Functional Anatomy of the Cervical Spine

Introduction

The cervical spine supports and promotes movement of the head and neck. 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. Considering the small weight-bearing load of the cervical spine, large vertebral bodies are not required. In this section of the spine, vertebral size is not as important as flexibility and range of motion. Increased movement correlates to a heightened injury potential of the spinal cord and its associated neurovascular structures.

Cervical Spine Vertebral Bodies

C spine	C3-C6	Atlas	Axis	C7
Features	triangular vertebral foramen bifed spinous process transverse foramina (space for nerves and vasculature	no spinous process no vertebral body	odontoid process (dens) extending superiorly from anterior portion of the vertebra	singular spinous process larger spinous process
Articulations	.	occiput via superior and inferior facets axis through lateral masses	anterior arch of the atlas

Joints of Cervical Spine

Joints	Disc Joint	Facet Joint or Zygapophyseal joints	Uncovertebral	Atlanto-axial	Atlanto-occipital
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

Intervertebral Disc (IVD)

In general, 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 gives the advantage of greater range of motion potential. Disks are thicker anteriorly than posteriorly to enable the lordotic curvature of the cervical spine. The nucleus pulposus of cervical discs dries out by the age of 30 to a firm, fibrocartilaginous plate.

• Coronal plane
  • concave superior surface
  • convex inferior surface to conform to adjacent vertebral bodies
  • movement limited by uncinate process
  • anteroposterior translation does occur

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

• Cartilaginous endplate
  • composed of hyaline cartilage
  • located adjacent to the subchondral bone.
  • serves as a barrier to nucleus pulposus pressure on the vertebral body
    • limiting protrusion

Cervical Lordosis

Lordosis = the natural curve for the lumbar spine. This curve defines lumbar spine alignment in the saggital plane. However, the pelvis is "the cornerstone of spinal sagittal alignment". The curve of the sacrum determines the lumbar curve.

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Bones, Articulations and Kinematics of the Lumbar Spine

Kinematics

The lumbar spine is considered a three-joint complex or an articular triad. The zygapophyseal (facet) joints and intervertebral disc joint are part of a "spinal motion segment". The various parts of the spinal motion segment work together to allow spinal motion and to protect the spine from excessive movements.

The spinal motion segment has the following characteristics:

• The intervertebral disc joint transmits mostly vertical compressive loads
• The facet joints guide and stabilise the motion segment
• In an erect standing position and erect sitting posture, spine load is also transmitted through the facet joints

Joint	Type of joint	Plane of movement	Motion	Kinematics	Closed pack position	Open pack position
Intervertebral disc joint	Cartilaginous joint, symphysis	A single joint: structurally fused but allows very limited, multidirectional movements All lumbar intervertebral disc joints and zygapophyseal joints combin	Full extensexion:60 degrees Extension 25 degrees Lateral flexion 20-30 degrees Rotation 1-5 degrees	Full extension	Halfway between flexion and extension

Spinal Ligaments

• Nuchal ligament – a continuation of the supraspinous ligament. It attaches to the tips of the spinous processes from C1-C7, and provides the proximal attachment for the rhomboids and trapezius.

• Transverse ligament of the atlas – connects the lateral masses of the atlas, and in doing so anchors the dens in place.

(Note: Some texts consider the interspinous ligament to be part of the nuchal ligament).

