Cervical Vertebrae

CERVICAL VERTEBRAE

·  The cervical vertebrae form the axial skeleton of the neck and constitute the most mobile region of the vertebral column.

·  There are seven cervical vertebrae, numbered C1 to C7 from above downward.

·  Cervical vertebrae are identified by the presence of a foramen transversarium in each transverse process.

Classification of Cervical Vertebrae

Cervical vertebrae are classified into two groups based on their structural features.

A. Typical Cervical Vertebrae

• The third, fourth, fifth, and sixth cervical vertebrae (C3–C6) are typical cervical vertebrae.
• They share common structural features.

B. Atypical Cervical Vertebrae

• The first (atlas), second (axis), and seventh (C7) cervical vertebrae are atypical.
• They possess distinctive structural features that differentiate them from typical cervical vertebrae and from one another.

TYPICAL CERVICAL VERTEBRAE

– The third to sixth cervical vertebrae (C3–C6) are classified as typical cervical vertebrae because they share similar structural features.

Features

– A typical cervical vertebra consists of the following parts:

1. Body
2. Pedicles
3. Laminae
4. Vertebral foramen
5. Spinous process
6. Articular processes
7. Transverse processes

Body

·  The body is small and wider transversely than anteroposteriorly.

·  Superior surface: It is concave from side to side and has an upward-projecting lip along each lateral margin.

·  Inferior surface: Its lateral margins are bevelled, while the anterior margin projects downward over the intervertebral disc.

·  Anterior and posterior surfaces: Both surfaces are relatively flat.

Vertebral foramen

– The vertebral foramen is large and triangular and is wider than the vertebral body.

Pedicles

·  The pedicles extend backward and laterally from the posterolateral aspects of the vertebral body.

·  They arise approximately midway between the superior and inferior borders of the body, making the superior and inferior vertebral notches nearly equal in depth.

Laminae

·  The laminae are relatively long, narrow, and thin.

·  They extend posteromedially from the articular regions and unite to form the spinous process.

Spinous process

– The spinous process is short and bifid, with its tip divided into two tubercles.

Articular processes (facets)

·  Each vertebra has two superior and two inferior articular processes.

·  Superior articular facets: These face upward and backward.

·  Inferior articular facets: These face downward and forward.

<H5>Transverse processes

·  Each transverse process is short and contains a foramen transversarium, which is a characteristic feature of cervical vertebrae.

·  Each transverse process consists of the following parts:

• Anterior root
• Posterior root
• Anterior tubercle
• Posterior tubercle
• Costotransverse bar

Development of Transverse Process

– Embryologically, each transverse process develops from two elements:

• Costal element: It forms the anterior root, anterior tubercle, costotransverse bar, and posterior tubercle.
• Transverse element: It forms the posterior root of the transverse process.

Attachments

Attachments and Relations

Body

• The anterior longitudinal ligament is attached to the anterior surface of the vertebral body near its superior and inferior margins.
• The posterior longitudinal ligament is attached to the posterior surface of the vertebral body.
• The longus colli muscle is attached to the anterior surface of the body on either side of the midline.
• The posterior surface of the body contains two or three vascular foramina for the basivertebral veins and nutrient vessels.

Laminae

– The ligamenta flava connect the laminae of adjacent vertebrae and are attached to their adjoining surfaces.

Spinous Process

– The spinous process provides attachment to several deep muscles of the neck, including:

• Interspinales cervicis
• Semispinalis cervicis
• Semispinalis thoracis
• Spinalis cervicis
• Multifidus

Transverse Process

Anterior tubercle

– The anterior tubercle provides attachment to the following muscles:

• Scalenus anterior
• Longus capitis
• Longus colli (oblique fibres)

Costotransverse bar

– Its superior surface has a groove that transmits the ventral ramus of the corresponding cervical spinal nerve.

Posterior tubercle

– The posterior tubercle provides attachment to the following muscles at different cervical levels:

• Scalenus medius
• Scalenus posterior
• Levator scapulae
• Splenius cervicis
• Longissimus cervicis
• Iliocostalis cervicis

Foramen Transversarium

– The foramen transversarium transmits the following structures:

• Vertebral artery (second part), usually through the foramina of C6 to C1.
• Vertebral veins.
• Sympathetic nerve fibres accompanying the vertebral artery, derived from the cervical sympathetic ganglia.

