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Biomechanics Cervical Spine

Spine: cervical vertebral column

Cervical Spine

Two anatomically and functionally distinct segments

  1. Superior or Sub-Occipital segment

Atlas & Axis.

These vertebrae are connected to each other and to the occiput by a complex chain of joints with three axes and three degrees of freedom.

2. Inferior segment

Stretching from the inferior surface of the axis to the superior surface of T1.

  • are all alike.
  • The joints of the inferior segment have only two types of movements:
  • Flexion and extension, and lateral flexion with rotation

Functionally segments


3rd Cervical vertebra

Rotation at the atlanto-axial and atlanto-odontoid joints


Atlanto-Axial joint  Flexion – extension at the atlanto-axial and atlanto-odontoid joints


Atlanto-occipital joints


This rotation of the occiput is not simple as it actively stretches some ligaments, particularly the Lateral Atlanto-Occipital Ligament (L).

This rotation is associated with an anterior displacement of the right occipital condyle on the right lateral mass of the atlas, but at the same time the lateral atlanto-occipital ligament (L) wraps itself around the odontoid and is stretched.

The tension developed in this ligament pulls the right occipital condyle to the left.

Therefore rotation of the occiput to the left is associated at once with a linear displacement of 2 to 3 mm to the left and lateral flexion to the right.

Lateral flexion & flexion and extension at the atlanto-occipital joint

During lateral flexion

There is no movement at the atlanto-axial joint.

Movement occurs only between the axis and C3 and between the occiput and the atlas.

Between the occiput and the atlas movement consists only of the slipping of the occipital condyles to the right during flexion to the left and vice versa in flexion to the right; there is a small range of movement.

During flexion and extension of the occiput on the atlas the occipital condyles slide on the lateral masses of the atlas.

During flexion, the occipital condyles recede on the lateral masses of the atlas and,
at the same time, the occipital bone moves away from the posterior arch of the atlas. As the latter movement is always associated with extension in the atlanto-axial joint the posterior arches of the atlas and axis become more widely separated.

Flexion is limited by the tension developed in the articular capsules and the ligaments (the posterior atlanto-occipital membrane and the posterior cervical ligament).

During extension, the occipital condyle slide anteriorly on the lateral masses of the atlas.
At the same time the occipital bone moves nearer to the posterior arch of the atlas and, as the Atlanto-axial joint is also extended, the posterior arches of the atlas and axis are approximated.

Extension is limited by the impact of these three bony pieces.
During forced extension the posterior arch of the atlas can be caught as in ‘a nutcracker and fractured.

Atlanto-Occipital Joint

The total range of flexion and extension is 15° at the Atlanto-Occipital joint

The suboccipital vertebral ligaments

The cruciate ligament, consisting of the transverse ligament (3), shown transected here and lying against the posterior articular facet of the odontoid (i); the transversa-occipital ligament (4) between the superior border of the transverse ligament and the basi-occiput; the transverso-axialligament (5) between the inferior border of the transverse ligament and the posterior aspect of the body of the axis.

The apical ligament of the odontoid process (1), very short and thick, runs from the apex of the odontoid to the basi-occiput.

The median oecipico-axial ligament (7), posterior to the cruciate ligament, runs from the basi-occiput to the body of the axis. It is continuous laterally with the lateral occipito-axialligament.

The capsular ligament of the atlanto-occipital joint (9).

The posterior longitudinal ligament (12), lying posterior to the median and lateral occipito-axial ligaments, runs from the gutter in the basi-occiput” to the sacral canal.

The anterior atlanto-occipital membrane (16) is continuous inferiorly with the apical ligament of the odontoid. It is made up of an anterior (13) and a posterior (14) band and runs from the inferior aspect of the occiput to the anterior aspect of
the anterior arch of the atlas.

The anterior atlanto-axial ligament (16) is continuous inferiorly with the anterior atlanto-occipital membrane. Thus the fibroadipose space, containing the atlanto-odontoid joint and its capsule (17), is bounded anteriorly by the odontoid and its apical ligament, and Posteriorly by the anterior atlanto-occipital membrane and the atlanto-axial ligament.

