Atlanto-Occipital Joints

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Atlanto-Occipital Joints

Concave oval superior facets of atlas

Convex/rounded occipital condyles

Horizontal plane

Lateral Atlanto-Axial Joints

Flat circular inferior facet of atlas

Flat circular superior facet of axis

Horizontal plane

Medial Atlanto-Axial Joints

Dens of axis

Articular fossa for dens on posterior surface of anterior arch of atlas

Frontal plane

Cervical Facets (C3-7)
Permits extensive rotation as well as flexion, extension and lateral flexion.

Flat, oval superior and inferior facets

Inferior face anterioinferior

Superior face posteriosuperior

Frontal at about 45° to horizontal

Thoracic Region (T1-12)
Permits rotation, flexion, extension, and lateral flexion but magnitude of motion is limited by the attachment to the ribs.

Flat, oval superior and inferior facets

Inferior face anterior

Superior face posterior

Frontal at about 60° to horizontal

Upper Lumbar (L1-2)
Restricted rotation but allows forward and lateral flexion and extension.

Oval and slightly concave superior facets

Oval and flat/slightly convex inferior facets

Inferior face laterally

Superior face medially

Sagittal at about 90° to horizontal
Has cephalad and caudal menisci that attach to joint capsule

Lower Lumbar (L4-5)

Oval and slightly concave superior facets

Oval and flat/slightly convex inferior facets

Inferior facets of L4 face anteriolaterally, L5 faces more anterior than lateral

Superior facets of L4-5 face posteriomedially

Diagnonal to sagittal and frontal at about 90° to horizontal
Has cephalad and caudal menisci that attach to joint capsule

*articular cartilage of facet joints is hyaline cartilage that is thick centrally and thin peripherally

*jt. Capsule is dense irregular connective tissue containing collagen and elastic fibers

*collagen limits facet joint movement- jt. Distraction, rotation and superor translation of inferior facets on the superior facet of the vertebra below as during forward flexion

*elastic fibers prevent the capsule and synovial membrane from being pinched between the opposing facets, allow for movement between the facets, and return the capsule it its starting position.

*menisci in lumbar region can become trapped between opposing articular surfaces producing a painful blockage of motion at the vertebral segment


*fibrocartilaginous joint between vertebral bodies

*Peripheral annulus fibrosis and central nucleus pulposus

*6-10 rings of Fibrocartilage

*collagen fibers in layers around nucleus are arranged loosely

*collagen fibers in outer layers are densely packed and run obliquely between vertebral bodies

*collagen fibers in the outermost 1-2 layers show a herringbone pattern which makes them strong in resisting tension

*peripheral-most fibers attach to the smooth edge (rim) of vertebral body with outermost fivers attaching to the periosteum and the anterior and posterior longitudinal ligaments

*other fibers attach to the hyaline cartilaginous end plate covering the rough articular surface of the vertebral body


*contains nucleus pulposus


*permits multidirectional movement

*shock absorbtion


*gelatinous mass of collagen fibers imbedded in a mucopolysccharide and water

*absorbs and retains large quantities of water

*exchange of nutrients between disk and vertebral bodies

*in cervical and thoracic regions, nucleus lies centrally within disk

*in lumbar region, nucleus lies in the posterior ½ of disk


*absorbtion and retention of water


*force transmission

*equalize unit stress in all directions to the annulus fibrosis

*permits a rocking type segmental movement between vertebral bodies

*movement between adjacent vertebrae is needed as is the ability of the AF and NP to expand

*NP expands at rest by drawing H2O & nutrients from blood vessels and lymphatics of the vertebral bodies

*as NP is loaded, the nutrient fluid is forced out into the AF and waste products out of the nucleus into the vertebral bodies

*flow of fluid inwardly during rest and outwardly during loading provides for nutritional needs of the disk


-synovial and fibrous articulation

-synovial articulation: auricular surface of sacrum (S1-3) and auricular surface of ilium lying anterior to PSIS and inferior to iliac tuberosity

-both auricular surfaces for the synovial portion have an irregular pattern of ridges and groves and both are covered with a thin layer of hyaline cartilage

Ligaments of the Spine

Anterior Atlanto-occipital membrane

Anterior arch of atlas with base of occiput

Continuous laterally with atlanto-occipital jt capsule

Posterior Atlanto-occipital membrane

Posterior arch of atlas with occiput

Continuous with lateral atlanto-occipital ligament

Anterior atlanto-axial membrane

Body of axis to anterior arch of atlas

Continuous with atlanto-axial jt capsule

Posterior atlanto-axial membrane

Posterior body of axis to posterior arch of atlas

Continuous with atlanto-axial jt capsule

Lateral atlanto-occipital ligament

Transverse process of atlas with occipital bone and strengthens atlanto-occipital jt

