Download An Overview of Ligamentous Biomechanics and

BLUNT TRAUMA
OF THE CRANIOCERVICAL JUNCTION:
An Overview of Ligamentous Biomechanics and
Injury Patterns
eEdE-241
John K. Fang, MD
Wilson Altmeyer, MD
Bundhit Tantiwonkosi, MD
Achint Singh, MD
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Disclosure Statement
• The authors have no financial interests to
disclose.
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Purpose
• Present relevant anatomy of the bony and
ligamentous structures of the craniocervical
junction
• Explain relevant biomechanics of the major
joints of the craniocervical junction
• Illustrate important injury patterns in
craniocervical juntion trauma in relation to its
anatomy and biomechanics
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Approach and Discussion
• Anatomy
– Major joints: atlanto-occipital and atlantoaxial
– Bones: occipital bone (Oc), atlas (C1), axis (C2)
– Ligaments
• Biomechanics
• Injury patterns
• Radiographic appearance
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Atlanto-occipital Joint
• Primary movements: flexion
and extension (27o, 25o)
• Primarily limited by bony
structures:
Bony Impingement
• Flexion: odontoid impinges
upon foramen magnum
• Extension: odontoid impinges
upon tectorial membrane
• Lateral: occipital condyles
• Occipital condyles articulate
with articular facets of the
atlas
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Atlantoaxial Joint
• Primary movement: axial
rotation
• Primarily limited by
ligaments
– Flexion: transverse
ligament
– Extension: tectorial
membrane
– Lateral: alar ligaments
• Rotation limited by bony
facets (40o)
– Vertebral artery occlusion
at > 45o
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Ligaments of the CCJ
• Significant ligaments
• Supporting ligaments
– Transverse (cruciate)
– Alar ligaments
–
–
–
–
–
–
–
–
David Fisher
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Cruciate (vertical)
Tectorial membrane
Transverse Occipital
Accessory atlantoaxial
Lateral atlantoaxial
Barkow
Apical
Posterior and anterior
atlantooccipital
– Nuchal
Transverse Ligament - Anatomy
• Horizontal component
of cruciform ligament
• Largest, strongest, and
thickest CCJ ligament
• Attaches to lateral
tubercles of the atlas
bilaterally
• Posterior to odontoid
process of C2.
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Transverse Ligament - Biomechanics
• Major stabilizer of the
atlantoaxial joint
• Primarily limits anterior
subluxation of atlas on
the axis
T
L
– Normal atlantodental
interval (ADI) = 3 mm
• Permits rotation of
atlantoaxial joint (47o)
• Tears occur centrally or at
bony attachments
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Transverse Ligament - Biomechanics
• Limits flexion at
atlantoaxial joint
• Limits impingement of
midbrain by dens during
flexion
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T
L
Alar ligaments - Anatomy
• Paired ligaments
stabilizing atlantoaxial
joint
• Attaches medial aspects
of occipital condyles to
posterolateral odontoid
• Forms angle (mean
154o) between
odontoid and skull base
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David Fisher
Alar ligaments - Biomechanics
• Primarily limits axial
rotation (45o) at
atlantoaxial junction
Lateral flexion
– Restricts rotation to
contralateral side
• Also limits lateral
flexion
• Excessive axial rotation
can result in vertebral
artery injury (>40-45o)
Axial rotation
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Tectorial Membrane - Anatomy
• Cranial continuation of
posterior longitudinal
ligament
• Posterior border of
supraodotoid space
• Not tightly adherent to
odontoid
• Attaches to clivus from
posterior body of C2
David Fisher
Nader S. Dahdaleh
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Tectorial Membrane - Biomechanics
• Controversial and inconsistent data on
anatomy and function
– Atlanto-occipital joint: restricts extension
– Atlantoaxial joint: restricts flexion/extension
• Limits compression of odontoid on spinal cord
• No significant contribution to lateral flexion or
axial rotation
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Transverse Occipital Ligament
• Accessory ligament
posterosuperior to alar
ligaments and odotoid
• Function similar to alar
ligaments in close
proximity
– May have direct
connection to alar
ligaments or odontoid
David Fisher
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Accessory Atlantoaxial Ligament
• Attaches from medial
aspect of the dorsal axis
to lateral mass of atlas
posterior to transverse
ligament.