The anterior longitudinal ligament (IS) lies anterior to all these ligaments, arises from the inferior surface of the basi-occiput, bridges over the anterior arch of the atlas without any attachment and gains insertion into the anterior aspect of the body of the axis (18′).

The posterior arches are linked by the following ligaments

The posterior atlanto-occipital membrane (19) runs from the posterior margin of the foramen magnum and the posterior arch of the atlas and is the homologue of the ligamentum flavum. It is pierced just posterior to the lateral masses of the atlas by the occipital artery and the first cervical nerve;

the posterior atlamo-axial ligament (21) runs between the posterior arches of the atlas and axis like a ligamentum ftavum.

It is pierced just posterior to the atlanto-axial joint by the second cervical nerve

The ligamentum nuchae (22) connects all the cervical spines with one anqther, including those of the atlas and the axis.

The posterior cervical ligament (23), a thick fibrous band, is analogous to a Supraspinous ligament. It is attached superiorly to the squama of the occiput in the midline and divides the muscles of the neck into a right and a left compartment.
The capsular ligament of the joint between the articular process of the axis and C3 (24) lies posterior to the intervertebral foramen which lodges the third cervical nerve.
A ligamemum Flavum (29) connects the posterior arches of the axis and C3.


The occipital condyles (c).

The lateral masses of the atlas (d).

The joints between the inferior articular facets of the lateral masses of the atlas (1).

superior articular facets of the axis (m).

Pedicle and of the articular process of the axis (t).

Deep plane

  • Apical ligament of the odontoid (1).
  • Two alar ligaments of the odontoid (2).
  • Transverse ligament (3).
  • Transverso-occipital ligament (4).
  • Transverso-axial ligament (5).

 Intermediate Plane

In the midline, the crucial ligament (6) made up of:

Transverse Transverso-occipital Transverso-axial ligaments

Laterally: the capsular ligament of the occipito-axial joint (9), reinforced laterally by the lateral atlanto-occipital ligament (10) ; inferiorly, the capsular ligament of the atlanto-axial joint (11) ;

 Superficial Plane

Median Occipito-axial ligament (7) continuous on both sides with the lateral occipito-axial ligaments (8).

Posterior longitudinal ligament (12).

 Bone Structures Anterior Ligaments

The anterior atlanto-occipital membrane with its deep layer (13) and its superficial layer (14).

Capsule of the atlanto-occipital joint (9).

Anterolateral atlanto-occipital ligament (15), lying anterior to the former and running obliquely from the basi-occiput to the transverse process of the atlas.

Anterior atlanto-axial ligament (16), continuous laterally with the capsular ligament of the atlanto-axial joint (11).

Anterior longitudinal ligament (18).

Capsular ligament of the joint between the axis and C3 (23).

Posterior arches of the atlas, axis and C3 , the vertebral canal and the foramen magnum between the occiput and the axis.

Left side of image:

Posterior atlanta-occipital ligament (19), with the lateral atlanto-occipital ligament (20).

Posterior atlanto-axial ligament (21).

Ligamentum nuchae (22), strengthened by the posterior cervical ligament, shown here only on
the left side.

Capsular ligament of the joint between the axis and C3 (24). First cervical nerve (26) as it emerges through the foramen for the vertebral artery and the second cervical nerve (27), whose posterior ramus gives off the greater occipital nerve.


Right side of image:

The occipito-axial ligaments, median (7) and lateral (8).

Capsular ligament of the occipita-axial joint (9) strengthened by the lateral atlanta-occipital ligament (10).

Also seen is the vertebral artery.

Ligaments vector  Structure of a typical cervical vertebra

Ligaments of the lower cervical vertebral column

  • Anterior longitudinal ligament
  • Posterior longitudinal ligament
  • Interspinous ligament
  • Supraspinous ligament
  • Intertransverse ligaments

Flexion and extension


During flexion

The upper vertebral body tilts and slides anteriorly, compressing the intervertebral space anteriorly and driving the nucleus posteriorly and stretching posterior fibres of the annulus.

