Craniovertebral Jts, Prevertebral Region: Thurs, Oct. 5
Terms
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- Atlas:
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*ring of bone
1. 2 lateral masses bear weight of skull and have concave tubercles
2. articular facets (kidney) for reception of occipital condyle (A-O jt)
3. lateral masses attached to each other anteriorly and posteriorly by bony arches called anterior and posterior arches
**posterior arch has distinct groove for vertebral artery
4. transverse processes of atlas project further laterally than any other cervical vertebrae
*gives increased mechanical advantage to some muscles with attach to transverse processes
5. medial aspects of lateral masses have small tubercle on either side
*transverse ligament of atlas runs from one lateral mass to other
6. anterior arch has facet on its posterior aspect for articulation with dens of axis - Axis (C2):
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**strongest of all cervical vertebrae
1. major unique feature is dens, or odontoid process
a) articulates with anterior arch of atlas, and has facet posteriorly for transverse ligament which runs from side to side, just behind the dens
2. pair on either side of rather flat large facets (superior articular) which articulate with inferior articular processes of atlas (A-A jt)
3. articulation of dens with anterior arch of atlas froms median AA jt
4. axis has body and strong bifid spinous processes - Joints:
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1. AO jt:
a) ellipsoid synovial jt-each articular are forms segment of an ellipse
b) movement of one of these jts involves movement of the otehr
c) transverse diameter of ellipse is much longer than AP diameter
d) allows movement around 2 axes: i) around transverse axis for flexion and extension ("yes")/movement is between occipital condyle and superior articular facets of atlas; ii) A-P axis for lateral flexion (tilting head)
2. AA jts (3): 2 lateral, 1 median
a)lateral AA jts are gliding synovial; i) surfaces are flat and planar, ii) as you turn head, laterall AA get gliding motion, one side gliding forward and the other backward
b) median AA ft is classical case of pivot jt; i)little synovial cavities anterior and posterior to dens, lined with synovial membrane that allow rotation
b) shaking head "no", skull and atlas together rotate around dens, a stationary pivot - External craniocervial ligaments:
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AO jt:
1. has fibrous capsule which is loose, lined with synovial membrane
2. between 2 jts anteriorly, there is AO membrane, which stretches from anterior of atlas to anterior margin of foramen magnum
3. AO membrane is continuous with capsules of AO jts on either side
4. Posteriorly, posterior AO membrane, which stretches from posterior arch of atls to posterior margin of foramen magnum; i) pierced by vertebral artery and suboccipital nerve, ii) laterally, membrane bleds with capsule
AA:
1. lateral AA jt have rather loose capsule
2. between lateral AA jts can see upper continuation of ALL which attaches to anterior tubercle of atlas - Internal craniocervical ligaments:
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1. tectorial membrane: anterior to dura mater surround cervical spinal cord
a) upper continuation of PLL (runs on backs of vertebral bodies)
b) runs from axis to base of occipital bone
**important ligaments run deep to membrane:
i) transverse ligament of atlas, running side to side and covering back of dens; ii) superior and inferior longitudinal bands extend up and down from transverse (superior attaches to basilar part of occipital and inferior band to body of axis)
****these together make cruciate ligament
iii) alar ligaments: slightly deeper, run superiolaterally from lateral margin of dens to medial margin of occipital condyle; very strong; limit amount of rotation of head (contralateral checking)
**30% increase in rotation if cut
iv) apical ligament of dens, which extends from tip of dens to margin of forament magnum - **CC:
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1. Atlas:
a)Jefferson (burst) fracture:
i) compressive forces passed through occipital condyles into atlas
ii) lateral masses tend to be displaced laterally
iii) involves fracture of one or both of the bony arches of atlas
iv) sometimes, transverse ligament will rupture
v) dens may impinge on spinal cord
2. Axis
a) Hangman's fracture:
i) hyperextension of head on neck
ii) fractures pars interarticularis of axis (between superior and inferior articular processes)
b) dens can be fractured, usually at its base, which results in avascular necrosis
**about 40% of axial fractures involve dens
3. Transverse Ligament: can be ruptured
i) atlas becomes displaced anteriorly
ii) posterior arch of atlas traps spinal cord between it and dens
iii) some leeway for anterior displacement b/c of ~1/3 of diameter of ring of atlas is occupied by dens, 1/3 by spinal cord, and 1/3 by soft connective tissue, meninges, and fluids
**Steele's Rule of 1/3s: can get displacement of atlas of up to 1/3 of diameter of ring and may be relatively asymptomatic - Prevertebral Region: 4 muscles
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1. longus coli: originates from upper thoracic and lower cervical vertebrae; inserts into cervial vertebrae more superiorly (highest extent attaches to anterior tubercle of atlas)
Action: bilaterally, flexes neck (SCM and scalenes assist)
2. longus capitis: originates from cervical vertebrae and inserts in to basilar part of occipital bone
3. rectus capitis anterior: runs from lateral mass of atlas to basilar part of occipital
