If you would understand anything, observe its beginning and its development.
—Aristotle
Understanding the unique features in the anatomy of neck makes the study of neck more interesting. Cervical spine consists of 7 vertebrae (Fig. 1.1). Each has distinct features.
The junction between C1 and occiput is the craniovertebral (CV) junction. CV junction anomalies are a distinct entity in neurology practice, e.g. Arnold-Chiari malformation. The junction between C7 and D1 is the cervicothoracic junction. This is an important landmark in chiropractic.
ANATOMY OF CERVICAL VERTEBRA
Cervical vertebrae are the smallest of the movable vertebrae. Stability of the cervical spine is maintained by the ligaments. The cervical spine has a normal curvature. This is known as cervical lordosis. Obliteration or reversal of this curve indicates pathology.
These are small joints between the bodies of vertebra. Uncovertebral joint is one of the earliest site to be involved in spondylosis.
Foramen in the Cervical Spine
Intervertebral Foramen (Fig. 1.4)
The intervertebral foramen transmits the spinal nerve. Osteophyte or disc can cause compression of nerve at this site (foraminal compression) This causes radiating pain along the corresponding dermatome (brachialgia).
Foramen Transversorium (Fig. 1.5)
Foramen transversorium is in the transverse process of C2-7 vertebrae transmits the vertebral artery which supplies the midbrain and takes part in the formation of Circle of Willis in the brain. (Fig. 1.6)
C1 vertebra is called atlas because it supports the head. It is ring shaped and has no spinous process (Fig. 1.7). The transverse ligament divides the ring into 2 parts. The anterior part is occupied by the odontoid process. The posterior part is occupied by the spinal cord. (Fig. 1.8). The transverse processes are longer than those of other vertebra and act as levers for rotatory muscles of the head.
C 2 vertebra is called axis (Figs 1.9 and 1.10): The odontoid process or odontoid peg is the chief feature.
Hangman's fracture is fracture of bilateral pars interarticularis of C2 and disruption of C2,3 junction.
Fig. 1.8: CT of cervical spine transverse section at the level of atlas: Odontoid process of axis is seen occupying the anterior portion
C7 Vertebra
It has a prominent spinous process which ends in a single tubercle which is called the vertebra prominens (Fig. 1.11). This is the most easily palpable cervical spine. The anterior part of the transverse process of C7 vertebra may develop as a “cervical rib”.
Cervical Spinal Canal (Fig. 1.12)
The spinal cord lies inside the spinal canal. Normal anteroposterior diameter of canal is 17 to 18 mm at C3-5 level and 12 to 14 mm at C6-7 level.
Diameter less than 10 mm is called “canal stenosis”. Diameter of 10 to 13 mm is relative canal stenosis. A prolapsed disc will further compromise the space available for cord and cause cord compression. Canal diameter more than 13 mm usually causes no symptoms.
Canal diameter is best measured by MRI or CT.
MOVEMENTS OF THE NECK
There are basically four sets of movements of the neck.
- Anteroposterior gliding motion.
- Right and left rotation as you nod for “No”. This occurs at the atlantoaxial joint.
- Right and left lateral flexion (Fig. 1.15).
Many movements in day-to-day life do not strictly follow a single plane but are usually three dimensional—a combination of flexion/extension with lateral flexion and rotation.
MUSCLES OF THE NECK
The movements of the neck are controlled by several groups of muscles. It is useful to classify these muscles into anterior, posterior and deep posterior muscles.
These muscles are also the most common source of pain such as in Myofascial pain syndromes. Trigger points causing pain, etc. It is worthwhile to remember 10 out of the 18 points tender of fibromyalgia are centered in the muscles of the neck.
Anterior Neck Muscles
Sternocleidomastoid causes rotation and lateral flexion and assists in extension of the neck. Scalene muscles cause lateral flexion of the neck (Fig. 1.16).
Posterior Neck Muscles
These include several muscles running between the different spines (splenius, cervicis semispinalis cervicis, etc.), between the spines and the head or caput (splenius capitis, semispinalis capitis, etc) and the multifidus muscle. They are responsible for a variety of movements including extension, rotation, lateral and flexion.
Normally, the cervical spine column is aligned like a ‘C’ (the normal lordosis). Spasm in the posterior neck muscles causes reversal or obliteration of the lordosis or straightening of spine, which can be appreciated in the lateral view X-ray of the cervical spine.
Fig. 1.16: Neck rotation: Anterior neck muscles white arrow—scalene muscle; red arrow—sternocleidomastoid muscle
Deep Posterior Muscles
They run between C1, C2 and the caput. The deep muscles are located in the suboccipital triangle, e.g. rectus capitii and oblique muscles of the head. They contain abundant stretch receptors (muscle spindles) which are responsible for posture control.
SPINAL CORD
C1-T1 segments of the spinal cord are present in the cervical spine.
Cross section of the spinal cord shows the following tracts:
Corticospinal, extrapyramidal, posterior column, anterior and lateral spinothalamic tract (Fig. 1.17).
- C1 spinal nerve has no sensory supply.
- C2 forms the greater occipital nerve supplying the scalp. Compression of this nerve may cause headache.Phrenic nerve is from C4 segment and supplies the diaphragm. This is the reason why high cervical lesions can cause respiratory embarrassment.
- C5-T1 spinal nerves supply the upper limb through the brachial plexus (Fig. 1.18)
CRANIAL NERVES
V Nerve (Fig. 1.19)
Spinal tract of trigeminal nerve is a sensory tract. It emerges from the Pons and extends to upper cervical cord. This is the reason why upper cervical disc lesions can present with features of sensory disturbances in the face.
XI Nerve
Spinal accessory nerve. The spinal nucleus is situated in the cervical spinal cord and the cranial nucleus in the lower medulla. It supplies the sternocleidomastoid muscle and trapezius.
Craniovertebral junction
It is the junction between C1 and the occiput. Many congenital anomalies are known to occur here.
Fig. 1.19: Sagittal section through brainstem and cervical spinal cord showing nucleus of cranial nerves V
Fig. 1.20: MRI of brain and craniovertebral junction. Arnorld-Chiari malformation type I. Arrow: Herniation of cerebellar tonsil into foramen magnum
The cerebellar tonsils is closely related to the foramen magnum and C1 vertebra. Herniation of cerebellar tonsils into the foramen magnum and cervical spinal canal leads to various types of Arnold-Chiari malformation (Fig. 1.20), which presents with ataxia, spastic weakness of all four limbs and incontinence.
SUGGESTED READING
- Agur AMR, Lee Ming J, Grant JC Boileau. Grant's Atlas of Anatomy, 11th edn. Lippincott Williams and Wilkins; 2005.
- Giles LGF, Singer KP (Kevin P). Clinical Anatomy and Management of Cervical Spine Pain. Butterworth-Heinemann; 1997.
- Last RJ. Regional and Applied Anatomy, 9th edn. Churchill Livingstone; New York: 1990.