CVJ EMBRYOLOGY, ANATOMY AND BIOMECHANICS

DR PRAVEEN K TRIPATHI

The term ‘cv junction’ refers to the occipital bone that surrounds the foramen magnum and the atlas and the axis vertebrae.

The C-V junction is a transition site between mobile cranium and relatively rigid spinal column. It is also the site of the medullo spinal junction.

Accounts for approximately 25% of the vertical height of the entire cervical spine

HISTORY Meckel , 1815 : manifestation of occipital Vertebrae Bell , 1830 : first described spontaneous Atlantoaxial dislocation 1886 – giacomini described the first case of congenital aad 1912Maurice Klippel and Andre Feil Chamberlain , 1937 : basilar invagination Carl List, in 1941, described the neurological syndromes

accompanying developmental anomalies of the occipital bone, the atlas, and the axis vertebrae

1960 – wadia-congenital aads Greenberg , 1968 : classified atlantoaxial Anomalies Atul Goel 2014 . Goel's Classification of Atlantoaxial ‘facetal’

dislocation.

EMBRYOLOGY ● Notochord forms early axial skeleton● During 4th week gestation, 42 somites

formedo 4 occipital, 8 cervical, 12 thoracic, 5

lumbar, 5 sacral, 8-10 coccygeal● Each somite differentiates

o outer dermatomeo inner myotomeo medial sclerotome - form vertebrae

around notocord 4 occipital sclerotomes

● 4th Occipital Sclerotome - Proatlas - important for CVJ development

CV JUNCTION EMBRYOLOGY Develops from the 4 occipital and upper 2

cervical somites. The mesoderm caudal to neural plate

condenses into four occipital somites, these are the precursors of occipital sclerotomes.

First Two - BasiocciputThird - Jugular tubercles

* Fourth occipital sclerotome

Proatlas

SCLEROTOMES IN FORMATION OF CVJ

**DO NOT RESEGMENT

FORMATION OF CVJ

Proatlas

Hypocentrum Centrum Neural arch

Anterior tubercle Apex of dens Ventral Dorsal of clivus & Apical ligament Rostral Caudal

First spinal sclerotome

Atlas vertebra is primarily formed from this sclerotome.

Sclerotome division

Hypocentrum Centrum Neural Arch

Anterior arch C1 Dens Inferior portion of (mid portion the posterior arch of the odontoidprocess and fused with axis)

Second spinal sclerotome

Develops into axis vertebra

Sclerotome division

Hypocentrum Centrum Neural Arch

Disappears Body of axis Facets & Posterior arch of axis

DEVELOPMENTAL PHASES OF C2

SURGICAL ANATOMY Constituents of CV junction

Osseous components and their articulations

Ligamento-muscular elementsNeuro-vascular structures

Characteristics of CV junctionMobility at the cost of stabilityConstantly changing structure and

kinematics –even in the post natal period

Vital neuro-vascular relations

Atlas* Named after the mythical giant who carried the earth on his shoulder.* Thin Anterior and posterior arches•Sturdy Lateral masses – made up of a column of superior and inferior articular facets placed in a vertical line•No body

Axis:Forms the axis of rotationDens is the divorced body of C1Bifid spinous processInferior facet more posterior than superior facet