During extension

The upper vertebral body tilts and slides posteriorly, compressing the intervertebral space posteriorly and driving the nucleus anteriorly and stretching anterior fibres of the annulus.

Unco-vertebral joints (joints of Luschka)

During flexion-extension the unco vertebral facets slide, and the processes ‘guide’ the vertebral body.

During lateral flexion one side the interspace open out, and slides on the contralateral side. The movements are far more complex, and the flexion is not pure, is always associated with rotation and extension.

 The orientation of the articular facets:

the composite axis of combined rotation and lateral flexion

superior and inferior surfaces of these facets are not strictly flat but are slightly convex posteriorly between C6 and C7 (A) or slightly concave posteriorly between C3 and C4 (B).


Combined lateral flexion and rotation in the lower cervical vertebral column

Frontal plane (F) corresponds to lateral flexion.
Sagittal plane (S) corresponds to extension.
Transverse or horizontal plane (H) corresponds to rotation.

 Suboccipital Cervical Column

Vertical axis, corresponding to the odontoid, and allowing rotation and some flexion and extension of the elliptical plateau representing the atlas.

Small complex, corresponding to the atlanto-occipital joint, with a vertical axis passing through the centre of the plateau of the atlas.

As a whole the suboccipital vertebral column is the equivalent of a joint complex with three axes and three degrees of freedom.

Lower cervical column

Between C2 and T1 only the composite movements of lateral flexion and rotation are possible.

The vertebral bodies themselves limit lateral flexion and rotation.

 Compensations in the suboccipital vertebral columnDuring Pure Rotation

During pure rotation of the head to the right, the complementary rotation of the suboccipital vertebral column to the right is achieved by the following muscles:

– Right obliquus capitis inferior and rectus capitis posterior major and the left obliquus capitis superior.

These muscles all extend the head and bring about the extension mentioned above. The contralateral flexion to the left is achieved by the left obliquus capitis superior, the left rectus capitis lateralis and the left rectus capitis posterior minor.

During Pure Lateral Flexion of the head to the right and counter-rotation to the left

Achieved by the following muscles:

– Left obliquus superior and the two posterior recti and lateral flexion to the right by the two posterior recti and the inferior oblique on the right side.

Finally the extension caused by these muscles as well as the extension in the lower cervical column and the extension that would follow counter-rotation to the left are compensated for by the flexor muscles: the right rectus capitis anterior and the rectus capitis lateralis.



Lower cervical vertebral column, which shows a composite movement of rotation, lateral flexion and extension.

Suboccipital vertebral column which consists of a joint complex with three axes and three degrees of freedom and controlled by the fine tuning of the suboccipital muscles.

Range of movements of the cervical vertebral column

Total range of flexion & extension in:

  • Lower cervical column is 100-110°
  • Suboccipital column is 20-30°
  • Whole cervical column is 130°.

Total range of lateral flexion is about 45°.

Total range of rotation of the head varies from 80-90° on either side.
It amounts to 12° at the atlanto-occipital joint and at the atlanto-axial joint.

 Rotation Balancing of the head Structure and action of the sterno-cleido-mastoid (SCM)

Is made up of four distinct bands:

Deep band, the Cleido-mastoid (CM) running from the medial third of the clavicle to the mastoid process

Three superficial bands:

  1. Cleido-Occipital in the lateral third of the superior nuchal line of the occipital.
  2. Sterno-Occipital from sternum to superior nuchal line
  3. Sterno-Mastoid, from sternum to Mastoids.

Unilateral contraction: triple movement:

  1. Rotation of the head contralaterally
  2. Lateral flexion ipsilaterally
  3. Extension

Bilateral contraction:
If cervical vertebral column is flexible, accentuates the cervical lordosis with extension of the head and flexion of the cervical column relative to the thoracic column.

If cervical column is kept straight and rigid by prevertebral muscles, then produces flexion of the cervical column relative to the thoracic column and forward flexion of the head.

