Supporting structures of cervical spinal segment and need to strengthen these structures

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Spine is considered as the main supporting structure of the body. All the essential ascending and descending nerve tracts to the upper-limbs, lower-limbs and other vital organs are passing through spine. Proper structure and functioning of the spine is essential for efficient working, of person, for prolonged time. Before performing any gross-motor or fine-motor activity, it is prerequisite that the spine should be aligned and adjusted accordingly with respect to the task.

The vertebral column is divided into 5 subtypes namely cervical, thoracic, lumbar, sacral, coccygeal. In today's blog, we will learn about cervical vertebral segment, it's static and dynamic supporting structures and the need to strengthen these structures.

Cervical vertebral column consist of 7 cervical vertebrae and 8 cervical nerves exiting through the intervertebral foramina. 

Supporting structures of cervical vertebral segment : 

These can be divided into skeletal and muscular supporting structural systems. Both systems are essential to support spine during static and dynamic postures. It is essential for therapist to have knowledge of specific or target spine muscles for rehabilitation.

The cervical spine can be divided into the suboccipital (craniovertebral) region and the typical cervical region.

1) The suboccipital region is composed of the occiput, atlas, and superior facets of the axis. The occipital-atlantal joint allows primary motion  of forward and backward nodding (flexion and extension). The atlantal-axial joint allows primary motion of rotation as the atlas pivots around the dens of the axis. This region allows flexion, extension, rotation and side bending motions.

Fig : Atlanto-axial joint

2) The typical cervical region includes the inferior facets of the axis and rest of the cervical spine. It features facet joints that are angled at 45° from the horizontal plane. Another unique feature includes 'joints of Luschka', which are bony projections that provides lateral stability to the spine and reinforce the vertebral disc posterolaterally. These typical cervical vertebrae allows flexion, extension, rotation and side bending motions.

In this article we will focus on muscular supporting system of spine. This system can be divided into inert supporting structures and muscular supporting structures.

A) Inert structures (can also be considered as static stabilizers of spine) : Static stabilizers are the non-contractile tissue of the joint. They are very important in spine stability at end-range ROM and/or when there is a dysfunction of the dynamic stabilizers. Joint capsule and ligaments provides passive resistance to motion. In spine, ligaments are slack in midrange and taut at end range when a structure limits movements in a specific directions and thus provides stability in that direction.

Various inert structures are: (From anterior to posterior)

• Anterior longitudinal ligament
• Anterior Atlanto-occipital membrane
• Apical ligament
• Alar ligament
• Cruciate ligament of the atlas : which includes superior and inferior longitudinal band, and transverse band
• Tectorial membrane
• Posterior Atlanto-occipital membrane
• Ligamentum nuchae
• Ligamentum flavum
• Interspinous ligaments
• Intertransverse ligaments
• Supraspinous ligament

Fig : Static stabilizers of the cervical spinal segment (lateral view)

Fig : Static stabilizers of cervical spine (lateral view)

These inert structures helps to prevent excessive range of motion by becoming taut at end ranges and thus acts as static stabilizers of the cervical spinal segment.

1. Forward bending is limited by interspinous and supraspinous ligament, capsular ligament, ligamentum nuchae, ligamentum flavum, capsule and posterior longitudinal ligament.
2. Backward bending is limited by anterior longitudinal ligament.
3. Side bending is limited by contralateral intertransverse ligament, ligamentum flavum and capsular ligament.
4. Supporting structures of suboccipital region: 
• Cruciate ligaments is important that holds the posterior dens of C2 in the articulation at the Atlanto-axial joint.
• Alar ligament becomes taut in flexion and helps to limit axial rotation and side flexion to the opposite side. It stabilizes C1 and C2 vertebrae, especially in rotation.
• Alar ligament with transverse band of cruciate ligament forms the primary stabilizers of Atlanto-axial joint.
5. Rotation limited by capsular ligament
6. Anterior Atlanto-occipital membrane is a continuation of the anterior longitudinal ligament above C1 level. It limits extension of the atlanto-occipital joint. Posterior atlanto-occipital membrane lies immediately posterior to the spinal theca and continues inferiorly with ligamentum flavum and ligamentum nuchae posteriorly. It limits excessive flexion of the atlanto-occipital joint.
7. Ligamentum nuchae covers spine of C1 to C6 vertebrae. It is the superior and posterior extension of supraspinous ligament. It limits hyperflexion of the neck.
8. Tectorial membrane is a continuation of posterior longitudinal ligament and attaches to the clivus on the anterior half of the
9. Intervertebral discs : it is a shock-absorbing structure between each vertebra. The disc has thick outer layer (annulus fibrosus) that surrounds the soft gel-like center (nucleus). Annulus fibrosus is organized in concentric rings. Some fibers are taut in whichever direction the spinal segment rotates or sheers. Fibers slack on side of concavity and taut on side of convexity. Features of intervertebral disc is that greater the ratio of disc thickness to vertebral height the greater the mobility.

