The cervical portion of the spine is an important one anatomically and clinically. It is within this region that the nerves to the arms arise via the brachial plexus, and where the cervical plexus forms providing innervation to the diaphragm among other structures. The cervical spine also allows passage of important vasculature to reach the brain and provides attachment sites for muscles that move the head, neck, and shoulder girdle.
To understand this intricate region, we will consider the bony structures first, and then discuss the ligaments, nerves, and musculature that are associated with this region of the spinal column, concluding with some clinical implications of damage to some of these structures.
|Types of Vertebrae||Typical (C3-C6), atypical (C1, C2, C7)|
|Structure of Typical Vertebrae||Vertebral body, transverse process, spinous process, vertebral foramen, vertebral arch, articular processes|
|Intervertebral Discs||Consisting of an inner component called the nucleus pulposus surrounded by the annulus fibrosus, they allow the vertebrae to move and act as shock absorbers.|
Continuations from thoracic spine: anterior longitudinal ligament, posterior longitudinal ligament, ligamentum flavum, intertransverse ligament, interspinous ligament, nuchal ligament
Unique ligaments: alar ligaments, apical ligament, transverse ligament
|Nerves||Cervical plexus and brachial plexus|
Anterior neck muscles: rectus capitis anterior and lateralis muscles, longus capitis and colli muscles, anterior, middle and posterior scalene muscles
Superficial back muscles: trapezius, levator scapulae, rhomboid minor, serratus posterior superior
Suboccipital muscles: rectus capitis posterior major and minor muscles, obliquus capitis superior and inferior muscles
Spinotransversales muscles: splenius capitis and cervicis muscles
Erector spinae muscles: iliocostalis cervicis and thoracis muscles, longissimus capitis and cervicis muscles, spinalis cervicis muscle
Transversospinalis muscles: semispinalis capitis, cervicis, and thoracis muscles, multifidus, rotatores cervicis muscle
|Injuries||Disc herniation, spinal stenosis, atlantoaxial subluxation, fractures|
- Cervical Spine Vertebrae
- Intervertebral Discs
- Cervical Spine Ligaments
- Nerves Arising from the Cervical Spine
- Muscles Attaching to the Cervical Spine
- Anterior neck muscles (flex head, flex neck, elevate ribs 1 and 2)
- Superficial back muscles (extend head and neck, elevate and retract scapula, elevate ribs)
- Suboccipital muscles (extend and rotate head)
- Deep back muscles: spinotransversales muscles (extend neck, rotate the head)
- Deep back muscles: erector spinae muscles (extend the neck and head)
- Deep back muscles: transversospinalis muscles (extend the neck, extend and rotate the head)
- Injuries of the Cervical Spine
- Related diagrams and images
Cervical Spine Vertebrae
The bony component of the cervical spine is made up of seven vertebrae. The lower five are more similar to each other than the upper two (Atlas – C1, Axis – C2).
Typical Cervical Vertebrae: C3-C6
The lower five cervical vertebrae are made up of the following structures:
- Vertebral body: Is small compared to the vertebral bodies in the rest of the spinal column owing to the fact they bear less weight than vertebrae further down the spine. Laterally, the vertebral bodies project slightly upwards creating the uncinate processes. These processes articulate with the bodies of the vertebra superior to them producing uncovertebral joints.
- Transverse processes (TVP): A typical feature of most vertebrae in the spinal column; these project laterally with one on each side. In the cervical spine, the transverse processes are unique due to the presence of the foramen transversarium or transverse foramen. Within these foramen, or holes, of C1-C6, run one of the two major arterial supplies to the brain, the vertebral arteries, the other being the internal carotid arteries. Accompanying the arteries are the vertebral veins. Additionally, the transverse processes of the vertebrae in the cervical spine are grooved for passage of spinal nerves. This groove divides the transverse process such that most laterally, each process has an anterior and posterior tubercle, for the attachment of muscles.