External craniovertebral ligaments

Internal Craniovertebral Ligaments

LIGAMENTS OF CVJPOSTERIOR - POSTERIOR ATLANTOOCCIPITAL MEMBRANE: EXTENDS FROM OCCIPITAL BONE TO

POSTERIOR ARCH OF ATLAS. IT IS SHARP & THIN & IN DIRECT CONTACT WITH ANTERIOR CORTEX OF POSTERIOR ARCH OF ATLAS

ANTERIOR LIGAMENTS

Anterior LongitudinalLigament : Extending

from lower border of anterior arch of C1 to body of Axis

Anterior Atlanto-occipitalMembrane : Extends

from anterior edge of Foramen Magnum to anterior arch of C1

ANTERIOR LIGAMENTS

TECTORIAL MEMBRANE Cephalic extension

of PLL inserted into processus basilaris 1-2cm above basion

CRUCIATE LIGAMENT OCCIPITOTRANSVERSE

LIGAMENT: TO BASION INFERIOR LOGITUDINAL

BAND: TO AXIS BODY TRUE TRANSVERSE

LIGAMENT

TRUE TRANSVERSE LIGAMENT STRONG HORIZONTAL

PORTION MAINTAINS THE

POSITION OF DENS IN SAGITTAL & CRANIOCAUDAL DIRECTION

ARTICULATES WITH ODONTOID FACET

INSERTED LATERALLY IN BONY PROMINENCE IN INNER ASPECT OF CONDYLES

IT IS 8mm IN HEIGHT AND 2-3 MM THICK IN MIDLINE

ANTERIOR LIGAMENTS BARKOWS LIGAMENT-

FROM TIP OF DENS TO ANTEROLATERAL FM RIM

APICAL LIGAMENT- TIP OF DENS TO MIDDLE PART OF FM RIM

GRUBERS LIGAMENT- TRANSVERSE LIG TO TIP OF DENS

ALAR LIGAMENT- VERY STRONG

LIGAMENT 6 – 8 mm DENS TIP TO

LATERAL PART OF

RIM OF FM

BLOOD SUPPLYVERTEBRAL ARTERIES -

Anterior and Posterior ascending arteries.

CAROTID ARTERY : Anterior ascending artery.

Forms an apical arterial arcade in the region of alar ligament and sends perforators

VENOUS DRAINAGE : Periodontal venous plexus and suboccipital venous sinuses drain to pharyngovertebral veins

LYMPHATIC DRAINAGE : CV JUNCTION DRAINS TO RETROPHARYNGEAL LYMPH NODES & THEN TO THE UPPER DEEP CERVICAL CHAIN

RETROGRADE INFECTION OF CV JUNCTION FROM PHARYNX , SINUSES & RETROPHARYNGEAL AREAS : GRISEL’S SYNDROME

BIOMECHANICS OF CV JUNCTION

MOVEMENTS : FLEXION EXTENSION SLIDING

MOVEMENT LATERAL

FLEXION ROTATION

FLEXION & EXTENSION : JOINTS INVOLVED : OCCIPITOATLANTAL & ATLANTOAXIAL AVERAGE RANGE AT OCCIPITOATLANTAL JT. : 13 – 15 DEGREES ATLANTOAXIAL JT. : 10 DEGREES

FLEXION IS LIMITED BY : TECTORIAL MEMBRANE DENS BASION CONTACTEXTENSION LIMITED BY : STRETCHING OF TEC. MOPISTHION POST. ARCH OF ATLAS CONTACT

ANTERO-POSTERIOR TRANSLOCATION BETWEENDENS & ANT. RING OF ATLAS : ADULTS : 3mm YOUNG CHILDREN : 5mm ADULTS UPTO 5 mm : RUPTURE OF CRUCIATE LIG. > 5 mm : RUPTURE OF BOTH CRUCIATE & ALAR LIG.

ROTATION : JOINT INVOLVED : ATLANTOAXIAL

JOINT

MAXIMUM RANGE : 37 – 42 DEGREES

> ROTATION LEADS FACET JT. INTERLOCKING

ROTATION > 32 – 35 DEG. : ANGULATION OF CONTR. VERT. ARTERY

> 45 DEG. : IPSILATERAL VA OCCLUSION

LATERAL ROTATION : 90 DEG. JT. INVOLVED : ATLANTOAXIAL & LOWER C-SPINE

LATERAL FLEXION : SMALL AMPLITUDE 5 – 10 DEG.

SLIDING MOVEMENT :FORWARD OR BACKWARD MOVEMENT OF HEADWITHOUT FLEXION OR EXTENSION OF NECK

FORWARD SLIDE : AXIS INCLINES FORWARD POST. DISPLACEMENT OF AXIS ANT. ARCH OF ATLAS SLIDES UP ATLANTOODONTOID SPACE GAP OCCIPITOODONTOID SPACE GAP N : 3 – 6 mm DOUBLE IN FORWARD SLIDE

BACKWARD SLIDE :ANT. ARCH OF ATLAS SLIDES DOWN POST. ATLANTOOCCIPITAL SPACE

CLASSIFICATION OF CRANIOVERTEBRAL JUNCTION

ANOMALIES

Menezes classified CV junction anomalies into two broad categoriesCongenital (Primary)Developmental and Acquired (Secondary)

CV junction anomalies and AAD classifications overlap

Congenital (Primary)

Developmental and Acquired (Secondary)

Abnormalities of Foramen magnumDEFORMITIES OF FORAMEN MAGNUM N : AP DIAMETER – 30-40 mm STENOSIS : < 30 mm ENLARGEMENT : > 40 mm -MENINGIOMA - EPIDERMOID - CYSTIC MALFORMATION -ACM

AAD -DEFINITION AAD is not a disease per se , rather it’s a

manifestation of a spectrum of pathological states.