• Paired ligaments
function similarly to alar
ligaments in restricting
axial rotation
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David Fisher
Lateral Atlantoaxial Ligament
• Lateral to anterior
atlantoaxial membrane
Occipital bone
– Attaches anterolateral
transverse process of
axis to jugular process of
occipital bone
Axis (transverse
process
Lateral Atlantoaxial
Ligament
• Minor role in limiting
lateral flexion and axial
rotation of the head
David Fisher
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Barkow Ligament
• Horizontal band
attaching anteromedial
occipital condyles.
– Anterior to alar
ligaments
• Assists transverse
ligament in limiting
extension at atlantooccipital joint
David Fisher
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Apical ligament
• Attaches top of
odontoid to basion
• Just posterior and
between the left and
right alar ligaments
• Questionable
importance to stability
of CCJ
Basion
Odondoid process
– May represent
rudimentary notochord
tissue
David Fisher
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Anterior Atlantoooccipital Ligament
• Thin membrane
between anterior arch
of atlas and anterior rim
of foramen magnum.
• Functions synergistically
with Barkow and
transverse ligaments
– Limits atlanto-occipital
extension
David Fisher
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Posterior Atlantoooccipital Ligament
• Thin membrane
between posterior arch
of atlas and posterior
rim of foramen
magnum
• Cephalad extension of
ligamentum flavun
• Current evidence that it
plays little role in CCJ
stability
David Fisher
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Nuchal ligament
• Cephalic extension of
supraspinous ligament
– Extends to inion of
occipital bone
• May restrict
hyperflexion of neck
• Possibly contributes to
proprioception
David Fisher
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Summary of Ligaments and Joints
Occiput – C2
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Alar
Tectorial
Apical
Nuchal
Atlanto-occipital
Atlantoaxial
– Anterior atlantooccipital ligament
– Posterior atlantooccipital ligament
– Lateral
atlantoaxial
– Transverse
– Accessory
atlantoaxial
– Atlantoaxial
joint capsule
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Craniocervical Instability
• Instability: Inability of spine to maintain
normal anatomic relationships and protect
spinal cord / vasculature
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Injury Patterns
• Axial loading
– Diving accidents
– Condylar fractures
• Combined hyperflexion
with axial rotation
– Rear end collision MVC
– Whiplash of slightly
rotated head causes
maximum rotation
– Damages alar ligaments
• Hyperextension
– Head on collision MVC
– Rapid deceleration of
head on steering wheel
– Hangman’s fractures
• Lateral flexion
– Side impact MVC
– Damages alar ligaments,
apical ligament
• Hyperflexion
– Transverse ligament
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Imaging Considerations
• Radiograph: evaluate specific distances
between structures of the CCJ
• CT: better visualizes fractures and dislocations
• MRI: best detects ligament damage, epidural
hematoma, and cord injury
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Tectorial Membrane Injury
• Defect within tectorial
membrane
• Spinal cord injury
reflects protective
function of tectorial
membrane from
traumatic flexion
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Tectorial Membrane Injury
• Epidural hematoma
– Indirect evidence of
underlying tectorial
membrane injury
– Indicates high energy
injury and other
underlying ligamentous
injury
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Transverse Ligament Injury
• Hyperflexion
• Increased atlanto-dens
interval (ADI) without
evidence of fracture
• ADI > 3.0 – 3.5 mm
• Failure of transverse
ligament to prevent
anterior subluxation of
atlas
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Transverse Ligament Injury
• Types of injury
– Intrasubstance tear
• Central
• Peripheral
– Avulsion of bony
tubercle at condyle
Joaquim, et al
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Transverse Ligament Injury
• Direct visualization of
transverse ligament
rupture
– Discontinuity of the T2
hypointense transverse
ligament
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Transverse Ligament Injury
• Intrasubstance
hyperintense T2 signal
• May represent partial
tear and indicate
instability
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Atlanto-occipital Dissociation
• “AOD”
• Classification:
displacement of occiput
with respect to atlas
– Type I: anterior
– Type II: longitudinal
– Type III: posterior
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Atlanto-occipital dissociation
• Basion-axis interval (BAI)
– Basion Anterior to dens: 12
mm (adults), 12 mm (child)