- Spinous process (SP): Project posteriorly and may be palpated in some cases since they lie beneath the skin on the back. The spinous processes of C3-C5 tend to be short and bifid, meaning that they divide into two parts posteriorly, with the spinous process of C6 being slightly longer but still bifid.
- Vertebral foramen: Is the bony canal in which the spinal cord runs. It is triangular in shape and comparatively large to accommodate the expansion of the cervical component of the spinal cord that provides all innervation to the upper limb. A similar enlargement is seen in the lumbar spinal cord to accommodate innervation of the lower limb. The vertebral foramen is made up of the posterior aspect of the vertebral body and the vertebral arch.
- Vertebral arch: Refers to the posterolateral bony components of the vertebral foramen. Extending posteriorly from each side of the vertebral body is a pedicle that runs between the body and the transverse process. The two lamina (one on each side) extend from the transverse processes to meet posteriorly at the spinous process.
- Articular processes (4): These are located immediately posterior to the transverse process and its foramen transversarium. There are two superior and two inferior processes. Each process has a smooth surface known as an articular facet. The two superior facets will articulate with the two inferior facets of the vertebra above, creating the zygapophyseal (or facet) joints. They may be referred to as joints of the vertebral arch since the processes themselves form on the lateral bony components of the arch. When the vertebrae are stacked one on top of the other, the vertebral arch, articular processes, and zygapophyseal joints of adjacent vertebrae create a passageway for spinal nerves known as the intervertebral foramen. The intervertebral foramen allows the spinal nerves at each vertebral level to exit the vertebral canal. Finally, the almost horizontal orientation of the articular facets in the cervical spine is, in part, responsible for giving the cervical spine the greatest variety and range of movement.
Atypical Cervical Vertebrae: The Atlas (C1) and Axis (C2), and C7
Unlike other vertebrae, the atlas does not have a spinous process or a body. When seen from above, the atlas is really a ring shape that thickens laterally to produce the lateral masses, which are joined by anterior and posterior arches. The anterior arch has three features to note:
- an anterior tubercle on the anterior surface
- a facet for the dens of the axis on the posterior surface
- and on either side of the facet, a tubercle for the transverse ligament that holds the dens in place
The posterior arch, instead of a spinous process, has a posterior protrusion known as the posterior tubercle. In addition, grooves for the vertebral arteries lay just posterior to the superior articular facets located on the lateral masses.
On the superior and inferior surfaces of the lateral masses are facets for articulations with other bones. Superiorly, the facets articulate with the occipital condyles of the occipital bone of the skull, and form the atlanto-occipital joints. Inferiorly, the facets articulate with the axis, forming the lateral atlanto-axial joints. Protruding laterally from the lateral masses are the transverse processes of the atlas that again feature the foramen transversarium.
The axis is more similar to the rest of the cervical spine vertebrae than the atlas but it does have an incredibly unique feature; the dens, or odontoid process. Often characterized as tooth-like or peg-like, this process is larger and longer than most other anatomical processes and extends from the body of C2. The dens and the spinal cord are encircled by the atlas. The dens makes an articulation with the posterior surface of the anterior arch of the atlas (the median atlantoaxial joint) and is held in place by the transverse ligament. The dens, and its articulation with the atlas, acts as a pivot around which rotation of the head can occur. The transverse ligament runs posterior to the dens (and anterior to the spinal cord), forming the posterior wall of the joint
On the posterior aspect of the dens are two facets for attachment of the alar ligaments. These ligaments connect the dens to the medial aspect of each occipital condyle and help restrict excessive rotation of the head.
Note: the atlanto-occipital joints allow for nodding, flexion/extension, or ‘yes’ motions of the head. The articulations between the atlas and axis (the two lateral atlantoaxial joints and the median atlantoaxial joint between the dens and the atlas) allow for rotation of the head or ‘no’ motions.
C7 Is atypical for three reasons. The first is that the spinous process of C7 is the longest and can be easily palpated when the head is flexed forward as it is quite prominent in this position. In addition, the spinous process is not bifid. Finally, the foramen transversarium is quite small compared to the size of the transverse process and does not contain the vertebral arteries, just vertebral veins.