This is a condition in which the atlas(C1) slips over the axis(C2) in the antero-posterior direction resulting in neural structure compression between the two vertebrae.

A distance of >3mm in an adult & >4.5mm in a child between posterior surface of anterior Arch of C1 & anterior surface of dens is thought to be due to incompetence of Transverse Ligament with associated instability.

Greenberg’s Classification of AADI Incompetence of odontoid process

II Incompetence of Transverse Atlantal ligament

I Incompetence of odontoid process

A. Congenital 1. Type I Separate odontoid: OS odontoideum2. Type II Free apical segment: Ossiculum Terminale3. Type III Agenesis of odontoid base4. Type IV Agenesis of Apical segment5. Type V Agenesis of odontoid process totally

B. Traumatic1. Acute2. Chronic C. Infectious e.g TuberculosisD. Tumors1. Primary2. Metastatic

II Incompetence of Transverse Atlantal ligament

A. Congenital:1. Idiopathic2. Mongolism

B. Traumatic1. Acute - Rupture of TAL2. Chronic - Assimilation of atlas

- Block vertebrae C2 & C3

C. Hyperaemic1.Infection–Bacterial/viral(Grisel’s syndrome)/granulomatous2.Rheumatoid arthritis

Wadia proposed the following classification

Group I: AAD with* Occipitalization of atlas* Fusion of C2, C3 vertebrae* Odontoid process dislocated posteriorly

Group II: AAD with * No occipitalization of atlas* No Fusion of vertebrae* Odontoid process dislocated because of its maldevelopment

Group III: AAD with* No occipitalization* No fusion of vertebrae* Odontoid is normal in shape and size to body of the axis.

I & II are usually developmental and III is acquired

OTHER CLASSIFICATIONS Biomechanical

TranslatoryRotary

Radiological MobileFixed

ClinicalReducible Irreducible

Common Bony CV Junction Anomalies

BASILAR INVAGINATION: The term Basilar Invagination

was used by Chamberlain in 1939 .

This is a primary defect implying prolapse of the vertebral column into the skull at the base.

BASILAR INVAGINATION … Two types of Basilar invagination

A. Ventral: There is shortening of the basiocciput so that clivus is short & horizontally oriented thus displacing the plane of the FM in an upward direction compared with spinal column.

B.Paramesial : Condylar hypoplasia may be present so that clivus become dorsally displaced into posterior fossa but may be of normal length.

BI is commonly associated with an abnormal odontoid process invaginating into posterior fossa.

Axis becomes elongated and the true odontoid process is small.

There is abnormal clivus-odontoid articulation. The resultant abnormal clivus-canal angle produces an indentation on the pons, medulla or cervicomedullary junctionin a ventral manner.

Chiari Malformation is associated with BI in 25 – 30%cases.

PSEUDOBASILAR INVAGINATION

OCCIPITALIZATION OF POSTERIOR ARCH OF C1

HYPERTROPHY OF ODONTOID PROCESS

ASSOCIATED FEATURES :

ACM

BILATERAL AGENESIS OF VA

OS Odontoideum

Definition – An independent bone cranial to the axis, in the place of dens. It is not an isolated dens but exists apart from a small hypoplastic dens.

Two types : (Fielding & Griffin)A. Orthotopic variety: OS lies in the position of dens and moves with atlas and axis. B. Dystopic variety: OS lies near the inferior end of clivus & fuses with the occipital bone and moves in unison with clivus.

Congenital Os Odontoideum Traumatic Os Odontoideum 1. H/o Trauma - often present Always present2. Location - Usually between base of dens andusually between the base body of the axis (below superior and apical segment of the dens facet of axis )(above superior facet of axis)3. Line of separation - Always smooth Acutely irregular and not corticated and corticated 4. Associated congenital anomaly - Absent often present

PERSISTENT OSSICULUM TERMINALE

Failure of fusion of the terminal ossicle to remainder of the odontoid process

Fusion by 12 years of age Confused with a type 1 odontoid fracture

(avulsion of the terminal ossicle)Differentiation between traumatic or

congenital -difficultstable when isolatedodontoid process is usually normal in

height.