Ossification

– A typical cervical vertebra develops from three primary and six secondary ossification centres.

Primary Ossification Centres

• Two centres for the neural arch: One centre appears in each half of the neural arch during the 9th–10th week of intrauterine life.
• One centre for the centrum: It appears during the 3rd–4th month of intrauterine life and forms the main part of the vertebral body.
• The two halves of the neural arch unite posteriorly during the first year after birth.
• The neural arch fuses with the centrum at approximately 3 years of age.

Secondary Ossification Centres

• Six secondary ossification centres develop around puberty:
  • Two centres form the annular epiphyses along the peripheral margins of the superior and inferior surfaces of the vertebral body.
  • Two centres appear at the tips of the transverse processes.
  • Two centres develop at the tips of the bifid spinous process.
• These secondary centres gradually unite with the vertebra, and ossification is usually completed by 25 years of age.

FIRST CERVICAL VERTEBRA

• The first cervical vertebra (C1) is called the atlas because it supports the head.
• Its name is derived from Greek mythology, in which Atlas is depicted carrying the celestial sphere on his shoulders.

Features

·  The atlas is a ring-shaped vertebra without a body or spinous process.

·  It consists of the following parts:

• Anterior arch
• Posterior arch
• Two lateral masses
• Two transverse processes

Anterior arch

• The anterior arch forms the anterior part of the vertebral ring and is convex anteriorly.
• Anterior tubercle: It is a small projection located in the midline on the anterior surface of the arch.
• Facet for dens: The posterior surface of the anterior arch bears a circular articular facet for the dens (odontoid process) of the axis.

Attachments

• Anterior tubercle: It provides attachment to the longus colli muscle and anterior longitudinal ligament.
• Superior border: It gives attachment to the anterior atlanto-occipital membrane.
• Inferior border: It provides attachment to the anterior atlanto-axial membrane, which is continuous with the anterior longitudinal ligament.

Posterior arch

• The posterior arch is a curved bony structure that forms approximately two-fifths of the vertebral ring.
• Posterior tubercle: It is situated in the midline and represents a rudimentary spinous process.
• Groove for vertebral artery: A shallow groove is present on the superior surface of the posterior arch, immediately behind each lateral mass.
• This groove transmits the vertebral artery and the first cervical spinal nerve (C1).

Attachments

• Superior border: It provides attachment to the posterior atlanto-occipital membrane.
• Inferior border: It gives attachment to the posterior atlanto-axial membrane, which replaces the ligamentum flavum at this level.
• Posterior tubercle: It provides attachment to the ligamentum nuchae medially and gives origin to the rectus capitis posterior minor muscle laterally.

Lateral masses

• The atlas has two large lateral masses connected by the anterior and posterior arches. Each lateral mass presents superior, inferior, and medial surfaces and is related laterally to a transverse process.
• Superior Surface: It bears a large, concave, elongated superior articular facet that faces upward and medially. The facet articulates with the corresponding occipital condyle to form the atlanto-occipital joint. Inferior Surface: It presents an almost circular, relatively flat inferior articular facet. This facet articulates with the corresponding superior articular facet of the axis to form the lateral atlanto-axial joint.
• Medial Surface: The medial surface bears a small tubercle for attachment of the transverse ligament of the atlas. The transverse ligament holds the dens against the anterior arch and contributes to the stability of the median atlanto-axial joint.

Transverse Processes

• The transverse processes of the atlas are longer and project farther laterally than those of the other cervical vertebrae.
• Each transverse process contains a foramen transversarium for the passage of the vertebral artery, vertebral veins, and accompanying sympathetic nerve fibres.
• The transverse process has a single prominent tubercle rather than distinct anterior and posterior tubercles.

