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Summary
  • Occipital condyle fractures are traumatic injuries that involve articulation between the base of the skull and the cervical spine. 
  • Diagnosis of the fracture is best made with a CT scan. An MRI and/or flexion-extension radiographs are used to evaluate for associated occipitocervical instability.
  • Most fractures are treated with immobilization with a cervical orthosis. Occipitocervical fusion is indicated in the rare cases where occipitocervical instability is present.
Science
  • Terminology
    • occipital condyle fractures represent a subset of basilar skull fractures.
  • Epidemiology
    • incidence
      • relatively uncommon.
      • approximately 1-3% of population with blunt craniocervical trauma.
      • often missed due to low diagnosis sensitivity of plain radiographs.   
        • reported incidence is increasing due to increased utilization of CT scans.
  • Pathophysiology
    • mechanism 
      • high energy, non-penetrating, trauma to the head/neck
        • motor vehicle accident
        • fall from height.
      • low energy trauma to head and neck
        • occasionally seen in ground level falls in elderly due to direct blow to the skull.
    • pathoanatomy
      • fracture patterns are dependent on the directional forces applied to the craniocervical junction at the time of the injury including
        • axial compression
        • horizontal sheer due to a direct blow on the skull
        • rotation
        • lateral bending
  • Associated injuries
    • orthopaedic manifestations
      • cervical spinal cord injuries (31%)
        • neurological deficits may be acute (63% of cases) or delayed (37% of cases)
      • cervical fractures
      • vertebral artery injury
      • polytrauma
    • medical manifestations
      • intracranial bleeding
      • brainstem and vascular lesions
      • elevated ICP
  • Prognosis
    • high mortality rate (11%) due to associated injuries.
      • rate has decreased due to improvement in first responder cervical spine precautions.
Anatomy
  • Osteology
    • occipital condyle morphology
      • occipital condyles are paired oval prominences of the occipital bone that form the lateral aspects of the foramen magnum.
    • occipitoatlantal joint (occiput/C1)
      • articulation
        • each occiput articulates with a shallow dish-like joint on the superior aspect of the lateral mass of C1.
        • joint morphology allows for large range of flexion and extension of craniocervical junction.
      • ligamentous stability
        • provide by a combination of
          • occipitoatlantal joint joint capsule 
          • alar ligaments (dens to each occipital condyle)
  • Ligaments
    • intrinsic ligaments are located within the spinal canal, provide most of the ligamentous stability. They include
      • transverse ligament  
        • connects the posterior odontoid to the anterior atlas arch, inserting laterally on bony tubercles. 
        • primary stabilizer of atlantoaxial junction.
      • paired alar ligaments  
        • connect the odontoid to the occipital condyles.
        • relatively strong and contributes to occipitocervical stability.
      • apical ligament  
        • runs vertically between the odontoid and foramen magnum.
        • relatively weak midline structure.
      • tectorial membrane 
        • connects the posterior body of the axis to the anterior foramen magnum and is the cephalad continuation of the PLL.
  • Vascular system
    • vertebral artery
      • occipital condyles are in proximity to vertebral arteries.
  • Nervous system
    • occipital condyles in close proximity to
      • medulla oblongata
      • spinal cord
      • lower cranial nerves (CN IX - CN XII)
      • C2 nerve root
  • Biomechanics
    • occipitoatlantoaxial complex (craniocervical junction)
      • function
        • an anatomic complex that provides stability and function of craniocervical junction (occiput to C2).
      • includes 6 articulations
        • occipitoatlantal joints
        • 2 paired lateral C1-C2 facets/joints
        • 1 dens-anterior arch of C1 articulation
        • 1 posterior midline atlantoaxial joints
      • three ligamentous structure connect C2 directly to base of skull (thereby skipping C1)
        • apical ligament
        • alar ligament
        • tectorial membrane
Classification
 
 Anderson and Montesano Classification of Occipital Condyle Fractures
Type I 3%  • Impaction-type fracture with comminution of the occipital condyle
 • Due to compression between the occipitoatlantal joint
 • Stable injury due to minimal fragment displacement into the foremen magnum
   
Type II 22%  • Basilar skull fracture that extends into one- or both occipital condyles
 • Due to a direct blow to skull and a sheer force to the occipitoatlantal joint
 • Stable injury as the alar ligament and tectorial membrane are usually preserved
  
Type III 75%  • Avulsion fracture of condyle in region of the alar ligament attachment (suspect underlying occipitocervical dissociation)
 • Due to forced rotation with combined lateral bending.
 • Has the potential to be unstable due to craniocervical disruption
  
