name cauda equina, literally meaning “horse’s tail.” Severe trauma in the lumbosacral region may damage the nerves of the cauda equina but spare the spinal cord. Because the cauda equina is composed of peripheral nerves, injury may result in muscle paralysis, atrophy, altered sensation, and reduced reflexes (hyporeflexia). Trauma to the vertebral column superior to the cauda equina (at the L1 vertebral level) is more likely to damage the (actual) spinal cord. Spinal cord injury can also cause muscle paralysis and altered sensation. In contrast to injuring peripheral nerves, however, injuring the central nerves of the spinal cord often results in spasticity and exaggerated reflexes (hyper-reflexia).

Kinematics of the Vertebral Column

By convention, movement at any spinal region is defined by the direction of motion of a point on the anterior side of the vertebrae. For example, rotation to the right indicates that the anterior side (body) of the vertebrae is rotating to the right. This can be confusing because the more visible (and palpable) spinous process rotates to the left—in the opposite direction. Furthermore, movement occurs within a plane relative to an associated axis of rotation coursing through the vertebral body (Figure 8-20).

For the sake of organization, this text examines the motions of the spine in two regions: Craniocervical and thoracolumbar. Each region permits flexion and extension, lateral flexion, and axial rotation—rotation in the horizontal plane. As introduced earlier, the motion of a particular spinal region is the summation of relatively small motions between individual vertebrae. Furthermore, these movements are guided primarily by the spatial orientation of the surfaces within the facet joints.

image Consider this…

Facet Joints Throughout the Vertebral Column: Different Orientations, Different Primary Motions

Facet (apophyseal) joints are formed by the articulation between the inferior facets of one vertebra and the superior facets of the vertebra below. The spatial orientation of the facet joints largely determines the direction and extent of motion allowed across a particular region of the vertebral column. The facet joints act like railroad tracks guiding the direction of motion of a train.

A vertebra naturally moves in the direction of least bony resistance, which is strongly dictated by the specific plane of the articular surfaces of the facet joints. This concept is useful in understanding the kinematics across the vertebral column.

Figure 8-22 shows the spatial orientation of a sample of vertebrae (indicated in red). The superior facet surfaces of the axis (C2) are oriented closest to the horizontal plane. The freest motion between C1 and C2 (atlanto-axial joint) is therefore in the horizontal plane, which occurs while turning the head fully to the left or right.

The facet surfaces of C2-C7 are oriented about halfway between the horizontal plane and the frontal plane (see Figure 8-23). This alignment allows nearly equal and ample amounts of horizontal plane rotation and lateral flexion.

The facet surfaces of thoracic vertebrae are oriented closest to the frontal plane (see Figure 8-23). This alignment would allow ample lateral flexion, but this potential for movement is limited by the attachment of the ribs.

As indicated in Figure 8-22, the facet surfaces of the upper lumbar vertebrae are oriented closest to the sagittal plane, which favors sagittal plane motions of flexion and extension. The facet surfaces of the lower lumbar vertebrae transition toward the frontal plane. This alignment favors lateral flexion and may help accommodate the natural “hip-hiking” motions that occur during walking and running. Likely more important, this near-frontal plane alignment between L5 and S1 helps prevent the lower lumbar vertebra from sliding anteriorly relative to the sacrum.

Craniocervical Region

The terms craniocervical region and neck are used interchangeably. Both terms refer to the combined set of three articulations: Atlanto-occipital joint, atlanto-axial joint, and intracervical region—referring to the cervical joints between C2 and C7. The craniocervical region is the most mobile area of the entire vertebral column. The individual joints within this region function in a highly coordinated manner to facilitate positioning of the head, which plays a large role in vision, hearing, hand-eye coordination, and equilibrium. Table 8-3 summarizes the average ranges of motion contributed by each area within the craniocervical region.

imageTable 8-3

Approximate Range of Motion for the Three Planes of Movement for the Joints of the Craniocervical Regions*

Joint or Region Flexion and Extension (Sagittal Plane, Degrees) Axial Rotation (Horizontal Plane, Degrees) Lateral Flexion (Frontal Plane, Degrees)
Atlanto-occipital joint Flexion: 5
Extension: 10
Total: 15
Negligible About 5
Atlanto-axial joint complex Flexion: 5
Extension: 10
Total: 15
35-40 Negligible
Intracervical region (C2-C7) Flexion: 35-40
Extension: 55-60
Total: 90-100
30-35 30-35
Total across craniocervical region Flexion: 45-50
Extension: 75-80
Total: 120-130
65-75 35-40


*The horizontal and frontal plane motions are to one side only. Data are compiled from multiple sources (see text) and subject to large intersubject variations.

From Neumann DA: Kinesiology of the musculoskeletal system: foundations for physical rehabilitation, ed 2, St Louis, 2010, Mosby, Table 9-7.

