Functional Anatomy of the Cervical Spine

Introduction

The cervical spine supports and promotes movement of the head and neck. Intervertebral discs maintain the spaces between the vertebrae. These discs act like shock absorbers throughout the spinal column to cushion the bones as the body moves. Ligaments hold the vertebrae in place, and tendons attach the muscles to the spinal column. The cervical spine is subjected to extrinsic factors such as repetitive movements, whole body vibrations and static load.

Key Terms

Axes: lines around which an object rotates. The rotation axis is a line that passes through the centre of mass. There are three axes of rotation: sagittal passing from posterior to anterior, frontal passing from left to right, and vertical passing from inferior to superior. The rotation axes of the foot joints are perpendicular to the cardinal planes. Therefore, motion at these joints results in rotations within three planes. Example: supination involves inversion, internal rotation, and plantarflexion.

Bursae: reduce friction between the moving parts of the body joints. A bursa is a fluid-filled sac. There are four types of bursae: adventitious, subcutaneous, synovial, and sub-muscular.

Capsule: one of the characteristics of the synovial joints. It is a fibrous connective tissue which forms a band that seals the joint space, provides passive and active stability and may even form articular surfaces for the joint. The capsular pattern is "the proportional motion restriction in range of motion during passive exercises due to tightness of the joint capsule."

Closed pack position: the position with the most congruency of the joint surfaces. In this position, joint stability increases. For example, the closed pack position for the interphalangeal joints is a full extension.

Degrees of freedom: the direction of joint movement or rotation; there is a maximum of six degrees of freedom, including three translations and three rotations.

Ligament: fibrous connective tissue that holds the bones together.

Open (loose) pack position: position with the least joint congruency where joint stability is reduced.

Planes of movement: describe how the body moves. Up and down movements (flexion/extension) occur in the sagittal plane. Sideway movements (abduction/adduction) occur in the frontal plane. The transverse plane movements are rotational (internal and external rotation).

Cervical Spine Structure

Cervical Vertebrae

There are seven lumbar vertebrae, which are known as C1-C7 whose role is to support and promote movement of the head. Considering the small weight-bearing load of the cervical spine, these vertebral bodies do not require height, just flexibility to facilitate movement. With increased range of motion in the cervical spine, there is heightened injury potential to the spinal cord and its associated neurovascular structures.

The seven vertebral bodies have unique characteristics:

Atlas

• no vertebral body
• no spinous process

Axis

• odontoid process (dens) extending superiorly from anterior portion of the vertebra

C3-C6

• triangular vertebral foramen
• bifed spinous process
• transverse foramina (space for nerves and vasculature)

C7

• singular spinous process
• larger spinous process

**In supine: It may be difficult to palpate the spinous process of C3-C6 with normal cervical lordosis

Intervertebral Disc (IVD)

Overall, intervertebral discs involve 25% of the height of the entire spine. In the cervical region, the discs compromise 40% of the height. This increased height compared to vertebral body height provides an advantage for mobility. The nucleus pulposus of cervical discs dries out by the age of 30 to a firm, fibrocartilaginous plate.

The following are characteristics of the cervical spine intervertebral discs:

• thicker anteriorly than posterior
• concave superior surface
• convex inferior surface
• movement limited by uncinate process
• anteroposterior translation does occur

** Due to location of uncinate process, posterolateral disk herniations are less frequent

Cervical Lordosis

The cervical spine has a normal lordotic posture. Biomechanically, this posture is able to resist large compressive loads and decrease stress on vertebral end plates. Compressive load distribution in the cervical spine takes place 36% by the anterior column and 64% by the posterior facet joints

Kinematics and Joints of the Cervical Spine

Kinematics

The most mobile part of the vertebral column is the cervical spine. Normal range of motion for flexion is around 40 degrees and extension 50 degrees. The largest contributor to flexion/extension is from segments C4C5 and C5C6 in sitting and C6C7 in supine. The segment with the least contribution to flexion/extension is C7T1. Lateral flexion normal range of motion is close to 30 degrees. The segment that allows for most movement in this plane is C3–C4 and C6–C7 segments. Lastly, cervical rotation has the highest range of motion normal values close to 70 degrees. Flexibility in this plane is mainly achieved through C1C2 segment.