Although not technically a bony component, the intervertebral discs lie in between all cervical vertebrae with the exception of C1 and C2. These discs can be quite significant clinically as they make up the inferior half of the anterior border of the intervertebral and vertebral foramina. They are also considered to create symphysis joints (a type of cartilaginous joint) with the vertebrae superior and inferior to each disc, providing the spinal column with rigidity. The discs allow movement between vertebrae, but also function as shock absorbers, providing a cushion between the vertebrae during weight-bearing activities. The outer component of the disc is known as the annulus fibrosus. It is made of fibrocartilage, and functions to contain the inner segment of the disc: the nucleus pulposus.
Note: The strong and fibrous annulus fibrosus is thinner posteriorly (i.e. where it makes up part of the anterior portion of the intervertebral and vertebral foramina), and may actually be incomplete in the cervical region of adults. Under these conditions, the more semifluid nucleus pulposus can be pushed posteriorly, especially when the neck is flexed as this places pressure on the disc anteriorly. This can cause the nucleus pulposus to bulge posteriorly (a herniated disc) and impinge on a spinal nerve, causing pain.
Cervical Spine Ligaments
The cervical spine ligaments are a combination of ligaments that continue from lower regions of the vertebral column (that change names as they reach C2) and ligaments that are unique to the cervical spine.
Ligaments that continue from below C7 (from anterior to posterior)
- Anterior longitudinal ligament (ALL): Attaches to and covers the anterior and lateral aspects of the vertebral bodies and intervertebral discs. This ligament extends from the anterior surface of the sacrum to C2. From C2 to C1 it is known as the anterior atlantoaxial membrane, and from C1 to the anterior aspect of the foramen magnum as the anterior axial-occipital membrane. These are the only spinal ligaments that limit hyperextension of the vertebral column.
- Posterior longitudinal ligament (PLL): Is a much narrower ligament that runs along the posterior aspect of the vertebral bodies, or alternatively, along the anterior aspect of the vertebral canal (the canal is made up of all of the vertebral foramen stacked on top of one another). It extends from the sacrum to C2. From C2, the PLL strengthens and becomes known as the tectorial membrane. It then passes through the foramen magnum to attach to the floor of the cranial cavity. Functionally, it weakly resists hyperflexion of the vertebral column, and helps prevent posterior herniations of the nucleus pulposus. Note: The PLL does not help prevent posterolateral herniations as it is absent in this region.
- Ligamentum flavum (pl. flava): Runs between the lamina of adjacent vertebrae. Because of its location, along with limiting hyperflexion, these ligamentous sections help enclose the posterior aspect of the vertebral canal. They also assist in straightening the spinal column after flexion. As with the ALL, the ligamentum flava continues from C2 and C1 as the posterior atlanto-axial and atlanto-occipital membranes. These membranes limit excessive motion at the atlanto-occipital joints.
- Intertransverse ligament: Runs between the transverse processes of adjacent vertebrae.
- Interspinous ligament: Is a weak ligament that runs between the spinous processes of adjacent vertebrae.
- Nuchal ligament: Is a continuation of the supraspinous ligament in the cervical spine (C7 and above). Like the supraspinous ligament in the rest of the vertebral column, it runs along the tips of the spinous processes and is quite strong. It differs however in the cervical region, by extending posteriorly away from the spinous processes. This accommodates for muscular attachment, along with resisting hyperflexion.
Ligaments unique to the cervical spine
- Alar ligament: Runs from the posterior aspect of the dens of C2 to the lateral margins of the foramen magnum.
- Apical ligament: Connects the tip or apex of the dens of C2 to the anterior aspect of the foramen magnum.
- Transverse ligament: Holds the dens against the posterior aspect of the anterior arch of C1. Arising from this ligament are superior and inferior longitudinal ligamentous bands that attach the dens to the occipital bone and to the body of C2. In combination, the transverse ligament and the bands are known as the cruciate ligament.
