Download Chapter (I) Anatomy of cervical spine

Chapter (I)
Anatomy of cervical spine
Chapter (I)
Anatomy of cervical spine
The cervical spine consists of seven vertebrae, with the two upper
vertebrae; atlas (C1) and axis (C2) being atypical vertebrae and the
remaining five vertebrae (C3-C7) being classified as typical vertebrae.The
vertebral bodies of atlas and axis have unique anatomical appearances and
consequently unique biomechanical properties. In the lower cervical spine
(C3-C7) osseous elements extends posteriorly from the vertebral bodies,
consisting of pedicles , articular columns, transverse processes, laminae and
spinous processes. The primary functions of the cervical spine are to supply ,
support and mobility to the head and provide protection to the spinal cord.
(Williams & Newell, 2005).
CERVICAL VERTEBRAE: (Williams & Newell, 2005).
Cervical vertebrae are the smallest of the true vertebrae, and can be
readily distinguished from those of the thoracic or lumbar regions by the
presence of a foramen in each transverse process. The first, second, and
seventh present exceptional features; the following characteristics are
common to the remaining four (Figs. 1, 2).
The body is small, and broader from side to side than from before
backward. The anterior and posterior surfaces are flattened and of equal
depth; the former is placed on a lower level than the latter, and its inferior
border is prolonged downward, so as to overlap the upper and forepart of the
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Chapter (I)
Anatomy of cervical spine
vertebra below. The upper surface is concave transversely, and presents a
projecting lip on either side; the lower surface is concave from before
backward, convex from side to side, and presents laterally shallow
concavities which receive the corresponding projecting lips of the subjacent
vertebra.
The pedicles are directed lateral ward and backward, and are attached
to the body midway between its upper and lower borders, so that the
superior vertebral notch is as deep as the inferior, but it is, at the same time,
narrower.
The laminae are narrow, and thinner above than below; the vertebral
foramen is large, and of a triangular form.
The spinous process is short and bifid, the two divisions being often
of unequal size. The superior and inferior articular processes on either side
are fused to form an articular pillar, which projects lateral ward from the
junction of the pedicle and lamina.
The articular facets are flat and of an oval form: the superior look
backward, upward, and slightly medial ward: the inferior forward,
downward, and slightly lateral ward.
The transverse processes are each pierced by the foramen
transversarium, which, in the upper six vertebrae, gives passage to the
vertebral artery and vein and a plexus of sympathetic nerves. Each process
consists of an anterior and a posterior part. The anterior portion is the
homologue of the rib in the thoracic region, and is therefore named the
costal process or costal element: it arises from the side of the body, is
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Chapter (I)
Anatomy of cervical spine
directed lateral ward in front of the foramen, and ends in a tubercle, the
anterior tubercle. The posterior part, the true transverse process, springs
from the vertebral arch behind the foramen, and is directed forward and
lateral ward; it ends in a flattened vertical tubercle, the posterior tubercle.
These two parts are joined, outside the foramen, by a bar of bone which
exhibits a deep sulcus on its upper surface for the passage of the
corresponding spinal nerve (Williams & Newell, 2005).
Fig. (1): A typical cervical vertebra (Quoted from Gray's Anatomy, 2005)
Fig. (2): Side view of a typical cervical vertebra (Quoted from Gray's
Anatomy, 2005)
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Chapter (I)
Anatomy of cervical spine
Atypical cervical vertebrae :( Gray's Anatomy,2005 )
1.
Atlas:-
Anterior arch: forms about one-fifth of the ring: its anterior surface is
convex, and presents at its center the anterior tubercle for the attachment of
the Longus colli muscles and the anterior longitudinal ligament; posteriorly
it is concave, and marked by a smooth, oval or circular facet (fovea dentis),
for articulation with the odontoid process(dens) of the axis.
Posterior arch : The posterior arch forms about two-fifths of the
circumference of the ring: it ends behind in the posterior tubercle, which is
the rudiment of a spinous process and gives origin to the Recti capitis
posterior and the ligamentum nuchae. The diminutive size of this process
prevents any interference with the movements between the atlas and the
skull.