Joints of Cervical Spine

Joint	Disc Joint	Facet Joint or Zygapophyseal Joints	Uncovertebral Joint	Atlanto-Axial Joint	Atlanto-Occipital Joint
Location/articulations	between vertebral bodies	formed by articulations of superior and inferior articular processes from adjacent vertebrae	between 5 lower cervical vertebral bodies anteromedially to nerve root posteromedially to vertebral artery	between atlas an axis 2 lateral: interior facetws of lateral masses of C1 and superior facets of C2 1 medial: between dens C2 and articular facet C1	between spine and cranium between superior facets of lateral masses of the atlas and the occipital condyles
Functions	bear weight facilitate motion absorb shock	guide motion at the segmental level determine direction of motion	control movement limit lateral flexion	allow cervical rotation	flexion and extension of the head on the neck lateral flexion
Orientation/Composition		upper c-spine- horizontal lower-more vertical		median: pivot-type synovial joint lateral: plane -type synovial joint	condyloid-type synovial joint

Spinal Ligaments

Ligaments Unique to Cervical Spine

Ligament	Origin	Insertion	Role/Function
Nuchal ligament	occiput	tips of the spinous process from C1-C7	limit hyperflexion
Transverse ligament		connects lateral masses of atlas	anchors dens in place
Apical ligament	dens of the axis	foramen magnum	stabilises skull on spiine
Lar Ligament	dens of the axis	occiput	limits atlanto-axial rotation
Cruciform or Cruciate Ligament 1. superior longitudinal band 2. inferior longitudinal band 3. transverse band	superior: transverse band inferior: transverse band transverse: dens of axis	superior: foramen magnum second vertebral body transverse ligament: between lateral masses of atlas	hold dens in place

Muscles of the Cervical Spine

Muscles of the cervical spine can be divided by location or by the movement they create.

Anterior (Prevertebral) Vertebral Muscles

These are also termed Deep cervical flexor:

• Rectus Capitis Anterior
• Rectus Capitis Lateralis
• Longus capitis
• Longus colli/ Longus cervicis (3 portions: superior oblique, inferior oblique, vertical)

Lateral Vertebral Muscles (Paravertebral)

Scalenes - anterior, middle, posterior and minimus scalene muscles

Posterior Vertebral Muscles

These can be further divided into intrinsic and extrinsic muscles.

Extrinsic muscles

Trapezius and Levator scapulae

Intrinsic muscles

• Superficial muscles :
  • splenius capitis
  • splenius cervicis
• Deep muscles:
  • Suboccipital group -
    • rectus capitis posterior major
    • rectus capitis posterior minor
    • obliquus capitis inferior
    • obliquus capitis superior
  • Transversospinalis muscles -
    • semispinalis capitis
    • semispinalis cervicis
    • rotatores cervicis
    • multifidus (these are also known as deep neck extensors)
  • Interspinales and intertransversarii

Movement	Muscles
Flexion	Longus colli Sternocleidomastoid Scalene anterior Longus capitis Rectus capitis anterior (head only)
Extension	Levator Scapulae Splenius cervicis Splenius capitis Trapezius Erector spinae Rectus capitis posterior, major and minor (head only)
Lateral flexion	Scalene anterior, medius and posterior Sternocleidomastoid Splenius capitis Trapezius Erector spinae Rectus capitis lateralis (head only)
Rotation	Semispinalis cervicis Multifidus Scalene anterior Splenius cervicis and capitis Sternocleidomastoid Inferior oblique (head only) Rectus captitis posterior major (head only)

Cervical Spine Flexors

Muscle	Origin	Insertion	Innervation	Action
rectus capitis anterior	atlas	occiput		flexion
longus colli	transverse processes of C3 to C5 and the vertebral bodies of C5 to T3	anterior tubercle of C1, the vertebral bodies of C2 to 4, and the transverse processes of C5 and C6.		flexion
longus capitis	transverse processes of C3 to C6	occipital bone		flexion
anterior scalene	transverse processes of C3 to C6	first rib		flexion, respiration
sternocleidomastoid	manubrium and the medial portion of the clavicle	mastoid process of the temporal bone
paravertebral cervical muscles (rectus capitis anterior, longus colli. longus capitis, rectus capitis lateralis)

Cervical Spine Extensors

Muscle	Origin	Insertion	Innervation	Action
obliques capitis superior	transverse process of the atlas	occipital bone		stabilises atlanto-occipital joint
oblique capitis inferior	spinous process of the axis and inserts into the transverse process of the atlas,	tansverse process of atlas		stabilises atlanto-occipital joint
rectus capitis posterior major	spinous process of C2	occipital bone
rectus capitis posterior minor	posterior tubercle of the atlas	occipital bone
rotatores cervicis	inconsistent and blend with other muscles			aid in stabilisation of spinal column
multifidus	articular processes of C4 to C7	spinous processes		aid in stabilisation of spinal column
semispinalis cervicis	transverse processes of T1 to T5 and inserts into the spinous processes of C2 to C5.	spinous processes of C2 to C5.
semispinalis capitis	transverse processes T1 to T7 and articular process of C4-C7	occipital bone
spinalis capitis	spinous processes of C7 and T1	occipital bone
longissiumus capitis	transverse process of T1-T5 and articular process of C4-C7	mastoid process of temporal bone
longissium cervis	transverse process of T1-T5	transverse processes of C2-C6
iliocostal cervicis	ribs 3-6	transverse process of C4-C6
spelnius cervicis	spinous process T3-T6	transverse process of C1C3
splenius capitis	spinous process C7-T3 and nuchal ligament	occipital bone
trapezius	occipital bone, nuchal ligament and spinous process C7-T12	lateral third of clavicle, the acromian and the spine of s scapula