Nerves Arising from the Cervical Spine
Arises from the anterior rami of the spinal nerves associated with C1-C4 (some texts include the C5 nerve root). This plexus lies deep to the sternocleidomastoid (SCM) muscle and anteromedial to the levator scapulae and middle scalene muscles. The branches of the cervical plexus can be categorized as either muscular or cutaneous.
- Phrenic nerve (C3-5): supplies the diaphragm.
- Ansa cervicalis (C1-3): supplies the infrahyoid muscles.
- Suboccipital Nerve (C1): supplies the suboccipital muscles.
- Nerves roots of C1-C3: supply prevertebral muscles.
The cervical plexus also contributes branches to these nerves:
- Dorsal scapular (C4,5): supplies the rhomboid major and minor, and levator scapulae muscles.
- Long thoracic (C5-7): supplies the serratus anterior muscle.
It arises from the anterior rami of the spinal nerves associated with C5-T1 where the nerve roots appear between the anterior and middle scalene muscles. The nerve roots quickly combine to form nerve trunks: nerve roots C5 and C6 form the upper trunk, C7 the middle trunk, and C8 and T1 the lower trunk. Each trunk divides into an anterior and posterior division, which then combine to form three cords, the lateral, medial, and posterior cords. The cords then combine to form the five major nerves that supply the majority of the upper limb.
- Musculocutaneous (C5-7): Supplies muscles of the anterior compartment of the arm, and the skin of lateral forearm.
- Median (C5-8, T1): Supplies the majority of the muscles in the anterior compartment of the forearm, and the skin of the lateral 3 and a half fingers (mostly palmar aspect) and palm.
- Ulnar (C8, T1): Supplies the majority of the intrinsic muscles of the hand, and the skin of the medial 1 and a half fingers and hand (palmar and dorsal aspects).
- Radial (C5-8, T1): Supplies all muscles in the posterior compartments of the arm and forearm, and the skin of lateral 3 and a half fingers (dorsal aspect).
- Axillary (C5,6): Supplies the deltoid and teres minor muscles, and the skin over the deltoid.
Also arising from the brachial plexus are a number of minor nerves. In addition to the dorsal scapular and long thoracic nerves mentioned previously, these minor nerves are the:
- Nerve to subclavius (C5,6): Supplies the subclavius muscle.
- Suprascapular (C5,6): Supplies two of the rotator cuff muscles (the supraspinatus and infraspinatus).
- Lateral pectoral (C5-7): Supplies the pectoralis major muscle.
- Medial pectoral (C8, T1): Supplies the pectoralis major and pectoralis minor muscles.
- Medial cutaneous nerves of the arm and forearm (C8, T1): Skin of the medial aspect of the arm and forearm.
- Thoracodorsal (C6-8): Supplies the latissimus dorsi muscle.
- Upper and lower subscapular (C5,6): Together they supply one of the rotator cuff muscles, the subscapularis muscle. The lower subscapular nerve alone supplies the teres major and teres minor muscles.
Muscles Attaching to the Cervical Spine
There are many muscles in the cervical region, not all of them attach to the cervical spine, but many of them do. The following are muscles that either originate or insert (at least partially), or both, onto the vertebrae in the cervical spine. If a muscle attaches to the skull it will move the head, if it does not, the muscle will only move the neck.
Anterior neck muscles (flex head, flex neck, elevate ribs 1 and 2)
- Rectus capitis anterior: Origin - TVP of C1.
- Rectus capitis lateralis: Origin - TVP of C1.
- Longus capitis: Origin - anterior tubercles of TVPs of C3-C6.
- Longus colli: Part of origin - bodies of C5-C7, TVPs of C3-C, Insertion - anterior tubercle of TVP of C1, bodies of C1-C3, TVPs of C3-C6.
- Anterior scalene: Origin - anterior tubercles of TVPs of C3-C6.