Lateral masses: The lateral masses are the most bulky and solid parts of the
atlas, in order to support the weight of the head. Each carries two articular
facets, a superior and an inferior arch.
Vertebral foramen
The anterior or smaller receiving
the odontoid
process of
the
axis
the posterior transmitting the spinal cord (medulla spinalis) and its
membranes
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Chapter (I)
Anatomy of cervical spine
Transverse processes
The transverse processes are large; they project laterally and
downward from the lateral masses, and serve for the attachment
of muscles which assist in rotating the head. They are long, and their anterior
and posterior tubercles are fused into one mass; the foramen transversarium
is directed from below, upward and backward. (Gray's Anatomy,2005)
2.
Axis (c2) : (Gray's Anatomy,2005)
The most distinctive characteristic of this bone is the strong odontoid
process known as the dens which rises perpendicularly from the upper
surface of the body
The dens, also odontoid process or peg, is the most pronounced
feature, and exhibits a slight constriction or neck where it joins the main
body of the vertebra. The dens is a protuberance (process or projection) of
the axis(second cervical vertebra). The condition, where the dens is
separated from the body of the axis, is called osodontoideum, and may cause
nerve and circulation compression syndrome. On its anterior surface is an
oval or nearly circular facet for articulation with that on the anterior arch of
the atlas. On the back of the neck, and frequently extending on to its lateral
surfaces, is a shallow groove for the transverse atlantal ligament which
retains the process in position. The apex is pointed, and gives attachment to
the apical odontoid ligament; below the apex the process is somewhat
enlarged, and presents on either side a rough impression for the attachment
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Chapter (I)
Anatomy of cervical spine
of the alar ligament; these ligaments connect the process to the occipital
bone.
The pedicles are broad and strong, especially in front, where they
coalesce with the sides of the body and the root of the odontoid process.
They are covered above by the superior articular surfaces.
The laminae are thick and strong, and the vertebral foramen large, but
smaller than that of the atlas.
The transverse processes are very small, and each ends in a single
tubercle; each is perforated by the transverse foramen, which is directed
obliquely upward and laterally.
The superior articular surfaces are round, slightly convex, directed
upward and laterally, and are supported on the body, pedicles, and transverse
processes.
The inferior articular surfaces have the same direction as those of the
other cervical vertebrae.
The superior vertebral notches are very shallow, and lie behind
the articular processes; the inferior lie in front of the articular processes, as
in the other cervical vertebrae
The spinous process is large, very strong, deeply channelled on its
under surface, and presents a bifurcated extremity. (Gray's Anatomy,2005)
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Chapter (I)
Anatomy of cervical spine
The Seventh Cervical Vertebrum : (Williams & Newell, 2005).
(Fig. 3)
The most distinctive characteristic of this vertebra is the existence of a
long and prominent spinous process, hence the name vertebra prominens.
This process is thick, nearly horizontal in direction, not bifurcated, but
terminating in a tubercle to which the lower end of the ligamentum nuchae is
attached.
Fig. (3): Seventh cervical vertebrum (Quoted from Gray's Anatomy, 2005)
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Chapter (I)
Anatomy of cervical spine
The transverse processes are of considerable size, their posterior
roots are large and prominent, while the anterior are small and faintly
marked; the upper surface of each has usually a shallow sulcus for the eighth
spinal nerve, and its extremity seldom presents more than a trace of
bifurcation. The foramen transversarium may be as large as that in the other
cervical vertebrae, but is generally smaller on one or both sides; occasionally
it is double, sometimes it is absent. On the left side it occasionally gives
passage to the vertebral artery; more frequently the vertebral vein traverses it
on both sides; but the usual arrangement is for both artery and vein to pass in
front of the transverse process and not through the foramen. Sometimes the
anterior root of the transverse process attains a large size and exists as a
separate bone, which is known as a cervical rib (Williams & Newell, 2005).