Tectorial membrane

Continuation of posterior longitudinal ligament connects posterior arch of axis to occipital bone covers cruciform, alar and apical ligaments

Cruciform ligament

Consists of transverse ligament of atlas, superior band and inferior band

Superior band attaches to occipital bone

Inferior band attaches to body of axis

Transverse ligament of atlas

Cups posterior surface of dens

attaches to posterior surface of anterior arch of atlas on each side of the medial atlanto-axial joint

Alar ligaments (paired)

Attach to sides and posterior surface of dens and run laterally with superior band attaching to occiput, middle band to lateral mass of atlas, inferior band to axis

Apical ligaments

Anterior to the superior band of cruciform ligament

Connects apex of dens to occiput

Anterior longitudinal ligament

Attaches to anterior rim of vertebral bodies and anterior aspect of IVD

Runs from sacrum to atlas

Becomes anterior atlanto-occipital membrane

Posterior longitudinal ligament

Attaches to posterior rim of vertebral bodies and posterior aspect of IVD

Anterior surface of spinal canal from sacrum to axis

Becomes tectorial membrane

Ligament flava

Paired segmental elastic ligaments on posterior aspect of spinal canal

Sacrum to axis

Connects lamina of adjacent vertebrae

Supraspinous ligament

Attaches to tips of spinous processes from C7

continuous with ligamentum nuchae to about L4

Replaced by erector spinae fascia

Interspinous ligaments

Inferior and superior aspects of adjacent SP from C7 to L5-S1

Ligamentum nuchae

Complex fibrous septum that runs along posterior midline of neck from C7 to occiput

Connects tips and superior and inferior aspects of cervical SP to the occiput

Intertransverse ligament

Connects TP of adjacent vertebrae

Iliolumbar ligament

Starts as muscle, ligament by 40

TP of L5(males)/L4-5 (females) to superior SIJ and ilium

Sacrotuberous ligament

Runs obliquely from posterior surface of PIIS and Posteriolateral aspect of lower sacrum and upper coccyx to the medial aspect of the Ischial tuberosity and Ischial ramus

Sacrospinous lgament

Runs obliquely from posteriolateral surface of lower sacrum and coccyx to Ischial spine

Interosseus SI ligament

Connects the iliac and sacral tuberosities at the fibrous SI jt

Short dorsal SI ligament

Run horizontally from dorsolateral aspect of the superior part of the sacral tuberosityto the dorsal aspect of the tuberosity of the ilium

Long dorsal SI ligament

Runs obliquely from the dorsolateral aspect of the inferior part of the sacral tuberosity and the dorsal surface of the sacrotuberous ligament to the PSIS

Ventral SI ligament

Runs horizontally from the ventrolateral margin of the sacrum to ventral aspect of the auricular surface of the ilium

Facet Joint Motion

-forward bending exposes some 40% of the facet joint area

-functional left sidebending causes more upward sliding of the right facet than does forward bending

-rotation to the right causes right facet distraction and left facet compression; left facet slide forward with vertebrae tilting into left side bending

-FWD BENDING: upward movement of inferior articular processes; slides up and forward

-BWD BENDING: downward movement of inferior articular processes; slides down and back contacting the lamina below

-LEFT ROTATION: gapping at left facet, right facet acts as a fulcrum

-SIDEBENDING/ROTATION: downslide of inferior articular facets on side to which cervical spine rotates; upslide on opposite side




Right Side Bend

Right Rotation


Occipital condyles Roll anteriorly

Glide posteriorly

Occipital condyles

Roll posteriorly

Glide anteriorly

Occipital condyles Roll right

Glide left

ROC moves slightly back

LOC moves slightly forward


Facets move forward

Facets move backward

Atlas slides right

RF moves back

LF moves forward


Facets slide up and forward

Facets slide down and back

RF slides down and back

LF slides up and forward

RF slides down and back

LF slides up and forward


Facets slide up

Facets slide down

RF slides down

LF slides up

RF distracts

LF compresses and acts as fulcrum


Facets slide up

Facets slide down

RF slides down

LF slides up

RF distracts

LF compresses and acts as fulcrum

Vertebrae Forward Flexion

Anterior tilting (rocking) of vertebral body over NP

Compression & bulging of anterior IVD (AF)

Tension on posterior IVD (AF)

NP deforms posteriorly

IV foramen increases

SP separate

Decreased compression on facet jt

Tension on supraspinous, interspinous, intertransverse, ligamentum flava, posterior longitudinal ligament

Slack on anterior longitudinal ligament

Vetebrae Backward Extension

Posterior tilting (rocking) of vertebral body of NP

Compression and bulging of the posterior IVD (AF)

Tension on anterior IVD (AF)

IV foramen decreases

SP converge

Increased compression on facet jt

Slack in supraspinous, interspinous, intertranverse, ligamentum flava, posterior longitudinal ligament

Tension on anterior longitudinal ligament

Vertebral Side Bending/Lateral Flexion
(in cervical spine, coupling occurs- when head and neck are bent right, SP go left.)

