INTIKHAB ALAM 58 SAJJAD AHMAD 29

CONTENTSATLAS AND AXIS

ATLANTO-OCCIPITAL JOINT

o Ligaments

o Movements

o Muscles help in movements

o Clinical aspects

ATLANTO-AXIAL JOINT

o Ligaments

o Movements

o Muscles help in movements

o Clinical aspects

BLOOD SUPPLY AND INNERVATIONS

INTIKHAB ALAM 58

ATLAS AND AXIS ANATOMY: The atlas is the topmost

vertebra and chief peculiarity of atlas is that it has no body, it is ring like and consist of anterior and posterior arch and two lateral masses.

Axis, the 2nd cervical vertebra has a concave under side and convex from side to side. The most distinctive characteristic of this bone is strong odontoidprocess, the dens.

DEFINITION The atlanto-occipital

joint (articulation between the atlas and the occipital bone) consists of a pair of condyloid joints.

The atlanto-occipital joints are synovial socket-type joints; the sockets are shallow in infancy and deepen with age.

LIGAMENTS The ligaments

connecting the bones are:

Two articular capsulesPosterior atlanto-

occipital membrane: extend from anterior arch of atlas to posterior margin of foramen magnum.

Anterior atlanto-occipital membrane: extend from anterior arch of atlas to anterior margin of foramen magnum.

SECONDARY LIGAMENTS The ligamenta flava

join laminae of adjacent vertebral arches.

The interspinousligaments expand to form the ligamentumnuchae which inserts along the posterior foramen magnum and external occipital condyle.

MOVEMENTSThe movements permitted in this joint are: flexion and extension in the Sagittal axis,

which give rise to the ordinary forward and backward nodding of the head.

slight lateral motion, lateral flexion to one or other side in the Frontal axis(titling of head).

It's where the nodding action of the head occurs.

MUSCLES HELP IN MOVEMENTo Flexion is produced

mainly by the action oflongi capitis ,rectus capitis anteriores andsternocleidomatoid(anterior fibers)

o Extension by the rectus capitis posterioremajor and minor, the obliquus capitissuperior, the semispinaliscapitis, splenius capiitis, longissimuscapitis, sternocleidomastoideus and upper fibers of the trapezius

MUSCLES HELP IN MOVEMENT The recti laterales

are concerned in the lateral movement, assisted by the trapezius, splenius capitis, semispinaliscapitis, and the sternocleidomastoideus of the same side, all acting together.

CLINICAL ASPECTS Headaches can arise from many different sources

including dysfunctional muscles, tears in the ligaments, misalignment of the vertebral bodies, injury to cervical facets and degenerative discs.

The joint bewteen the two structures is susceptible to traumatic injury and degeneration.

Excessive flexion could rupture the supraapinousligament.

Posterior atlanto-occipital membrane ossification cause migraine headaces due to compresion of artery.

SAJJAD AHMAD 29

DEFINITION:The joint formed b/w atlas

and axis in the upper part of the neck.

Synovial in nature. Atlanto-axial joint is of

complicated nature and consist of three distinct joints;

One is found between the dens of the axis and the anterior arch of the atlas.

Two are located between the lateral masses of the 1st cervical vertebra and the superior articular facets of the 2nd cervical vertebra.

LIGAMENTSThe following four ligaments

stabilize these joints:

Apical ligament: Connects the dens to the foramen magnum of the occipital bone.

Alar ligaments: Connect the dens to the lateral margins of the foramen magnum.

Cruciate ligament: Attaches the dens to the anterior arch of the atlas and the body of the axis to the foramen magnum of the occipital bone.

Tectorial membrane: Starts at the skull and becomes the posterior longitudinal ligament.

ARTICULAR CAPSULE The atlanto-axial articular

capsules are thick and loose, and connect the margins of the lateral masses of the atlas with those of the posterior articular surfaces of the axis.

Each is strengthened at its posterior and medial part by an accessory ligament.

MOVEMENTS:Lateral AAJ Movement:

It is a synovial joint which allows only gliding. The opposed articular surfaces of the atlas and axis are not reciprocally curved but are flat; when therefore, the upper facet glides forward on the lower it also descends; the fibers of the articular capsule are relaxed in a vertical direction, and will then permit movement in an antero-posterior direction.

