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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 Home Disclosure Statement • The authors have no financial interests to disclose. Home 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 Home Approach and Discussion • Anatomy – Major joints: atlanto-occipital and atlantoaxial – Bones: occipital bone (Oc), atlas (C1), axis (C2) – Ligaments • Biomechanics • Injury patterns • Radiographic appearance Home 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 Home 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 Home Ligaments of the CCJ • Significant ligaments • Supporting ligaments – Transverse (cruciate) – Alar ligaments – – – – – – – – David Fisher Home 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. Home 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 Home Transverse Ligament - Biomechanics • Limits flexion at atlantoaxial joint • Limits impingement of midbrain by dens during flexion Home 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 Home 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 Home 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 Home 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 Home 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 Home 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 Home 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 Home Barkow Ligament • Horizontal band attaching anteromedial occipital condyles. – Anterior to alar ligaments • Assists transverse ligament in limiting extension at atlantooccipital joint David Fisher Home 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 Home 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 Home 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 Home Nuchal ligament • Cephalic extension of supraspinous ligament – Extends to inion of occipital bone • May restrict hyperflexion of neck • Possibly contributes to proprioception David Fisher Home Summary of Ligaments and Joints Occiput – C2 – – – – Alar Tectorial Apical Nuchal Atlanto-occipital Atlantoaxial – Anterior atlantooccipital ligament – Posterior atlantooccipital ligament – Lateral atlantoaxial – Transverse – Accessory atlantoaxial – Atlantoaxial joint capsule Home Craniocervical Instability • Instability: Inability of spine to maintain normal anatomic relationships and protect spinal cord / vasculature Home 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 Home 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 Home Tectorial Membrane Injury • Defect within tectorial membrane • Spinal cord injury reflects protective function of tectorial membrane from traumatic flexion Home Tectorial Membrane Injury • Epidural hematoma – Indirect evidence of underlying tectorial membrane injury – Indicates high energy injury and other underlying ligamentous injury Home 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 Home Transverse Ligament Injury • Types of injury – Intrasubstance tear • Central • Peripheral – Avulsion of bony tubercle at condyle Joaquim, et al Home Transverse Ligament Injury • Direct visualization of transverse ligament rupture – Discontinuity of the T2 hypointense transverse ligament Home Transverse Ligament Injury • Intrasubstance hyperintense T2 signal • May represent partial tear and indicate instability Home Atlanto-occipital Dissociation • “AOD” • Classification: displacement of occiput with respect to atlas – Type I: anterior – Type II: longitudinal – Type III: posterior Home 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) Home 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 Home 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 Home 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 Home 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 Home Occipital Condyle Fracture • Type III occipital condyle avulsion fractures • Can indicate underlying alar ligament injury or CCJ instability Home Occipital Condyle Fracture • Type III avulsion fracture of occipital condyle • Medial displacement of fragment • Increase clinical suspicion of alar ligament injury and CCJ instability Home Occipital Condyle Fracture • Combined comminuted and avulsion fracture with medial displacement of fragments Home Atlas Fractures: Jefferson Fracture • Fractures of anterior and posterior arches • Suggests coexisting transverse ligament injury • Axial loading • Hyperextension – Similar injury mechanics Home 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 Home 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 Home Axis Fractures: Odontoid Fractures • Type II dens fracture • Unstable • Risk of anterior translation of atlas on axis – Resultant spinal cord compromise Home 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 Home – 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 Home References • • • • • • • • • • • • • • • 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. Martin, MD, et al. Anatomic and Biomechanical Considerations of the Craniocervical Junction. Neurosurgery. 66:A2-A6. 2010. Jeffrey G. Clark, Kalil G. Abdullah, Thomas E. Mroz and Michael P. Steinmetz (2011). Biomechanics of the Craniovertebral Junction, Biomechanics in Applications, Dr Vaclav Klika (Ed.), ISBN: 978-953-307-969-1, InTech, Available from: http://www.intechopen.com/books/biomechanics-in-applications/biomechanics-of-thecraniovertebral-junction. Lopez, AJ, et al. Anatomy and Biomechanics of the Craniocervical Junction. Neurosurgical Focus. 38 (4): E2. 2015. Siegmund, GP, et al. 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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. Home