Lateral tilting of vertebral body over nucleus on side toward movement

Compression and bulging of IVD on side toward movement

Tension on IV on side opposite movement

Nucleus deforms to side opposite movement

IV foramen decreases on side of movement

IV foramen increases on side opposite movement

Increased compression on facet jt on side of movement

Decreased compression on facet jt on side opposite movement

Tension on intertransverse lig on side opposite movement

Slack on intertransverse lig on side of movement

Vertebrae Rotation

Increased compression on NP

Shear stress on AF

Increased compression on facet opposite to rotation

Decreased compression on facet joint on side of rotation

Tension on jt capsule on side of rotation

SI joint

Movement limited to 1-3 degrees

Movement mainly at anterioposterior direction

Rotation and translation occur

Nutation- movement of sacrum related to ilium as during fwd bending of trunk and squatting

Torsion- movement of ilium relative to sacrum as in lying supine and brining the knee to the chest

Loads on the Spine

Cervical Spine

*Loads at the AO jt are lowest in full extension and highest in full flexion

*Loads at C7-T1 are least when head is facing forward and chin is tucked

*Loads at C7-T1 are slightly greater when the head is in the correct posture, greater still when the head is extended and greatest at full flexion

Lumbar Spine

*Loads are least when lying supine

*Loads are low with relaxed standing, greater with supported sitting, and still greater with unsupported sitting

*Compression loads on the lumbar spine are greatest near the toe off stage in walking

*Loads increase on the lumbar spine as the velocity of walking increases
Muscle Actions

Forward trunk flexion from standing

Abs and ilipsoas move trunk forward while gravity pulls downward. Erector spinae eccentrically control downward movement. At 60 degrees of trunk flexion, pelvis rotates anteriorly at hips. Glute max and hamstrings eccentrically control anterior pelvic rotation.

Trunk extension from full flexion

Erector spinae very active at full flexion in stabilizing spine. During initial 30 degrees of extension, pelvis rotates posteriorly at hips. Glute max and hamstrings concentrically produce pelvic rotation. Last 60 degrees of extension is produced by concentric contraction of erector spinae.

Trunk side bending

QL, erector spinae and abs on side of movement initiate side bending to same side. Gravity pulls trunk further to same side. ES, QL on opposite side act eccentrically to control the rate and distance of gravity produced sidebending. Return to erect posture is produced by concentric activity of the ES and QL on the side opposite the gravity produced side bending.

Line of Gravity (LOG)

Atlanto-Occipital Jt

Lower C-Spine (C3-7)

Thoracic Spine

Lumbar Spine

Sacroiliac Joint

passes through dens of C2, bodies of T1, T12, S2
Maximal gravitational torque occurs at C5, T8, L3 where apex of each spinal curve are furthest from LOG

LOG: anterior
Moment: flexion

Passive forces: ligamentum nuchae

tectorial membrane

Active forces: posterior neck musckes

LOG: posterior
Moment: extension
Passive forces: anterior longitudinal ligament
Active forces: anterior scalene

Longus capitis

Longus colli

LOG: anterior
Moment: flexion

Passive forces: posterior longitudinal ligmament

Ligamentum flavum

Supraspinous ligmanet

Active forces: extensors

LOG: posterior
Moment: extension
Passive forces: anterior longitudinal ligament
Active forces: rectus abdominus



LOG: anterior
Moment: flexion

Passive forces: sacrospinous ligament

Sacrotuberous ligament

Sacroiliac ligament

Active forces: TA

Excessive Anterior Pelvic Tilt

Excessive Lumbar Lordosis

Excessive Thoracic Kyphosis

Excessive Cervical Lordosis

Increased compression of posterior bodies

Increased L5-S1 disk pressure

Increased lumbosacral angle

Potential slippage of L5 on S1

Ab stretched

Iliopsoas shortened

Increased compression of posterior bodies

Increased compression of facet jts

Increased disk pressire

Narrowing of IV foramen

Increased tension on anterior AF

ALL stretched

PLL, interspinous, lig. Flavum, lumber extensors shortened

Increased compression of anterior bodies

Increased disk pressure

Increased tension on facet capsule and posterior AF

Dorsal back and scap muscles stretched

ALL shortened

Anterior shoulder girdle and upper Abs shortened

Increased compression of posterior bodies

Increased compression of facet joints

Increased disc pressure

Narrowing of IV foramen

Increased tension on anterior AF

ALL stretched

Posterior spinal ligaments shorten

Posterior neck muscles shorten


  • Full Fibrocartilage articular disc that is connected to anterior joint capsule (attachment of superior head of lateral pterygoid)