Intervertebral Disc: (Furman, 2010)
The intervertebral disc consists of an outer annulus fibrosus and an
inner gel-like nucleus pulposus. The intervertebral disc is thicker anteriorly,
contributing to the normal cervical lordosis. The C6-7 disc is the thickest
disc of the cervical spine.
The nucleus pulposus is the central portion of the disc, a remenant of
the notochord. It is composed primarily of glycosaminoglycans and type 2
collagen, which have the capacity to bind to large amount of water.
The nucleus pulposus is avascular and receive nutrition through
diffusion and imbibition of fluids (Bland & Boushey, 1990).
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Chapter (I)
Anatomy of cervical spine
The annulus fibrosus is formed mainly of type 1 collagen, it is a
multi-laminated ligament that encompasses the periphery of the disc space.
Attaches to the end plate cartilage via collagen fibers which run obliquely to
the vertebral body and in opposite direction to the annular fibers of the
adjacent layer. The annulus is also attached to the apophyseal ring and
blends centrally with the nucleus pulposus. Its outer one third has been
found to be innervated by the sinuvertebral and the vertebral nerves.
The end plates of the vertebral bodies are lined with hyaline cartilage
and bind the disc to the vertebral body.
The adult cervical disc has a crescentic shape anteriorly, with the apex
of the crescent at the uncovertebral joints on each side. The posterior
annulus has multiple vertical fissures. In addition, the nucleus of the cervical
disc tends to be poorly centralized when compared with the lumbar disc. In
the lumbar disc, the nucleus tends to be well localized in the center of the
disc, and the posterior annulus tends to remain relatively intact when
compared with the cervical disc (Furman, 2010).
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Chapter (I)
Anatomy of cervical spine
Fig. (4): Interverteberal disc (Quoted from Furman, 2010)
cervical spine facet joint: (Furman, 2010)
The lower cervical spine (C3-C7) facet joints are arranged in pairs
bilaterally and each joint consist of opposing articular facets, i.e. the inferior
articular process (IAP) of the vertebra above and the superior articular
process (SAP) of the vertebra below (Figure 5). The facets are oriented
slightly oblique to the sagittal plane, nearly 45 degrees with the superior
articular facets facing laterally and upwards approximately to the horizontal
plane, with gradual changes in orientation in the cervico-thoracic transitional
zone. The orientation of these facets allows flexion, extension, lateral
bending and rotation of the lower cervical spine.
Immediately anterior to each facet joint the 8 cervical spine nerves
root exits the spinal canal through the intervertebral foramen formed by the
pedicles, vertebral bodies and uncinate processes, intervertebral disc and the
articular column.
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Chapter (I)
Anatomy of cervical spine
Fig. (5): Facet joint Orientation (Quoted from Furman, 2010)
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Chapter (I)
Anatomy of cervical spine
Intervertebral Neural Foramina:
The lateral portion of the spinal canal is covered posteriorly by the
lateral aspects of a superior and inferior lamina. Ventral to the lamina, the
ligamentum flavum is attached the two-thirds of the undersurface of the
superior lamina, but inferiorly it is attached only to the superior edge of the
lower lamina. Laterally, the ligamentum flavum ends 1 to 2 mm before the
medial limit of the neural foramen.
The anterior boundary of the cervical neural foramen, from rostral to
caudal, is the posterolateral cortical margin of the superior vertebral body,
the intervertebral disc covered by the posterior longitudinal ligament (PLL),
and a small portion of the posterolateral cortical margin of the inferior
vertebral body and its uncinate process. Posteriorly, from rostral to caudal,
the neural foramen is bounded by 1 to 2 mm of the superior (descending)
facet, followed by the entire ventral surface of the inferior (ascending) facet.
The superior and inferior boundaries of the neural foramen are formed by
the superior and inferior vertebral pedicles, respectively (Russell and
Benjamin, 2004) (Fig.6).
Fig. (6): A, axial CT scan through the neural foramen. B, a sagittal reformatted CT scan through
the cervical neural foramen (Russell & Benjamin, 2004)
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Chapter (I)
Anatomy of cervical spine
Ligaments and Muscles of Posterior Cervical Spine: (Macgregor &
Mior, 1989).