Medial AAJ Movement:This joint allows the rotation of the atlas (and, with it, the skull) upon the axis i.e round the dens. The extent of rotation being limited by the alar ligaments.

INTERSTING FACT

Owl can rotate its head upto 270°.

This rotation compensate for their ooccularimmobility.

MUSCLES HELP IN MOVEMENTS: The principal muscles by

which these movements are produced are the Sternocleidomastoideusand Semispinalis capitis of one side, acting with the Longus capitis, Splenius, Longissimus capitis, Rectus capitis posterior major, and Obliqui capitissuperior and inferior of the other side.

MUSCLES ORIGIN INSERTION MOVEMENTS

obliquus capitisinferior

spinous process of the axis

transverse process of atlas

rotates the head to the same side

obliquus capitissuperior

transverseprocess of atlas

occipital bone above inferior nuchal line

extends the head, rotates the head to the same side

rectus capitisposterior major

spinous process of axis

inferior nuchalline

extends the head, rotate to same side

rectus capitisposterior minor

posterior tubercle of atlas

inferior nuchalline medially

extends the head

CLINICAL ASPECTS: Death by judicial hanging may

be due to the rupture of the transverse ligament of atlas or fracture of the dens of axis. As a result, the atlas is dislocated from the axis and compresses the spinal cord with fatal outcome.

Fractures of the dens make up about 40% of axis fractures.

When the transverse ligaments of the atlas ruptures the dens is set free resulting in atlanto-axial subluxation or incomplete dislocation of the medial-atlantoaxial joint.

CLINICAL ASPECTS:Pathological softening of the transverse and

adjacent ligaments usually resulting from disorders of connective tissue may also cause atlanto-axial subluxation.

Down syndrome exhibits laxity or agenesis of the ligament.

Dislocation owing to transverse ligament rupture or agenesis is more likely to cause spinal cord compression than that resulting from fracture of the dens.

CLINICAL ASPECTS: Sometimes inflammation in the craniovertebral area

may produce softening of the ligaments of the craniovertebral joints and cause dislocation of the atlanto-axial joints.

Alar ligaments are weaker than the transverse ligament of the atlas. Consequently combined flexion and rotation of the head may tear one or both alarligaments.

Although uncommon, atlanto-axial rotation may compress the C2 spinal nerve. This may be followed by prolonged severe headaches and excruciating cervico-occipital pain.

BLOOD SUPPLY AND INNERVATIONS

INNERVATION:• AAJ and AOJ nerves are supplied by the C1 and C2

nerves.

BLOOD SUPPLY: No blood supply, very

dependent certain

physiological factors

for health and restoration after injury however vertebral artery (important source of brain blood supply) passes through cervical vertebrae and it may supply these areas.

Different movements of head

POINTS TO BE NOTE Bursa: it is a fluid filled sac that helps reduce friction.

Ligamentum flavum at craniovertebral region has less elastic fibers, and more collagen fibers for providing greater stability and called posterior atlanto-axial and atlanto-occipital membranes.

Posterior Longitudinal Ligament become tectorialligament in the craniovertebral region much broader and stronger.

The Anterior Longitudinal Ligament becomes anterior atlanto-occipital membrane and the anterior atlantoaxial membrane in the craniovertebral region.

TIME OF YOUR ATTENTION

a)Crucite

b)Apical

c)Check

d)Alar

e)Both c and d

Which ligament prevents excessive rotation of these atlanto-axial joints?

How many atlanto-axial joints are there?

a)Two

b)Three

c)Four

What Is the superior continuation of posterior longitudenal ligament?

a)Ligamentum flavum

b)Accessory ligament

c)Membrana tectorai

d)Crucite ligamentum

e)Supraspinous ligament

What type of movement AAJ and AOJ do respectively?a)Flexion ,extention and rotation

b)Gliding and rotation

c)Rotation and flexion,extention

d)Tilting and rotation

Which one is rudimentary of notochord?a)Accessory ligament

b)Crucite ligament

c)Transverse ligament

d)Apical ligament

COMMON SITE OF FRACTURE OF AXIS?

a)Posterior arch

b)Anterior arch

c)Spinous process

d)Odontoid process