  • Posterior disc attached to superior and inferior lamina

  • Superior lamina = elastic, stretches when disc moves anteriorly and recoils to move disc posteriorly

  • Inferior lamina= collagen, tightens when disc moves anteriorly to restrict the amount of anterior movement and slackens when disc moves posteriorly

Jaw Opening and Closing

Stage 1

11-25 mm between incisors

Anterior rotation of mandibular condyle in fossa and on disc

Disk does not move

Superior and inferior lamina are relaxed

Stage 2

40-50 mm between incisors

Anterior rotation and anterior translation of the mandibular condyle over articular eminence

Anterior translation of the articular disc with condyle as condyle moves over articular surface

Superior lamina stretches

Inferior lamina tightens

Initial Jaw Closing

40-50 mm to 11-25 mm

Posterior rotation and posterior translation of mandibular condyle back into mandibular fossa

Posterior translation of articular disc with condyle as condyle returns to fossa

Superior lamina recoils pulling disc posteriorly into fossa

Inferior lamina slackens as disc moves posterior into fossa

Lateral pterygoid contractions to control the rate of posterior disc movement

Terminal Jaw Closing

11-25 mm to full closure

Posterior rotation of mandibular condyle in fossa and on disc

Disc is within fossa

Superior and inferior lamina are relaxed

Tissue Mechanics
Load-Deformation Curve describes the relationship between the amount of stress/force and the amount of strain/deformation


-start of curve

-material is slack

-small amount of stress produces proportionally more strain


-material is tightening

-amount of stress is proportional to amount of strain

-when stress is released, material returns to original shape

-ability of a material to return to it’s non-deformed starting point define the elastic region of the material


-material is damaged

-degree of damage increases as the stress increases

-amount of strain/deformation increasing more relative to increase in stress

-necking point occurs in plastic region where the degree of material change is so extensive that the amount of deformation remans large with a decrease in stress

-material in plastic region is permanently deformed and will not return to it’s original position when the stress is removed

FAILURE is the point where the material completely breaks or ruptures
Stress/Strain curve for elastic material- as stress is applied, material deforms…when the stress is stopped, material returns to original size and shape….work lost during this process to deform the material is not completely recaptured once the forced are removed. Work lost is the area under the curves.
Young’s Modulus of Elasticity


Defines stiffness (resistance to deformation)

High Young’s Modulus= high stiffness

Low Young’s Modulus= low stiffness

Resilience is the mechanical work lost during deformation

R= work – change in work/work

Greater loss of work= less resilience

Less work lost= greater resilience

R=1 is perfectly resilient

1 2 3 4

1= good resilience and elastic

2= less resilient but still elastic

3= poor resilience, not elastic

4= not resilient, not elastic…good Damping
Damping is the opposite of resilience- styrofoam D=1-R

Toughness is resistance to mechanical failure

*amount of energy a material will absorb before it breaks

*toughness is not necessarily equal to strength

*strength is the magnitude of the force needed to break a material

Fragility is the opposite of toughness

*Fragile material absorbs little energy before it breaks

Brittleness describes materials that deform very little before failure

*brittleness is not necessarily related to strength (can be brittle- little formation but strong as in a drill bit)

Ductility is the ability of a material to deform progressively in tension without breaking

*old bone is more brittle than young bone

*young bone is more DUCTILE than old bone because young bone deforms farther when tension stress is applied than old bone.

-CT is made up predominantly of collagen fibers

-CT is formed from tropocollagen molecules (each has 3 polypeptide chains called alpha units that are wound about each other to form a triple helix)

-Tropocollagens are packed end to end and stacked side to side to form collagen fibril

-bound together by intra and inter chain bonds or cross-links between lysine and hydroxlysine

-cross links also bind fibrils together

-cross links contribute to high tensile strength, stability and stiffness of collagen so that collagen fibers with many cross-links are stiffer than collagen fibers with few cross-links

Type I collagen

Found in dermis of skin, bone tendon, ligament, Fibrocartilage, and fascia

Forms 90% of collagen in body and functions to resist tension and stretching

Type II collagen

Found in hyaline cartilage and elastic cartilage

Function is to resist pressure

Type III collagen

Found in CT of organs- liver, spleen, lungs, intestines

Also in blood vessels, nerves and muscles

Function is structural support

Important in wound closure

Type IV collagen

Found n basement membrane of epithelium

Function is to support tissue and act as a filter

Type V collagen

Found in basal lamina of smooth and skeletal muscle cells and Schwann and Glia cells

Functions as support system in these structures

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