CLINICAL PRESENTATION OF CV JUNCTION ANOMALIES

The most interesting feature of the clinical presentation is the diversity.This is due to compression of the lower brainstem, cervical spinal cord, cranial nerves, cervical nerve roots, & vascular supply.

Presentation may be insidious, or as false localizing sign, infrequently a rapid neurological progression followed by death.

CLINICAL PRESENTATION…

The most common symptom is neck pain originating in suboccipital region with radiation to cranial vertex region -85%.

False localising signs: Usually motor monoparesis, paraparesis, & quadripresis.

CLINICAL FEATURES

GENERAL EXAM : Abnormal general physical

apperance.

KLIPPEL- FEIL SYNDROME :Triad of Low hairline,

short

neck and a webbed neck with limitation of neck

movements.

OTHER DYSPLASTIC FEATURES:

high arch palate

poly/syndactyly

pes cavus

scoliosis

sprengel shoulder,

MYELOPATHIC FEATURES

Motor deficits- legs more involved Cruciate paralysis Posterior tract symptoms- Lhermitte

sign Central cord syndrome Neck pain/ cough headacheCRANIAL NERVE SYMPTOMS Lower cranial nerve paresis Hearing loss(most common)-25% Hypoglossal paralysis (Klaus 1969)

BRAIN STEM/CEREBELLAR SIGNS

Sleep apnea and dysphagia Nystagmus Gait ataxiaVASCULAR SYMPTOMS Syncope Vertigo Episodic paresis Transient visual loss. Due to vertebro basilar insufficiency Present in 15 – 25% of cases.

Importants Points to remember

1. Short neck, low hairline, restricted neck movements are frequently seen in KF anomaly, Occipitalization, and basilar invagination

2. Transient Attacks of VB insufficiency are usually encountered in Pts. With A-A dislocation.

3. Several bony and soft tissue anomalies often co-exist

4. Neurological deficit is usually produced by A-A dislocation, Basilar Invagination, ACM and Syringomyelia / Syringobulbia

X-RAYS Conventional antero-posterior and lateral

views will reveal the presence and type of cranio-vertebral anomaly.

It will show whether the odontoid is present or absent and also the integrity of the rings of atlas and axis.

Block vertebrae and occipitalisation of atlas are also visualised.

The open mouth view shows hypoplastic odontoid, os odontoideum or ossiculum terminale with clarity.

LATERAL CRANIOMETRY determine basilar invagination, which

is an upward movement of the base of the skull in the region of the foramen magnum.

It is measured by the intracranial extension of the tip of the odontoid process.

Chamberlain's line (1939) is drawn from the posterior lip of the foramen magnum to the dorsal margin of the hard palate.

Intracranial projection of up to one third of the length of the odontoid is normal.

McGregor's line (1948) is drawn from the upper surface of the posterior edge of the hard palate to the most caudal point of the occipital curve of the skull.

The tip of the odontoid normally does not extend more than 4.5 mm above this line.

McRae's line (1953) defines the opening of the foramen magnum.

STRESS X-RAYS These are the lateral views of the cervical spine in

flexion and extension. These are absolutely essential to determine the

presence of atlanto-axial instability and cord compression.

The atlanto-dens interval (ADI) is the space between the anterior aspect of the dens and the posterior aspect of the anterior arch of atlas.

This is measured by the distance from the posterior aspect of the odontoid or axis to the nearest posterior structure. (Posterior ring of atlas or foramen magnum).

in patients with atlantooccipital fusion, those with less than 19mm of available space behind the odontoid or atlas were symptomatic.

CRANIOMETRY - LINESCHAMBERLAIN’S LINE MCRAE’S LINE

Posterior margin of hard palate to opisthion( )

Normal- tip of dens less than 5mm below this line

Abnormal- in basilar invagination

Line from basion to opisthion ( ) Normal – tip of dens below this

line Abnormal-in basilar invagination

CRANIOMETRY - LINESMCGREGOR’S LINE WACKENHEIM’S LINE

Posterior margin of hard palate to lowest part of occipital bone

Normal- tip of dens less than 7mm below this line

Abnormal- in basilar invagination

Line extrapolated along dorsal surface of clivus

Normal – dens should be tangential or anterior to this line

Abnormal-in basilar invagination

DIGASTRIC LINE BIMASTOID LINE

Line between incisurae mastoidae ( )