 
Presentation
  • History
    • clinical presentation is highly variable
    • often a history of high energy trauma with associated injury (head injury, vertebral artery injury, spinal cord injury)
  • Symptoms
    • high cervical pain
    • neck stiffness
    • double vision
    • upper and lower extremity weakness
  • Physical examination
    • inspection
      • look for trauma to skull (e.g, skull laceration)
    • ROM
      • remove collar and evaluate limited motion
        • limited cervical ROM may elicit pain
    • neurologic
      • extremity exam
      • rectal exam
      • lower cranial nerve exam
        • deficits most commonly affect CN IX, X, and XI
Imaging
  • Radiographs
    • recommended views
      • AP, lateral, open-mouth AP view
    • alternative views
      • flexion and extension views
    • findings
      • diagnosis rarely made on plain radiographs due to superimposition of structures (maxilla, occiput) blocking view of occipital condyles
      • open-mouth AP view may depict occipital condyle injuries
    • measurements
      • Powers ratio
        • used to diagnosis occipitocervical dislocation
        • technique
        •  Powers ratio = C-D/A-B  
          • C-D: distance from basion to posterior arch
          • A-B: distance from anterior arch to opisthion
        • significance
          • ratio of ~ 1 is normal
          • if > 1.0 concern for anterior dislocation
          • if ratio < 1.0 raises concern for posterior dislocation, odontoid fractures, or ring of atlas fractures
      • O-C2 angle
        • technique
          • angle between McGregor line and C2
        • significance
          • needs to be established prior to OC fusion to prevent postoperative dysphagia by causing a significant change relative to the preoperative O-C2 angle
      • C2 to T1 lordotic alignment
  • CT 
    • indications
      • method of choice
      • routine CT imaging in high-energy trauma patients
      • clinical criteria:
        • altered consciousness
        • occipital pain and tenderness
        • impaired CCJ motion
        • lower cranial nerve paresis
        • motor paresis
    • views
      • must include cranial-cervical junction with thin-section technique
    • findings
      • occiput fracture
        • may see migration of fragment into spinal canal
      • joint diastasis (2mm or less is considered normal)
  • CT angiogram
    • indications
      • concern for Vertebral Artery injury
      • surgical planning to identify location of vertebral artery
  • MRI
    • indications
      • evaluation of soft-tissue craniocervical trauma
      • spinal cord or brain stem ischemia
    • views
      • MR angiogram may be considered with suspected vascular injury
    • findings
      • edema or fluid collection in the occipitoatlantal joint representing rupture of the occipitoatlantal joint capsule
      • edema or fluid collection consistent with avulsion injury of alar ligament from dens or occiput
Differential
  • Key differential
    • occipitocervical instability
    • atlas fractures
    • odontoid fracture
Treatment
  • Nonoperative
    • immobilization with cervical orthosis
      • incidence
        • indicated in vast majority of low energy fractures
      • indications
        • Type 1 and 2
        • Type 3 without overt instability
      • modalities
        • semi-rigid or rigid cervical collar
        • usually worn for 6 weeks
  • Operative
    • occipitocervical fusion
      • incidence
        • very rarely indicated
      • indications
        • Type 3 with overt instability
        • neural compression from displaced fracture fragment
        • associated occipital-atlantal or atlanto-axial injuries
Techniques
  • Occipitocervical fusion
    • approach
      • posterior midline incision with patient in prone position
      • Mayfield retractor used to obtain proper craniocervical alignment
        • establish preoperative O-C2 angle with lateral fluoroscopy prior to draping
    • deep dissection
      • if performing C1 lateral mass screw fixation work within safe zone and do not dissect above the posterior arch of C1 more than 1 cm lateral to midline to avoid injury to vertebral artery
    • instrumentation
      • length
        • posterior segmental instrumented fusion is usually performed from the occiput to C3
      • occipital
        • occipital plates usually allow for 3 or 4 total screws with adjustable rod holders
        • occipital screws
          • usually unicortical to avoid injury to venous sinus
            • major dural venous sinuses are located just below the external occipital protuberance and are at risk of penetrative injury
            • some institutions prefer bicortical screws but they come at increase risk
          • occipital screw safe zone
            • the safe zone for occipital screws is located within an area measuring 2 cm lateral and 1 cm inferior to the external occipital protuberance along the superior nuchal line  
      • C1 lateral mass screws
        •  often skipped due to angle at base of skull making it more difficult to place a rod
        • may choose a unilateral screw to provide some rotational stability to C1 ring
      • C2 fixation
        • pars, pedicle screws, transarticular, or translaminar screws all options
      • C3 fixation
        • standard lateral mass screws aimed cephalad and lateral to avoid vertebral artery
    • arthrodesis
      • perform decortication of occiput, posterior arch of C1, and lamina of C2
      • may require autogeneous bone grafting or bone allograft
    • postoperative immobilization
      • patients frequently immobilized in halo or hard cervical orthosis for 6-12 weeks to obtain fusion
Complications
  • Nonoperative
    • neck pain & stiffness
  • Operative
    • intracranial venous sinus injury (occipital screws)
    • vertebral artery injury (C1 lateral mass screws)
    • adjacent segment disease
    • neck pain & stiffness

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