– Basion Posterior to dens: 4
mm, 0 mm (child)
– Sensitive for Type I and III
injuries
• Basion-dens interval (BDI)
– Sensitive for Type II injuries
– > 10 mm (adults)
– > 12 mm (child)
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Atlanto-occipital dissociation
• Type II AOD
• CT: Increased BasionDens Interval > 10 mm
• MRI: Hyperintense T2
signal in expected
region of apical and
atlanto-occipital
ligaments
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Atlanto-occipital dissociation
• Occipital condyle – C1
interval (CCI)
• “Condylar gap”
– On coronal plane
• Correlating for Type II
AOD injuries
– > 2.5 mm (adults)
– > 4 mm (children)
– Gross asymmetry
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Occipital Condyle Fractures
Anderson and Montesano
Classification
• Type I: Nondisplaced
comminuted fracture
Mechanics
• Associated with axial
loading
• Typically stable
• Type II: Extension of
basilar skull fracture to
condyle
• Rarely associated with
alar or ligamentous injury
– Typically stable
– Alar + transverse ligament
maintain stability
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Occipital Condyle Fractures
• Type III: Condylar
avulsion with medial
displacement
• Mechanic:
• Excessive or forced axial
rotation or lateral
bending
• Potentially unstable
• Associated with alar
ligament injury
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Occipital Condyle Fracture
• Type III occipital
condyle avulsion
fractures
• Can indicate underlying
alar ligament injury or
CCJ instability
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Occipital Condyle Fracture
• Type III avulsion
fracture of occipital
condyle
• Medial displacement of
fragment
• Increase clinical
suspicion of alar
ligament injury and CCJ
instability
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Occipital Condyle Fracture
• Combined comminuted
and avulsion fracture
with medial
displacement of
fragments
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Atlas Fractures: Jefferson Fracture
• Fractures of anterior
and posterior arches
• Suggests coexisting
transverse ligament
injury
• Axial loading
• Hyperextension
– Similar injury mechanics
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Atlas Fracture: Jefferson Fracture
• Can imply transverse ligament injury and CCJ
instability
Overhanging of lateral
masses of atlas over the axis
Increased distance between lateral masses
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Axis Fractures: Odontoid Fractures
• Type I: Tip of dens
• Type II: Base of dens
• Type III: Body of Axis
• Type II: most unstable
– Can result in spinal canal
compromise despite
intact transverse
ligament
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Axis Fractures: Odontoid Fractures
• Type II dens fracture
• Unstable
• Risk of anterior
translation of atlas on
axis
– Resultant spinal cord
compromise
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Axis Fractures: Hangman’s Fracture
• Traumatic
spondylolisthesis of axis
• Without other evidence
of ligamentous injury
– Hyperextension and
distraction injury
• Type I: nondisplaced, <
3mm distraction
• Type II: displaced > 3 mm,
angulated
• Type III: displaced,
angulated, with facet
dislocation
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– Low risk of neurological
compromise
– Conservative treatment
Joaquim, et al
Summary
Primary stabilizers of the CCJ
Radiograph and CT
• Transverse Ligament
– Visualize various bony
relationships implying
ligamentous injury
– Limits anterior
subluxation of atlas
• Alar Ligaments
– Limits axial rotation
MRI
– Visualize evidence of
direct ligamentous injury
• Several accessory
ligaments support the
above
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References
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Tubbs, RS, et al. Ligaments of the craniocervical junction. A review. J Neurosurg Spine 14: 697-709. 2011.
Radcliff KE, et al. In vitro biomechanics of the craniocervical junction- a sequential sectioning of its stabilizing structures. The
Spine Journal. 15: 1618-1628. 2015.
Steinmetz, MP, et al. Craniocervical Junction: Biomechanical Considerations. Neurosurgery. 66:A7-A12. 2010.
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occipital condyle–C1 interval. Journal of Neurosurgery: Spine. 24 (4). Apr 2016.
Pang, D. et al. Atlanto-occipital dislocation--part 2: The clinical use of (occipital) condyle-C1 interval, comparison with other
diagnostic methods, and the manifestation, management, and outcome of atlanto-occipital dislocation in children. Neurosurgery.
61(5): 995-1015. 2007.
Riascos, Roy, et al. Imaging of Atlanto-occipital and atlantoaxial Traumatic Injuries: What the Radiologist Needs to Know.
Radiographics. 35: 2121-2134. 2015.
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