Normal- 10mm above atlanto-occipital joint

Line between tips of mastoid processes ( )

Normal – intersects atlanto-occipital joint

CRANIOMETRY - LINES

CRANIOMETRY - ANGLESWELCHER BASAL ANGLE CLIVUS CANAL ANGLE

Angle at junction of nasion-tuberculum and tuberculum-basion lines

Normal- 132-140 degree Abnormal->143 degree in

platybasia

Angle at junction of Wackenheim’s line and posterior vertebral body line

Normal – 150-180degree Abnormal-<150 degree in platybasia

ATLANTOOCCIPITAL JOINT AXIS ANGLE KLAUS INDEX

Angle formed at junction of lines along atlanto-occipital joints ( )

Normal -124-127 degree Obtuse in condyle hypoplasia

Distance between dens and tuberculum cruciate line ( )

Normal-40-41mm Basilar invagination-<30mm

CRANIOMETRY

Skull base flattening Primary and secondary Bow string deformity Increased basal angle Decreased clivus canal angle

( ) Association – basilar

invagination

32 year old gentleman with decreased clivus canal angle( ) , violation of Chamberlain’s line( , ) acute angulation, compression of cervicomedullary juncion ( )

PLATYBASIA

Abnormally high vertebral column

Prolapse into skull base Secondary- basilar impression Chamberlain’s line Mc Gregor’s line Digastric line

24 year old gentleman with violation of Chamberlain’s line( ) and digastric line( ), atlantoaxial dislocation(atlantodens interval-3.8mm)

BASILAR INVAGINATION

Anterior and posterior arch anomalies Total or partial aplasia Isolated anterior arch anomalies –rare Split atlas

CT axial section showing posterior atlas arch rachischisis

CT axial section showing partial anterior arch rachischisis( ) and os odontoideum( )Hypertrophic anterior arch( ); corticated margins

Jefferson’s fractureIrregular margins ; normal anterior arch

CONGENITAL ANOMALIES-ATLAS

OS ODONTOIDEUM OSSICULUM TERMINALE

Separate odontoid process Failure of fusion of base with body

of axis

Bergmann ossicle Failure of fusion of apical segment

with base of dens

CONGENITAL ANOMALIES-AXIS

T1W MRI sagittal section showing os odnotoideum(

CT sagittal section showing os odnotoideum( ) with ossiculum terminale( )

KLIPPEL FIEL SYNDROME CHIARI MALFORMATION

Complex entity causing cervicovertebral fusion

Associations- occipito-atlantoid fusion

Low lying tonsils Associations- basiocciput

hypoplasia, atlanto-occipital assimilation, platybasia

CONGENITAL SYNDROMES

16 year old lady with herniated tonsils( )Acute clivocanal angle( ),short clivus( ) and cervical cord compression

CT sagittal section showing violation of Chamberlain’s line ( ), atlantooccipital fusion( ), atlantodens interval of 3.9mm( ),fused C5-C8( )

Congenital Acquired Traumatic Atlantodens interval 3mm - adults 5mm - children

ATLANTOAXIAL DISLOCATION

20 year old man with type 2 dens fracture(irregular margins( ) and atlantoaxial dislocation( )

47 year old lady with rheumatoid arthritis with basilar impression, sclerosis of atlantoaxial joint( ) and atlantoaxial dislocation( )

18 year old lady with TB, retropharyngeal collection( ), lytic area in dens( ) and atlantoaxial dislocation( )

38 year old lady with increased atlantodens interval( )

SPONTANEOUS

INFECTIVE RHEUMATOID ARTHRITIS TRAUMA

Lines and angles used in radiologic diagnosis of C.V anomalies.

Parameter Normal range limits

A. PLATYBASIA

B. BASILAR INVAGINATION

C. ATLANTO-AXIAL DISLOCATION *

• Basal angle < 150 degree

• Boogard’s angle (Angle between the clivus line and McRae's line)< 136 degree

• Bull’s angle (Line drawn between the posterior and anterior arch of C1. Bull's angle is the angle between this line and the hard palate plane. < 13 degree

• Chamberlain’s line < one third of odontoid above this line• Mcgregor’s line < 5 mm• Mcrae line odontoid lies below this• Klaus height index > 35 mm• Atlanto-temporo > 22mm. mandibular index

• Atlanto-odontoid space upto 3 mm in adults upto 5 mm in children• EDFM > 19mm

* May be reducible, partially reducible or irreducible

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