 The Prevertebral muscles: the longus cervicis

Deepest of the prevertebral muscles, from the superior arch of the atlas to the third thoracic vertebra, covers the whole anterior surface of the cervical column

Three sets of fibres anatomically:

1) Oblique descending

2) Oblique ascending

3) Longitudinal

When both muscles contract symmetrically they flatten the cervical curvature and flex the neck.
They are also important in stabilizing the cervical column at rest. Contraction of one muscle produces forward and lateral flexion of the cervical column ipsilaterally.

Longus cervicis

The prevertebral muscles: the anterior and lateral rectus muscles

Rectus Capitis Anterior with 2 bands:

Deep (anterior major) and superficial (anterior minor).
Bilateral contraction produces flexion of the head on the cervical column and a flattening of the lordosis of the upper portion of the cervical column. Unilateral contraction causes forward and lateral flexion of the head ipsilateral.

Rectus capitis lateralis: intertransverse muscles attached to the jugular process of the occiput and to anterior tubercle of the transverse process of the atlas.
Bilateral contraction produces flexion of the head on the cervical column, its unilateral contraction produces a slight lateral flexion of the head ipsilaterally. Both these movements occur at the atlanto-occipital joint.

 Prevertebral muscles: scalene muscles

1) Scalenus anterior (s.a.) origin from transverse processes of C3-C6, inserts in the first rib.

2) Scalenus medius (s.m.) origin in transverse processes of C2- C7, to the first rib just posterior to the groove for the subclavian artery.

3) Scalenus posterior (s.p.) Origin from the transverse processes of C4 – C6, to the second rib.

Between the anterior and middle scalenes run the roots of the brachial plexus and the subclavian artery.

When these muscles contract symmetrically the cervical column is flexed on the thoracic column and the cervical lordosis is accentuated if the neck is not held rigid by contraction of the longus cervicis. On the other hand, if the cervical column is held rigid by the longus cervicis, symmetrical contraction of the scalenes can only flex the cervical column on the thoracic column.

If the scalenes contract only on one side the cervical column is laterally flexed and rotated towards the side of their contraction.

They are also accessory inspiratory muscles as they can elevate the first two ribs when their cervical vertebral attachments are kept steady.

 Prevertebral Muscles Summary

Longus cervicis (l.c.)

Rectus capitis anterior

Rectus capitis lateralis (r.l.)

Inter transverse muscles (flexion only) anterior (i.t.a.) and posterior (i.t.p.)

Scalenus anterior (s. a.) Scalenus medius (s.m.) Scalenus posterior (s.p.)

 Flexion of the head and neck

Flexion of the head on the cervical column and flexion of the neck on the thoracic column depend on the anterior muscles of the neck.

a) In the suboccipital region the rectus anterior (r.a.) produces flexion at the atlantooccipital joint.

The longus cervicis (l.C.1 and L.C.2 ) and the anterior rectus produce flexion at the lower vertebral joints.
It must be stressed that the longus cervicis plays the most important role in straightening the cervical column and holding it rigid.

B) Supra-Hyoid muscles: as mylo-hyoid and the anterior belly of the digastric.

C) Infra-Hyoid muscles: as thyrohyoid, the sterno-hyoid (s.h.), the sterno-thyroid.

 Posterior muscles of the neck

Deep plane
running between the occiput, the atlas and the axis.

  • Rectus Capitis Posterior major (1) & Minor (2)
  • Obliquus Capitis Superior (3) and inferior (4) & Lateralis Cervical Transverso-spinalis (5)
  • Interspinous muscles (6)

Rectus Capitis Posterior Major

Rectus Capitis Posterior Minor

Obliquus Capitis Superior

Obliquus Capitis Inferior

Obliquus Capitis Lateralis

 Posterior muscles of the neck

Semispinalis plane:

  • Semispinalis capitis (7)
  • Semispinalis cervicis (8) laterally


  • Transversus thoracis
  • Longissimus thoracis
  • Iliocostalis (11)

Plane of the splenius and the levator scapulae:

Two layers:
Splenius Capitis (9)

Splenius Cervicis (10)

Levator Scapulae

Skull base Posterior muscles of the neck

Superficial Plane:

  • Trapezius
  • Sterno-Cleido-Mastoid


 Muscles  of the neck: SUMMARY

On the whole, except for the deep muscles, the majority of these muscles are oblique inferiorly, medially and posteriorly and so produce simultaneously extension, rotation and lateral
flexion towards the side of their contraction.