4. rectus capitis lateralis: runs from transverse process of atlas to jugular process of occipital
**all innervated by twigs ventral rami of cervical nerves - Lateral vertebral muscles: Scalenes
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1. anterior: inserts into scalene tubercle of rib 1
2. middle: inserts into upper surface of rib 1
3. posterior: inserts onto outer margin of rib 2
Actions: bilaterally, can elevate first 2 rib if neck is fixed ; unilaterally, lateral flexion of neck
**innervated same as prevertebrals - Movements at AO/AA jts:
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1. Flexion: longus capitis and rectus capitis anterior
*SCM and infra-, supra- hyoid muscles can pull down on hyoid and mandible and indirectly cause flexion
2. Extension: suboccipital muscles (rectus capitis posterior major and minor, superior oblique, trapezius)
3. Tilting: rectus capitis lateralis
AA jt:
1. turning: contracting SCM contralaterally
2. lateral rotation: suboccipital and some deep muscle in back of neck cause rotation to same side (RCP major, splenius capitis, longissimus capitis)
*transverse process of atlas extends so far laterally gives mechanical advantage for inferior oblique - Relationships with scalene muscles:
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1. to anterior scalene:
a) phrenic nerve descends anterior
b) suprascapular and transverse cervical arteries run laterally across, and clamp phrenic
c)inferior thyroid artery runs in front of muscle as it arches medially to thyroid gland
d) ascending cervical branch, off inferior thyroid, lies anteriorly
e) subclavian vein lies just in front of insertion
f) posteriorly, 2nd part of subclavian artery and brachial plexus, run between anterior and middle scalenes
Interscalene triangle: anterior and middle scalenes and 1st rib
**CC: cervical rib reduces size of triangle (in 0.5-1%) and can cause lower trunk of brachial plexus to be elevated and compressed as well as subclavian artery - Deep cervical fascia and associated fascial spaces:
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1. Investing layer: encloses SCM and trapezius/single layer in front of neck on side; forms roof of posterior triangle
2. Prevertebral fascia: covers prevertebral muscles and extends laterally and covers scalene muscle, extends posteriorly and forms a complete tubular investment for prevertebral muscles and those in back of neck
3. Visceral fascia: surrounds cervical viscera (trachea, esophagus, thyroid gland); 2 components: a) pretracheal-forms sheath for thyroid gland, b) buccopharyngeal layer-covers buccinator and pharyngeal muscles, covers back of esophagus
4. Retropharyngeal space: behind pharynx or esophagus, bound anteriorly by buccopharyngeal fascia, posteriorly lies in front of prevertebral muscles and fascia
a) filled with loose areolar tissue which allows pharynx and esophagus to expand when swallow
b) carotid sheath on either side
c) extends from base of skull all way down behind heart, in posterior mediastinum
5. carotid sheath: made up of investing, prevertebral and visceral layers
a) surrounds CCA, IJV, and vagus
6. Lateral pharyngeal space: fat filled space wiht 2 muscles--styloglossus and stylopharyngeus
a) lies just medial to pterygoid muscles and parotid gland
b) continuous with retropharyngeal space
**CC: common site for thing to get infected are palatine tonsils, base of tongus, teeth - Neurovascular relationships:
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1. CNIX: seen better with pharynx, wraps around stylopharyngeus
2. CNX: descends in carotid sheath between IJV laterally and CCA or ICA medially
3. CNXI: runs inferolaterally; enters deep side of SCM
4. CNXII: descend and starts to loop forward b/c goes to tongue muscles; closely boudn to vagus; crosses both carotid arteries
5. sympathetic trunk: lies just posterior to carotid sheath - Cervical part of sympathetic trunk:
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*3-4 ganglia: superoir, middle, and inferior cervical ganglia
1. inferior usually fused (80%) with 1st thoracic to form cervicothoracic, or stellate, ganglion
2. sometimes 4th ganglion, vertebral ganglion, between middle and stellate ganglia
3. cervical part of sympathetic trunk consists primarily of ascending pre-synaptic sympathetics which have entered trunk in upper thoracic region
4. pre-synaptic cell bodies lie in lateral horn of upper thoracic, then enter trunk, ascend and synapse in one of 4 ganglia
5. post-synaptic fibers will go supply structures in head and neck
6. sympathetic fibers travel up along arteries and branches and leave plexus to innervate smooth muscle and glands in head and neck (including blood vessels) - 2 ways for post-synaptic fibers to supply head and neck:
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1. via gray rami communicantes that connect cervical ganglia with cervical spinal nerves
a) 3-4 cervical ganglia but 8 cervical nerves; every spinal nerve has gray ramus attached
b) superior cervical ganglion sends gray rami to upper 4 cervical nerves
c) middle usually supplies C5-C6
d) inferior supplies C7-C8
e) fusion of gangla during development results in 3-4; accounts for variability
2. postsynaptic fibers travel along blood vessels:
a) major nerve coming off superior cervical ganglion, internal carotid nerve-travels along ICA, forming plexus around it, up into skull
b) external carotid nerve and plexus - Horner's Syndrome:
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**lesions in sympathetic trunk
1. ptosis and miosis: involve internal carotid plexus by way of dilator pupillae and superior tarsal muscles
2) vasodilation and anhidrosis involves ECA and plexus