- Middle scalene: Origin - TVPs of C2-C7.
- Posterior scalene: Origin - posterior tubercles of TVPs of C4-C6.
Superficial back muscles (extend head and neck, elevate and retract scapula, elevate ribs)
Suboccipital muscles (extend and rotate head)
Deep back muscles: spinotransversales muscles (extend neck, rotate the head)
Deep back muscles: erector spinae muscles (extend the neck and head)
Deep back muscles: transversospinalis muscles (extend the neck, extend and rotate the head)
- Semispinalis capitis: Origin – TVP of C7, articular processes of C4-6.
- Semispinalis cervicis: Origin - articular processes of C4-C6, Insertion - SP of C2-C5.
- Semispinalis thoracis: Part of Insertion - SPs of C6 and C7.
- Multifidus: Part of Insertion - SPs of all cervical vertebrae.
- Rotatores cervicis: Part of Insertion - SPs of all cervical vertebrae.
Injuries of the Cervical Spine
Damage to the cervical portion of the spinal cord can be catastrophic, resulting in various degrees of disability (i.e. quadriplegia and difficulty breathing) or even death. Protection of the spinal cord and spinal nerves falls to the vertebral column and its associated ligaments and muscles. Dysfunction or injury of these components could lead to pain and/or weakness due to obtrusion of structures into the intervertebral or vertebral foramina.
Disc Herniation and Spinal Stenosis
Typically associated with pain in the low back, disc herniation occurs almost as often in the cervical region. Tears or weakness in the posterolateral aspect of the intervertebral disc can cause the nucleus pulposus to be squeeze out and impinge on either the spinal cord or adjacent spinal nerve(s).
Degeneration and hypertrophy in the ligamentum flavum and the zygapophyseal joints, in addition to a mild disc protrusion, can cause a syndrome known as spinal stenosis, or narrowing of the vertebral canal. Symptoms depend on the spinal level at which the disc herniation or stenosis occurs. For example, a disc herniation between C5 and C6 in the cervical region, would cause pain in the neck, shoulder, arm, and hand. However, a disc herniation higher up, between C2 and C3, may affect the phrenic nerve and cause problems with breathing.
Change in the tautness of the transverse ligament means that the dens is not held as tightly against the anterior arch of the atlas or C1, resulting in a condition known as atlantoaxial subluxation. The transverse ligament lies between the dens and the spinal cord, therefore, any increase in motion of the dens can result in compression of the spinal cord. Conditions in which there is a softening of connective tissue structures, as in 20% of people with Down syndrome, can exhibit laxity or a complete lack of the transverse ligament.
This misalignment can also occur as a result of a major trauma or some types of arthritis. For example, in rheumatoid arthritis, the immune system erroneously attacks tissues associated with synovial joints, including surrounding ligaments, leading to tissue inflammation and destruction. This disease typically starts in the joints of the extremities, but after ten years, 80% of patients will have involvement of the cervical spine. Symptoms in these cases can include:
- mild neck pain
- progressing to weakness
- bowel and bladder dysfunction
- trouble with walking or arm movements
Laxity in cervical spine ligaments causing atlantoaxial subluxation and compression of the spinal cord cannot be viewed with x-ray. The best way to view the extent of the subluxation and spinal compression in cases of rheumatoid arthritis is through MRI.
Fractures of the Cervical Spine
Are the most common cervical vertebrae injuries and usually result from a severe hyperextension or hyperflexion of the head and the neck. Common causes of these types of injuries are car accidents, diving in shallow waters, falls from horses, and football. If the hyperextension is severe enough, a fracture of C2 can occur. When combined with a rupture of the anterior longitudinal ligament and adjacent intervertebral discs, where the skull, C1, and C2 are separated from the rest of the spinal column, the spinal cord can be severely damaged. In these cases, the damage is usually fatal or severely catastrophic. Less severe damage can result in a range of pain and weakness symptoms that range from vague aches to loss of sensory and motor functions.