Intermediate muscles run inferiorly, anteriorly and laterally. In counter direction to superficial muscles.

Thus they produce extension and lateral flexion ipsilaterally, like the deeper muscles, but rotation contralaterally.

The suboccipital muscles

  1. Rectus Capitis Posterior Major
  2. Rectus Capitis Posterior Minor
  3. Obliquus Capitis Superior
  4. Obliquus Capitis Inferior
  5. Interspinous muscles

Actions of the suboccipital muscles: lateral flexion and extension

Obliquus Capitis Inferior

The obliquus capitis inferior, is important in maintaining the integrity of the atlanto-axial joint at rest and during movements.

This muscle pulls back the transverse processes of the atlas and so, when the two obliques contract symmetrically, they pull back and extend the atlas on the axis. When they contract symmetricalty they pull the axis forward arid as a result the atlas moves backwards over a distance.

This relieves the tension in the transverse ligament, which passively holds the odontoid and prevents its posterior dislocation.

Thus these two muscles acting simultaneously are essential in maintaining the integrity of the atlanto-odontoid joint during activity.

Unilateral contraction of the four suboccipital muscles produces lateral flexion of the head ipsilaterally at the atlanto-occipital joint.

The most efficient of these muscles is:

1) Superior Oblique
2) Rectus Posterior Major
3) Superior Oblique
4) Rectus Minor is minimal efficient.

Bilateral simultaneous contraction of the suboccipital muscles produces extension of the head on the upper cervical column.

At the atlanto-occipital joint Muscles involved:
Rectus Posterior Minor (2) and the superior oblique (4). At the atlanto-axial joint muscles involved:
Rectus posterior major (1 ) and the Inferior Oblique.

 Rotatory action of the suboccipital muscles

In the atlanto-Occipital joint, the superior oblique muscle (4) produces a 10° rotation of the head contralaterally, for example:

The left superior oblique rotates the head to the right. This passively stretches the inferior oblique (4) and the rectus posterior minor (2) on the right side and these muscles restore the head to the neutral position.

Rotation of Atlanto-Occipital joint

In the atlanto-Axial joint, the Rectus Posterior Major and Inferior Oblique produces rotation of the head ipsilaterally.

The Rectus Posterior on Atlanto – Axial and Atlanto-Occipital, the Inferior Oblique only in the Atlanto-Axial.

The opposite left Rectus Major stretches will restore the head to the neutral position.

Rotation of Atlanto-Axial Joint

Extensors Deep to the trapezius is the 3rd muscular plane

  • Splenius Capitis (9)
  • Splenius Cervicis (1O)
  • Levator Scapulae (12)

Extensors 2nd muscular plane

  • Semispinalis Capitis (7)
  • Longissimus Capitis (8)
  • Semispinalis Cervicis (11)
  • Cervicai portion of the Ilio-Costalis (11′)


Extension Deep Muscles

Group I:

  • Splenius Cermcis (10)
  • Semispinalis Cervicis and the cervical portion of the ilio-costalis (11)
  • Levator Scapulae (12)

Extension Deep Muscles

Group II:

  • Transverso-spinalis
  • Semispinalis capitis (7)
  • Longissimus capitis (8)
  • Splenius Capiti

Extension Deep Muscles

Group III:

  • Trapezius
  • Sterno-Mastoid

 Stability of the cervical column in the sagittal plane Cervical Muscles Synergism Coupled Motion

Cervical Spine

Automatic rotation of the vertebral column during lateral flexion

Spines move in to convexity

Lumbar Spine

Automatic rotation of the vertebral column during lateral flexionSpines move into concavity


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