Muscular Attachments

• Rectus capitis lateralis: It arises from the superior surface of the transverse process.
• Obliquus capitis superior: It arises from the transverse process of the atlas.
• Levator scapulae: Its uppermost slip arises from the transverse process of the atlas.
• Splenius cervicis: Its uppermost fibres are inserted into the transverse process of the atlas.

Ossification

– The atlas develops mainly from three primary ossification centres, although the anterior centre commonly appears after birth.

Primary Ossification Centres

• Two lateral centres: One centre appears in each lateral mass during the seventh week of intrauterine life. Each centre extends posteriorly to form half of the posterior arch.
• One anterior centre: It usually appears during the first year after birth and forms the anterior arch.

Fusion of Ossification Centres

• The two halves of the posterior arch unite in the midline by approximately 3–4 years of age.
• The anterior arch joins the lateral masses by approximately 6–7 years of age.
• In some individuals, the anterior arch develops from extensions of the lateral ossification centres without a separate anterior centre.

SECOND CERVICAL VERTEBRA

– The second cervical vertebra (C2) is called the axis because its odontoid process acts as a pivot around which the atlas and head rotate.

Features

·  The axis is distinguished by the presence of a dens (odontoid process) projecting upward from its body.

·  It consists of the following parts:

• Body
• Odontoid process (dens)
• Vertebral arch
• Superior and inferior articular processes
• Transverse processes
• Spinous process

Body

• Superior surface: It is continuous with the base of the dens.
• Inferior surface: Its anterior margin projects downward over the intervertebral disc.
• Anterior surface: It presents a vertical median ridge with a shallow depression on either side.

Attachments

• The longus colli muscle is inserted into the anterior surface of the body.
• The anterior longitudinal ligament is attached to the anterior surface of the body.

Odontoid process (dens)

• The dens is a strong, tooth-shaped bony projection, approximately 13 mm long, extending upward from the body of the axis.
• It represents the centrum of the atlas, which becomes incorporated into the axis during development.
• It serves as a pivot around which the atlas and skull rotate during side-to-side movements of the head.

Features

• Base: It is the broad lower part that joins the body of the axis.
• Apex: It forms the narrow, conical upper end of the dens.
• Anterior articular facet: It is a smooth facet on the anterior surface of the dens that articulates with the posterior surface of the anterior arch of the atlas.
• Posterior surface: It bears a shallow groove for the transverse ligament of the atlas.

Attachments

• Apex: It provides attachment to the apical ligament of the dens.
• Lateral surfaces: They provide attachment to the right and left alar ligaments.

Developmental Significance

– The apical ligament of the dens is traditionally described as a remnant associated with the notochord.

Vertebral arch

– The vertebral arch consists of two pedicles and two laminae and supports the articular and transverse processes and the spinous process.

Pedicles

• The pedicles are short and strong, with their superior parts largely occupied by the superior articular facets.
• Superior vertebral notches: They are shallow and lie behind the superior articular facets.
• Inferior vertebral notches: They are relatively deep.

Laminae

• The laminae are broad, thick, and strong. They unite posteriorly to form the prominent spinous process.
• Attachments: The laminae provide attachment to the ligamenta flava, which connect them to the laminae of the third cervical vertebra.

Articular Facets

Superior Articular Facets

• Each superior articular facet is large, oval, and situated lateral to the dens. It lies on the upper surface of the axis near the junction of the body and vertebral arch. It articulates with the inferior articular facet of the corresponding lateral mass of the atlas to form the lateral atlanto-axial joint.

Inferior Articular Facets

• The inferior articular facets are situated behind the transverse processes. They articulate with the superior articular facets of the third cervical vertebra (C3).

Transverse Processes

• The transverse processes are short and terminate in a single tubercle, which represents the posterior tubercle. Each transverse process contains a foramen transversarium directed upward and laterally.

Attachments

• Tip of transverse process: It provides attachment to the following muscles:
  • Levator scapulae (origin)
  • Scalenus medius (origin)
  • Splenius cervicis (insertion)
• Superior and inferior surfaces: They provide attachment to the intertransversarii muscles.

Spinous Process

• The spinous process is large, thick, and bifid. Its inferior surface presents a deep groove.
• It provides attachment to several muscles and ligaments that support and move the head and neck.