Key ligaments	Origin	Insertion	Action/role	Key palpation points
Anterior longitudinal ligament	The anterior portion of the vertebral body at the base of the skull	The anterior portion of the vertebral body at the sacrum	Limits extension of the vertebral column. Reinforces the intervertebral disc.
Posterior longitudinal ligament	The body of C2	Posterior surface of the sacrum	Limits flexion of the vertebral column. Reinforces the intervertebral disc.
Ligamentum flavum: A series of short ligaments that connect the laminae of each vertebra. There are two ligamenta flava at each vertebra. Each ligament is divided into: The medial portion: passes to the back of the next lower lamina and across the gap between the adjacent vertebrae, fusing with the interspinous ligament The lateral portion: passes in front of the facet joint, attaches to the anterior aspect of the inferior and superior articular processes and forms the anterior capsule. The most lateral fibres extend beyond the superior articular process to the pedicle below.	The lower half of the anterior surface of the lamina above	The posterior surface and upper margin of the lamina below	Their high elastin content prevents the ligament from buckling into the spinal canal. Assists with lumbar spine flexion and extension. Compresses the intervertebral discs.
Intertransverse ligaments	Transverse processes of the vertebra above	Transverse processes of the vertebra below	Contributes to the stability of the lumbar spine. Limits lateral flexion.	To palpate the transverse process, position the patient in sitting. The transverse processes of the lumbar spine are most likely located directly in line with the spinous process of the corresponding vertebra. Start by palpating the spinous process of the L1 vertebra and move directly lateral to find the transverse process of L1.
Supraspinous ligament	Tip of spinous processes of the vertebra above from the seventh cervical vertebra to the third or fourth lumbar vertebra	Tip of spinous processes of the vertebra below	Prevents the separation of the spinous processes during forward flexion, thus limiting lumbar spine flexion	You can palpate the spinous processes in the centre of the patient's back. Start with finding T12 by palpating the patient's lowest rib and following your finger along the border of the rib towards the centre of the spine.T12 spinous process is in line with the 12th rib that inserts into the spinal segment. Below T12, you can palpate L1 and continue along the spinous process of L2, L3, and L4.
Interspinous ligament	Spinous processes of the vertebra above between the ligamenta flava anteriorly and the supraspinous ligament posteriorly	Spinous processes of the vertebra below between the ligamenta flava anteriorly and the supraspinous ligament posteriorly	Limits forward flexion of the vertebral column.
** special to C-Spine Nuchal ligament	occiput	tips of the spinous process from C1-C7	limit hyperflexion	proximal attachment for rhomboids and trapezius
** special to C-spine Transverse ligament		connects lateral masses of atlas	anchors dens in place
** special to C-spine Apical ligament	dens of the axis	foramen magnum	stabilises skull on spine
** special to C-spine Lar Ligament	dens of the axis	occiput	limits atlanto-axial rotation
** special to C-spine cruciform or cruciate ligament 1. superior longitudinal band 2. inferior longitudinal band, 3. transverse band.	superior: transverse band inferior: transverse band transverse ligament: dens of axis	superior: foramen magnum second vertebral body transverse ligament: between lateral masses of atlas	hold dens in place

Ligaments Unique to Cervical Spine

Ligament	Origin	Insertion	Role/Function	Key Palpation Points
Nuchal ligament	occiput	tips of the spinous process from C1-C7	limit hyperflexion	proximal attachment for rhomboids and trapezius

Muscles of the Lumbar Spine and Abdominal Wall

The muscles of the back can be grouped according to their function and location.

When grouped according to function, the muscles of the lumbar spine can be organised as follows:

• Flexors: psoas major, psoas minor, internal oblique, external oblique, and rectus abdominis
• Extensors: quadratus lumborum, interspinales lumborum, multifidus, and the erector spinae (iliocostalis, longissimus)
• Lateral flexors: intertransversarii lumborum, psoas major, quadratus lumborum, erector spinae, internal and external obliques
• Rotators: multifidus, internal and external obliques

When grouped according to location, the muscles of the lumbar spine can be divided as follows:

• The intrinsic (deep) group:
  • Superficial layer: erector spinae muscles
  • Middle (deep) layer: multifidus
  • Deepest layer: interspinales lumborum and intertransversarii lumborum
• The abdominal wall group: transverse abdominis, the internal oblique, rectus abdominis, and the external oblique
• The hip group: psoas major, psoas minor, quadratus lumborum

The following tables group muscles according to their function. Please note, that when a muscle has multiple functions, it is included in all relevant tables. These tables only list muscle actions associated with the lumbar spine and abdominal wall. If a muscle acts on other joints, these actions are discussed on the relevant page. For example, psoas major is also a major hip flexor - this role is detailed on the Functional Anatomy of the Hip page.

Lumbar Spine Flexors

Muscle	Origin	Insertion	Innervation	Action

Lumbar Spine Extensors

Muscle	Origin	Insertion	Innervation	Action

Lumbar Spine Lateral Flexors

Muscle	Origin	Insertion	Innervation	Action

Lumbar Spine Rotators

Muscle	Origin	Insertion	Innervation	Action

Innervation of the Lumbar Spine and Abdominal Wall

Nerve	Origin	Branches	Motor fibres	Sensory fibres

Vascular Supply of the Lumbar Spine and Abdominal Wall

Artery	Origin	Branches	Supply

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.

(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.