The functions of a ligament are: (1) to provide stability to the joint, (2)
to absorb energy during trauma, and (3) to act as a joint position transducer
during physiologic motions. Ligaments, along with the paracervical muscles
in the cervical spine, prevent motion between vertebrae that might injure the
spinal cord or nerve roots. The cervical spine ligaments have numerous and
complex interrelationships (Fig. 7).
Running vertically along the anterior and posterior aspects of the
vertebral bodies, the anterior and posterior longitudinal ligaments attach
to the discs as well. The tightly attached posterior longitudinal ligament is
thick in its central portion, which helps to prevent a disc herniation from
pressing directly on the cord posteriorly, It also limits flexion and
distraction.
The interspinous and supraspinous ligaments are also located
posteriorly but the interspinous ligaments are not as well developed in the
cervical region. The supraspinous and inter-spinous ligaments limit flexion
and anterior horizontal displacement.
The ligamentum flavum, a yellowish elastic membrane, overlies the
space between the laminae of adjacent vertebrae and the neural arches. The
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Chapter (I)
Anatomy of cervical spine
posterior location of the ligamentum flavum helps to restrain hyperflexion.
The ligamentum flavum becomes shortened and thicker in hyperextension
and elongated and thinner in hyperflexion. During hyperextension, it may
protrude into the cervical canal as much as 3.5 mm. Impingement on the
spinal cord during extension is normally prevented by the elastic properties
of the ligament; however, hypertrophy of the ligamentum flavum or loss of
elasticity through degeneration may lead to canal narrowing or cord
impingement.
The capsular ligaments, oriented approximately orthogonal to the
articular facets, provide maximal mechanical efficiency in resisting
distraction of the facets but relatively poor resistance to shear (Macgregor &
Mior, 1989).
Fig. (7): Ligaments of cervical spine (Quoted from Furman, 2010)
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Chapter (I)
Anatomy of cervical spine
Muscles of the Posterior Cervical and Upper Thoracic Spine
The trapezius muscle forms the most superficial layer of the muscles
of the back of the neck, which largely originates from the thoracic spinous
processes and the ligamentum nuchae. The splenius cervicis and splenius
capitis muscles are deep to the trapezius, forming the second layer, they are
attached to the cervical transverse processes and the mastoid process
respectively. The third layer is formed by the following deep muscles:
 Semispinalis Capitus (head rotation/pulls backward).
 Iliocostalis Cervicis (extends cervical vertebrae).
 Longissimus Cervicus (extends cervical vertebrae).
 Longissimus Capitus (head rotation/pulls backward).
 Longissimus Thoracis (extension/lateral flexion vertebral column, rib
rotation).
 Iliocostalis Thoracis (extension/lateral flexion vertebral column, rib
rotation).
 Semispinalis Thoracis (extends/rotates vertebral column).
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Chapter (I)
Anatomy of cervical spine
(Furman, 2010) Table (1): Function and innervations of cervical spine muscles
(Junwei et al., 2003)
CERVICAL MUSCLES
Sternocleidomastoid
FUNCTION
Extends & rotates head, flexes
vertebral column
Scalenus
Flexes & rotates neck
Spinalis Cervicis
Extends & rotates head
Spinalis Capitus
Extends & rotates head
NERVE
C2, C3
Lower cervical
Middle/lower
cervical
Middle/lower
cervical
Extends & rotates vertebral
Middle/lower
column
cervical
Semispinalis Capitus
Rotates head & pulls backward
C1 – C5
Splenius Cervicis
Extends vertebral column
Longus Colli Cervicis
Flexes cervical vertebrae
C2 – C7
Longus Capitus
Flexes head
C1 – C3
Rectus Capitus Anterior
Flexes head
C2, C3
Rectus Capitus Lateralis
Bends head laterally
C2, C3
Iliocostalis Cervicis
Extends cervical vertebrae
Semispinalis Cervicis
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Middle/lower
cervical
Middle/lower
cervical
Chapter (I)
Anatomy of cervical spine
Longissimus Cervicis
Extends cervical vertebrae
Longissimus Capitus
Rotates head & pulls backward
Rectus Capitus Posterior
Middle/lower
cervical
Middle/lower
cervical
Extends & rotates head
Suboccipital
Extends head
Suboccipital
Obliquus Capitus Inferior
Rotates atlas
Suboccipital
Obliquus Capitus Superior
Extends & bends head laterally
Suboccipital
Major
Rectus Capitus Posterior
Minor
The Nuchal Ligament:
The nuchal ligament is an intervertebral syndesmosis, a bilaminar
fibro-elastic inter-muscular septum interposed between the paired groups of
paravertebral muscles of the cerviconuchal region. It extends from the
external occipital protuberance to the spinous process of C7, continuing
below C7 as the interspinous ligament in the thoracic region. It is a strong
fibrous band covered by the multiple layers of the superficial and deep
cervical fascias and by the aponeurosis of the trapezius muscle. (Honet &
Puri, 1979).
