Cervical spine

Cervical vertebrae

The cervical spine consists of seven vertebrae, of which four are typical (C3 to C6) and three are atypical (C1, C2 and C7) ( Fig. 32.1 ). A typical cervical vertebra has a small, relatively broad vertebral body. The superior surface of the body is saddle-shaped, with flange-like lips, the uncinate processes, arising from most of its lateral circumference and articulating with the inferior aspect of the vertebra above, forming the uncovertebral joints (joints of Luschka). The anterior surface of the body is concave from above down. Several vascular foramina on the posterior surface of the body transmit basivertebral veins to the anterior internal vertebral plexus. The pedicles project posterolaterally and the laminae project posteromedially, enclosing a large, roughly triangular vertebral canal that accommodates the cervical enlargement of the spinal cord. The spinous process is short and typically bifid. Lateral to the body, each transverse process contains a foramen transversarium that normally transmits the vertebral artery, vertebral venous plexus and a branch from the cervicothoracic ganglion (vertebral nerve). The intervertebral foramina are bounded by the pedicles superiorly and inferiorly, posteriorly by the facet joints, and anteriorly by the unco­vertebral joint and intervertebral disc.

The first cervical vertebra (C1, atlas) is a ring of bone consisting of two lateral masses connected by a short anterior and a longer posterior arch; it lacks a body and spinous process. The anterior arch is slightly convex anteriorly, and carries a roughened anterior tubercle to which the anterior longitudinal ligament is attached. Its upper and lower borders provide attachment for the anterior atlanto-occipital membrane and diverging lateral parts of the anterior longitudinal ligament. The posterior surface of the anterior arch carries a concave, almost circular, facet for articulation with the dens of the axis at the median atlanto-axial joint. The lateral masses are ovoid, their long axes converging anteriorly. Each bears a kidney-shaped superior articular facet for articulation with the respective occipital condyle. The inferior articular facet of the lateral mass is almost circular and is flat or slightly concave; it articulates with the axis at the lateral atlanto-axial joint. The posterior arch forms three-fifths of the circumference of the bony ring. Its superior surface bears a wide groove for the vertebral artery, venous plexus and the first cervical ventral ramus, which emerges above the posterior arch of the atlas and passes forwards lateral to its lateral mass and medial to the vertebral artery. The second cervical vertebra (C2, axis) is characterized by a large bifid spinous process and a superior bony projection from the body, the dens (odontoid process). On each side, the foramen transversarium is directed upwards and outwards as the vertebral artery turns abruptly laterally under the superior articular facet to reach the more laterally placed foramen transversarium of C1. The dimensions of the spinal canal are greatest at this level. The seventh cervical vertebra (C7, vertebra prominens) has a long spinous process that ends in a rounded tubercle, and is visible and may be palpated at the lower end of the nuchal furrow. The transverse foramina of C7 usually do not transmit the vertebral artery.

Cervical muscles and ligaments

Broadly speaking, the muscles that form part of the musculoskeletal column in the neck are grouped anterior, lateral or posterior to the cervical vertebrae. The anterior and lateral groups include longi colli and capitis; recti capitis anterior and lateralis; and scaleni anterior, medius, posterior and minimi (when present) ( Fig. 32.2 ); the anterior and lateral group are often referred to as the prevertebral muscles and are innervated by ventral rami of the cervical spinal nerves. The posterior muscle group is composed of the cervical components of the intrinsic muscles of the back, overlaid by some of the extrinsic ‘immigrant’ muscles of the back that run between the upper limb and the axial skeleton (trapezius, levator scapulae) (see Fig. 30.3 ). The intrinsic muscles are arranged in superficial and deep layers and are innervated by medial and lateral branches of the dorsal rami of the cervical spinal nerves. The superficial layer contains splenius capitis and cervicis. The deeper layers include the transversospinal group (semispinales cervicis and capitis, multifidus and rotatores cervicis), interspinales and intertransversarii, and the suboccipital group (recti capitis posterior major and minor, and obliquus capitis superior and inferior).

Of the superficial muscles, trapezius forms the first layer encountered after the skin and fascia are incised. It arises from the external occipital protuberance, the ligamentum nuchae and the spines of all the cervical vertebrae. Upper fibres insert into the lateral third of the clavicle, the middle fibres insert into the medial edge of the acromion and the superior margin of the spine of scapula, and the lower fibres ascend on to the spine of the scapula. Levator scapulae is the next layer. It originates via slips from each of the transverse processes of 1–4 cervical vertebrae and inserts on to the medial border of the scapula. Splenius capitis arises from the mastoid process and the rough surface on the occipital bone just below the lateral third of the superior nuchal line. Its fibres pass downwards and medially to reach the midline: the lower fibres insert into the tips of the spinous processes of the seventh cervical and upper three or four thoracic vertebrae and the intervening supraspinous ligaments. The tendons of the upper fibres interlace in the midline with those of the opposite side in the dorsal raphe of the ligamentum nuchae in the lower half of the cervical region. Splenius cervicis is confluent with splenius capitis but covers more caudal regions of the neck and thoracic region. It arises from the transverse process of the atlas, the tip of the transverse process of the axis and the posterior tubercle of the third cervical vertebra. Its fibres pass downwards and medially, wrapping around the other posterior intrinsic neck muscles, to insert into the third to sixth thoracic spinous processes. Erector spinae lies beneath splenius. It is a large musculo­tendinous mass that differs in size and composition at different vertebral levels. Essentially, it is composed of three main columns (from lateral to medial): the iliocostalis, longissimus and spinalis muscles. Longissimus capitis is a narrow, flat band of muscle that arises from the posterior edge of the mastoid process, under cover of splenius capitis and sternocleidomastoid. It descends across the lateral surface of semi­spinalis capitis and is inserted by a series of tendons into the transverse processes of the lower three or four cervical and upper four thoracic vertebrae. Longissimus cervicis is a long, thin muscle that arises by tendons from the posterior tubercles of the transverse processes of the second to sixth cervical vertebrae. It descends into the thoracic region, between the tendons of longissimus capitis and longissimus thoracis, to insert by tendons into the transverse processes of the upper four or five thoracic vertebrae.

Despite its name, the ligamentum nuchae is not a ligament of the neck, in that it does not connect adjacent bones and lacks the internal structure typical of a ligament: it is a unique arrangement of tendons and fascia between the posterior muscles of the neck. It consists of a dorsal raphe and a median septal portion. The dorsal raphe lies superficially along the posterior midline of the neck, attached to the external occipital protuberance superiorly and the tip of the spinous process of C7 inferiorly. In its superior half it consists of the aggregated tendons of the most medial fibres of the cervical portion of trapezius.

The ligamenta flava connect laminae of adjacent vertebrae in the vertebral canal. Their attachments extend from facet joint capsules to the point where laminae fuse to form spines; the ligaments are thin, broad and long in the cervical region. The spinal cord lies directly beneath the ligamenta flava; the ligaments must therefore be removed carefully in order not to damage the spinal cord and its meningeal coverings. Distinctive interspinous ligaments are not evident at cervical levels, where they are represented by the median septum of the ligamentum nuchae as it passes between the cervical spinous processes. The posterior longitudinal ligament lies on the posterior surfaces of the vertebral bodies in the vertebral canal, attached between the body of C2 and the sacrum.