Flexion and Extension

Figure 8-21 illustrates an individual in full 80 degrees of craniocervical extension. Full craniocervical flexion of 45 to 50 degrees is pictured in Figure 8-23. About 25% of the total sagittal plane motion occurs through the combined motions of the atlanto-occipital and atlanto-axial joints; the remaining motion occurs across the intracervical (C2-C7) region.

The atlanto-occipital joints are well designed to produce flexion and extension because the convex occipital condyles and corresponding concave facet surfaces of the atlas fit like rockers on a rocking chair: The occipital condyles roll backward during extension (see Figure 8-21, A) and forward during flexion (Figure 8-23, A). In accordance with the arthrokinematic rules described in Chapter 1, the roll and the slide occur in opposite directions.

The atlanto-axial joint, although primarily designed for horizontal plane motion, allows about 10 degrees of extension and 5 degrees of flexion (Figures 8-21, B, and 8-23, B).

Flexion and extension of the intracervical region (C2-C7) result in an arc of motion determined by the oblique plane of the cervical facet joints. As described earlier, these joints are oriented in a plane about 45 degrees between the horizontal and frontal planes. During extension, the inferior facets of the superior vertebra slide posteriorly and inferiorly—relative to the vertebra below it (Figure 8-21, C). The mechanics of flexion are the reverse of the mechanics of extension (Figure 8-23, C).

Axial Rotation

Rotation of the head and neck in the horizontal plane is an important motion, integral to vision and hearing. As shown in Figure 8-24, the craniocervical region rotates about 90 degrees to each side, allowing nearly 180 degrees of rotational motion. With an additional 150 to 160 degrees of total horizontal plane motion of the eyes, the visual field approaches 360 degrees without moving the trunk.

The atlanto-axial joint is responsible for about half of the rotation that occurs in the craniocervical region. The vertical dens and nearly horizontal superior facets of the axis (C2) allow the ring-shaped atlas (C1) to rotate freely and securely about 45 degrees in either direction (Figure 8-24, A). Note that the head does not rotate independently of the ring-shaped atlas. The deeply seated atlanto-occipital joint strongly resists rotation; rotation of the head therefore is the result of the atlas and the attached cranium rotating as a fixed unit relative to the axis (Figure 8-24, A).

Rotation of C2-C7 is guided primarily by the oblique orientation of the facet joints. The combined motion of these joints allows about 45 degrees of rotation in either direction and is mechanically coupled with very slight amounts of lateral flexion secondary to the orientation of the facet joints (Figure 8-24, B). The arthrokinematic movements involved with rotation to the right are illustrated in Figure 8-24, B.

Lateral Flexion

The craniocervical region allows about 40 degrees of lateral flexion to each side. Although minimal, the atlanto-occipital joint contributes about 5 degrees of lateral flexion in either direction (Figure 8-25, A). Most of the motion occurs between C2 and C7.

The arthrokinematic motion between C2 and C7 is illustrated in Figure 8-25, B. Once again, this motion is guided by the 45-degree incline of the facet joints. Because of the orientation of the facet surfaces, sight horizontal plane rotation is mechanically coupled with lateral flexion.

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Flexion and Extension and the Effect on the Diameter of the Intervertebral Foramina

Intervertebral foramina allow protected passage of spinal nerves to and from the spinal cord. As the name implies, an intervertebral foramen is created by the approximation of two adjacent vertebrae. Consequently, the motion or position of either vertebra can alter the shape and therefore the size of the foramen.

Flexion increases the diameter of the intervertebral foramen; extension, in contrast, decreases it (Figure 8-26). This has clinical relevance in cases of a stenosed (narrowed) intervertebral foramen. For example, osteophyte formation within the intervertebral foramen may cause compression of a spinal nerve as it passes through this space. This can result in symptoms such as tingling, numbness, muscle weakness, reduced reflexes, and radiating pain.

Individuals with a narrowed intervertebral foramen or osteophyte formation may develop a chronically flexed neck or “forward head” posture in an attempt to alleviate pressure on the spinal nerve roots. The flexed position of the lower cervical vertebrae increases the space of the intervertebral foramen, allowing the nerves to exit with less chance of impingement.

Treatment of cervical nerve root compression often includes cervical traction with the neck in partial flexion to decompress the irritated nerve root and reduce painful symptoms.

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Forward Head Posture: Treating Poor Posture Through Active Chin Tucks

A forward head posture is one of the most commonly observed faulty postures of the craniocervical region. Typically, this posture occurs from holding the head in an excessively forward position for extended periods, as when reading a textbook resting on a table. Protraction of the head is the result of flexion of the lower cervical vertebrae and extension—and typically hyperextension—of the upper craniocervical region (Figure 8-27, A). Over time, the muscles and ligaments of the upper cervical region shorten, adapting to the close proximity of the bony structures in this area. (Note the proximity of the C1 and C2 spinous processes to the base of the skull in Figure 8-27, A.)

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Dec 5, 2016 | Posted by in MANUAL THERAPIST | Comments Off on Structure and Function of the Vertebral Column

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