Functionally, this ligament is important for maintaining the lordotic
alignment of the cervical spine and stabilizing the head during rotation of the
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Chapter (I)
Anatomy of cervical spine
cervical spine. It is a reliable landmark and widely advocated as a means to
assure a midline orientation. The nuchal ligament has funicular (dorsal) and
lamellar (ventral) portions
This ligament is best surgically used for bloodless, non disruptive
surgical exposure of cervical spine (Honet & Puri, 1979).
Nerve Supply:
There is an intricate nerve supply to the cervical spine. Nerves from
the cervical and brachial plexus divide in branches supplying the cervical
spine bones, ligaments, intervertebral discs, muscles and other soft tissues in
a segmental organization. Autonomic fibers, relaying in the cervical
sympathetic ganglion and coursing with the vasculature as well as arising
from the spinal nerves, also supply some of the cervical spine structures.
(Versteegen et al., 2000).
At each spinal segment the recurrent spinal meningeal nerve
(sinuvertebral nerve) of Luschka re-enters the spinal canal via the foramen
in order to supply the outer part of the intervertebral disc with sensory and
sympathetic autonomic fibers. The nociceptors and mechanoreceptors in the
annulus fibrosus mediate pain transmission from structural disruption of the
intervertebral disc itself or from the chemically mediated inflammatory
effect of phospholipase A2. Pacinian corpuscles and Golgi tendon organs
present in the posterolateral region of the outer one third of the annulus
transmit proprioceptive information from the intervertebral disc (Versteegen
et al., 2000).
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Chapter (I)
Anatomy of cervical spine
The medial branches and accessory nerves of the primary dorsal
rami supply the articular structures including the capsule and synovial folds,
but not the articular cartilage, with nociceptive fibers and mechanoreceptive
nerve endings at a segmental organization. Each medial branch curves the
ipsilateral articular column and sends ascending and descending branches to
the joints above and below. (Bland & Boushey, 1990).
The sinuvertebral nerve arises from the ventral ramus (somatic
root), whereas the vertebral nerve (autonomic root) is derived primarily from
the sympathetic nervous system. However, the vertebral nerve has
connections with the cervical ventral rami, which suggests the possibility of
the vertebral nerve also conveying somatic afferents from the disc (Bland &
Boushey, 1990).
Blood Supply:
The blood supply to the cervical spine arises primarily from the
brachio-cephalic trunk, the common carotid arteries and the vertebral
arteries. Spinal and muscular branches supply the vertebral bodies, the
posterior elements and the adjacent musculature of the posterior part of the
cervical spine (Williams & Newell, 2005).
The spinal and accessory branches of the vertebral arteries
anastomose longitudinally and course the intervertebral foramen where they
continue as anterior and posterior radicular arteries with vascular supply to
the facet joints, spinal cord and posterior elements of the spinal column and
are surrounded by the accessory vertebral vein. Arteries of the back of the
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Chapter (I)
Anatomy of cervical spine
neck include muscular branches of the vertebral artery, occipital and deep
cervical arteries as well as radicular and muscular branches of the ascending
cervical artery (MacLain, 1994).
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