Attachments

Inferior surface and groove

– The following structures are attached to the inferior aspect and adjoining parts of the spinous process:

• Ligamentum nuchae
• Semispinalis cervicis
• Spinalis cervicis
• Multifidus
• Interspinales cervicis

Lateral surfaces

– The obliquus capitis inferior muscle arises from the lateral surface of the spinous process.

Posterior aspect

– The rectus capitis posterior major muscle arises from the spinous process of the axis.

SEVENTH CERVICAL VERTEBRA

– The seventh cervical vertebra (C7) is called vertebra prominens because of its long, prominent spinous process, which projects almost horizontally backward.

Features

Spinous Process

• The spinous process is long, thick, and nearly horizontal, with a rounded tip.
• Unlike typical cervical vertebrae, its spinous process is not bifid.
• The tip can be palpated beneath the skin at the lower end of the nuchal furrow, making it an important surface landmark.

Attachments

– The spinous process provides attachment to the following structures:

• Ligamentum nuchae
• Trapezius
• Rhomboid minor
• Serratus posterior superior
• Deep muscles of the neck

Transverse Processes

• The transverse processes are relatively large and project laterally.
• The posterior tubercle is prominent, whereas the anterior tubercle is small or may be absent.
• The posterior tubercle provides attachment to the suprapleural membrane (Sibson’s fascia).

Foramen Transversarium

• The foramen transversarium is small and may occasionally be duplicated or absent.
• Unlike the upper cervical vertebrae, it does not normally transmit the vertebral artery.
• It usually transmits an accessory vertebral vein, while the main vertebral vein may also pass through this foramen.

HYOID BONE

• Hyoid bone is a U-shaped arch with convexity directed upward and forward (hyoid = U-shaped in Greek).

Development

• Upper part of the body and lesser cornua of hyoid bone develop from the 2nd pharyngeal arch cartilage (Reichert’s cartilage).Viva MCQ

• Lower part of the body and greater cornua of the hyoid bone develop from the 3rd pharyngeal arch cartilage.Viva, MCQ

Parts of Hyoid Bone

• The hyoid bone consists of the following parts (Figs 3.12, 3.13, Flowchart 3.4):

1. Body

2. Pair of greater cornua

3. Pair of lesser cornua

Body of hyoid bone

• It is elongated, quadrilateral, and flat arch of bone.

• It has two surfaces (anterior and posterior), two lateral ends, and two borders (superior and inferior).

• Anterior surface: It is convex.

• Posterior surface: It is concave and directed downward and backward.

• Lateral end of the body is continuous with the greater cornua.

Greater cornua

• These are flattened bars. They extend backward from the lateral end of the body. Each greater cornua has two surfaces (upper and lower), two

border (medial and lateral), and tubercle at the posterior end.

Lesser cornua

• They are small conical parts of bone that project upward from the junction of the body and greater cornua.

Attachments (Fig. 3.14)

Body

1. Geniohyoid and mylohyoid insert on the anterior surface of the body, whereas hyoglossus originates.

2. Genioglossus is inserted and thyrohyoid membrane is attached to the upper border of the body.

3. Pretracheal fascia is attached to the lower border of the body. Sternohyoid and superior belly of omohyoid are inserted on the lower border of the body.

Greater cornua

1. Hyoglossus and middle constrictor of pharynx originates at the medial end of greater cornua.

2. Thyrohyoid membrane and stylohyoid (insertion) are attached at the medial border of greater cornua.

3. Thyrohyoid muscle inserts on the lateral border of greater cornua.

Lesser cornua

• It provides attachment to the stylohyoid ligament at its tip and middle constrictor of pharynx from its posterolateral aspects.

Ossification

• Chondrification of hyoid bone begins in 5th week of IUL and completes by 3rd to 4th months.

• Hyoid bone ossifies from 6 centers as follows:

– Two for body

– One for each of the greater and lesser cornua

• Ossification of body and greater cornua begins at around birth. Lesser cornua ossifies around puberty. Greater cornua fuses with the body in 3rd decade and lesser cornua in 4th decade.