Fig : Supporting structures of cervical spinal segment

B) Muscle structure (also called as dynamic stabilizers) : Dynamic stabilizer is defined as muscles whose isometric or stabilizing contractions maintains control of the functional position in response to imposed fluctuating forces through the moving extremities. Muscular structures of trunk not only acts as a prime movers or as antagonist to movement caused by gravity during dynamic activity, but also provide stability of spine. These muscles crossing the joint is responsible for keeping the opposing joint surfaces in proper alignment for efficient joint mechanics while performing any manual activity.

Various muscles of the cervical segments are:

1) Anteriors surface of neck : 

• Superficial muscles :
• Sternocleidomastoid muscle
• Deep segmental muscles : Provides dynamic support to the cervical spine and head.
• Rectus Capitis Lateralis muscle : craniocervical flexor
• Rectus Capitis Anterior muscle : craniocervical flexor
• Longus Colli muscle : it is an important muscle which performs the action of axial extension (retraction) and works with the sternocleidomastoid (SCM) for cervical flexion. It provides segmental stability to cervical spine. Without the segmental influence of the longus  colli, the SCM would cause increased cervical lordosis when attempting flexion.
• Longus Capitis muscle : deep cervical flexor
• Scalene group : anterior scalene muscle, middle scalene muscle and posterior scalene muscle. The scalene and levator muscles stabilize against the posterior and anterior translatory forces on the cervical spine.

2) Posterior surface on neck :

• Superficial muscles :
• Trapezius : it functions to turn the head and neck in extension and side flexion of neck. This muscle plays an useful role in counterbalancing the pull of gravity on head, as the head tends to be pulled in flexion due to anterior position of centre of gravity. It helps in maintaining the gleno-humeral rhythm. Trapezius and semispinalis capitis counter the weight of the head.
• Levator scapulae muscle : it helps in lateral flexion of neck. Levator scapulae and scalene muscles stabilize against the posterior and anterior translation forces of the cervical vertebrae.
• Deep muscles :
• Semispinalis Capitis : Extension, lateral flexion and rotation of cervical spine.
• Splenius capitis : bilaterally extends the neck. Unilaterally it performs lateral flexion and rotation of head and neck to same side.
• Splenius cervicis : bilaterally extends the neck.  Unilaterally it performs lateral flexion and rotation of head and neck to same side.
• Illiocostalis cervicis : Bilateral action causes extension of spine and unilateral action causes lateral flexion 
• Longissimus Capitis : Bilateral action extends or hyperextends the neck. Unilateral action laterally flexes and rotates the neck to same side.
• Longissimus Cervicis : Bilateral action extends or hyperextends the neck. Unilateral action laterally flexes and rotates the neck to same side.
• Suboccipital muscles : Rectus capitis major, Rectus Capitis minor, Oblique Capitis superior, Oblique Capitis inferior
• Multifidus : it is found on both sides of vertebral column, extending from the cervical all the way down to lumbar spine. Its segmental attachment provides stability and control to movements of the spinal segments.

Fig : Posterior muscles of the cervical segment

Fig : Anterior muscles of the cervical segment

Muscle Control in the cervical spine : 

• The fulcrum of the head on the spine is through the occipital/atlas joints. The center of gravity of the head is anterior to joint axis and therefore has a flexion moment.
• The weight of the head counterbalanced by the cervical extensor muscles (upper trapezius and cervical erector spinae).
• Tension and fatigue experienced in these muscles as well as in levator scapulae (which supports the posture of the scapulae) is experienced by most people who have posture related stress to head and neck.
• The position of the mandible and tension in the muscles of mastication are influenced by the postural relationship between the cervical spine and head.

We need to strengthen and care for static and dynamic structures of cervical segments because any impairments or trauma can lead to cervical spinal nerve impingement or spinal cord compression. Lets have a look on function of cervical spinal nerves : 

• The cervical spine segment allows passage of important vasculature (vertebral artery) to reach the brain via transverse foramen. It provides attachment sites for muscles that move the head, neck and shoulder girdle.
• Branches of C3, C4, C5 spinal nerves forms the phrenic nerve that innervates the diaphragm, enabling breathing. 
• Exiting cervical spinal nerves forms brachial plexus which further divides into roots, trunks and cords to form main branches of musculocutaneous nerve, median nerve, radial nerve, ulnar nerve, axillary nerve. These nerves supplies motor output to upper limb muscles and also receive input signals (sensory sense) from these muscles (includes extrafusal and intrafusal fibers) and superficial sensory receptor.
• C4 - C5 segment is typically more mobile compared to other cervical segments between C2 - C5. The lower cervical segment (C5 - C7) is typically more injured compared to C2 - C5 segment. Although C2 - C5 segment are also susceptible to injury and can cause pain due to degeneration, disc herniation, trauma and neurological injury.
• The C5 - C6 spinal segment provides flexibility and support to much of the neck and the head above. Due to high load bearing function, the C5 - C6 segment is frequently affected by poor posture, degeneration and disc herniation, radicular pain and trauma.

Thankyou for reading!!!!

Dr.Ashwini Sangar, Dr.Pallavi Khadse-Kolhe, Dr.Sheetal Tatar-Dhande