Lumbar Spine Lateral Flexors

Muscle	Origin	Insertion	Innervation	Action
rectus capitis lateralis	transverse process of the atlas	suboccipital bone		stabilising atlanto-occipital joint
obliquus capitis
multifidus
longissimus cervcis
splenius cervicis
splenius capitis
iliocostalis cervicis
posterior scalene	transverse processes of C4 to C6	second rib		aid in respiration
middle scalene	transverse processes C1-C7	first rib		aid in respiration
anterior scalene				aid in respiration
levator scapula	transverse process C1-C4	medial border of scapula
sternocleidomastoid
trapezius

Lumbar Spine Rotators

Muscle	Origin	Insertion	Innervation	Action
obliques capitis inferior				ipsilateral rotation of atlanto-axial joint
rectus capitis posterior				ipsilateral rotation of the head on the neck
multifidus				contralateral neck rotation
semispinalis capitis				contralateral neck rotation
spinalis capitas				ipsilateral neck rotation
longissimus capitis				ipsilateral neck rotation
sternocleidomastoid				contralateral neck rotation

Innervation of the Cervical Spine

Nerves originating from the cervical plexus innervate the muscles of the neck. Each nerve root in the cervical spine exits above its corresponding nerve root. There are eight pairs of cervical nerves despite the presence of seven cervical vertebrae. C8 nerve root exits below the seventh cervical vertebrae. The accessory nerve which is cranial nerve X1 innervates the sternocleidomastoid as well as the trapezius.

Nerve	Motor	Sensory
C1	head and neck extensor; rectus capitus anterior and lateral longus capitus
C2	head and neck extensor; rectus capitus anterior and lateral, longus capitus, longus colli	lateral occiput and submandibular area
C3	head and neck extensors, longus capitus, longus colli, levator scapulae, scaleni, and trapezius	lateral occiput and lateral neck, overlapping C2
c4	head and neck extensors, longus coli, levator scapulae, scaleni, trapezius, and diaphragm.	lower lateral neck and medial shoulder area
C5	deltoid, biceps, bicep tendon reflex	clavicle level and lateral arm
C6	biceps, wrist extensors, brachioradialis tendon reflex	lateral forearm, thumb, index and half of 2nd finger
C7	wrist flexors, triceps, triceps tendon reflex	second finger
C8	finger flexors, interossei	medial forearm, ring and little finger
T1	interossei	medial arm

Vascular Supply of the Cervical Spine

Vertebral arteries, veins and nerves pass through the transverse foramina of the cervical vertebrae. C7 is the only exception in that the vertebral artery passes around the vertebra instead of through the transverse foramen.The neural components sit posterior to the vertebral artery.

The cervical spine vascular supply is primarily provided by the vertebral arteries one on each side. These arteries arise from the subclavian arteries that originate directly from the arch of the aorta on the right side, and via the brachiocephalic trunk on the left side.

** The common carotid arteries bifurcates into the internal and external carotid arteries at the C3 segmental level. Only the external carotid artery provides any blood supply to the neck.

Clinical Relevance

A disc herniation is a condition where the nucleus pulposus, which is the gel-like centre of the disc, protrudes through the annulus fibrosis, which is the surrounding ring of collagen fibres. While disc herniations in the cervical spine are a lot less common than in the lumbar spine, it can still occur. Typically, it occurs at the level of C5 to 6 and C6 to 7.

Conditions like rheumatoid arthritis can affect the stability of the atlanto-axial joint, which can result in serious neurological consequences due to the proximity of the spinal cord. Laxity in the transverse ligament is also present in 14% to 22% of individuals with Down syndrome. sternocleidomastoid is wry neck, or torticollis, where the head appears to be tilted at an odd angle.

prevertebral cervical muscles, that can be thought of as the equivalent of the core of the neck and play an important role in the stabilisation of the neck. Dysfunction in these muscles can play a part in cervicogenic pain. Let's look at the flexion movement again.

Trigger points that develop in the suboccipital muscles can refer pain to the head causing headaches.

(daphne)

1. Disc herniations are a common low back condition. They occur when the nucleus pulposus displaces from the intervertebral space. According to Yoon et al., when there is imaging confirmation of lumbar disc herniation that is "consistent with clinical findings, and failure to improve after six weeks of conservative care", surgical intervention may be required. You can read more about the management of disc herniation symptoms here.
2. Spinal stenosis is a narrowing of the spinal canal. Spinal stenosis can be caused by a range of conditions, such as tumours or bone spurs. You can learn about low back pain assessment and prognosis by taking this course.
3. Diastasis recti is a very common condition where the linea alba stretches and produces a gap between the two sides of the rectus abdominis muscle. Learn more about diastasis recti here.