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Updated: Oct 13 2023

Odontoid Fracture

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  • Summary
    • Odontoid Fractures are relatively common fractures of the C2 (axis) dens that can be seen in low energy falls in elderly patients and high energy traumatic injuries in younger patients.
    • Diagnosis can be made with standard lateral and open-mouth odontoid radiographs. Some fractures may be difficult to visualize on Xrays and require a CT scan to diagnose. MRI is rarely indicated as these fractures are usually not associated with neurologic symptoms. 
    • Treatment may be nonoperative or operative depending on the Anderson and D'Alonzo type and risk factors for nonunion. Patient older than 80 have a high morbidity and mortality regardless of nonoperative or operative treatment. 
  • Epidemiology
    • Incidence
      • most common fracture of the axis
      • account for 10-15% of all cervical fractures
      • most common cervical spine fractures in the elderly
    • Demographics
      • occur in bimodal fashion in elderly and young patients
        • elderly
          • common, often missed, and caused by simple falls
          • associated with increased morbidity and mortality compared to younger patients with this injury
        • young patients
          • result from blunt trauma to head leading to cervical hyperflexion or hyperextension
        • children
          • rare and almost occur at site of  basilar synchondrosis 
  • Etiology
    • Pathophysiology
      • mechanism
        • displacement may be anterior (hyperflexion) or posterior (hyperextension)
          • anterior displacement
            • is associated with transverse ligament failure and atlanto-axial instability
          • posterior displacement
            • caused by direct impact from the anterior arch of atlas during hyperextension
      • biomechanics
        • a fracture through the base of the odontoid process severely compromises the stability of the upper cervical spine.
    • Associated conditions
      • Os odontoideum
        • etiology
          • previously thought to be due to failure of fusion at the base of the odontoid
          • evidence now suggests it may represent the residuals of an old traumatic process
        • imaging
          • appears like a type II odontoid fx on xray
        • treatment
          • observation
  • Anatomy
    • Osteology
      • axis has odontoid process (dens) and body
      • contains a transverse foramen which vertebral artery travels through
      • embryology
        • develops from five ossification centers
          • subdental (basilar) synchondrosis
            • is an initial cartilaginous junction between the dens and vertebral body that does not fuse until ~6 years of age
        • secondary ossification center 
          • appears at ~ age 3 and fuses to the dens at ~ age 12
    • Arthrology
      • C1-Dens
        • anterior dens articulates with anterior arch of C1
      • CI-C2 articulation
        • is a diarthrodial joint
      • C2-3 joint
        • participates in subaxial (C2-C7) cervical motion 
    • Ligaments
      • occipital-C1-C2 ligamentous stability
      • provided by the odontoid process and its supporting ligaments
        • transverse ligament
          • primary stabilizer of atlantoaxial joint
          • limits anterior translation of the atlas
        • apical ligaments
          • limit rotation of the upper cervical spine
        • alar ligaments
          • limit rotation of the upper cervical spine
    • Blood Supply
      • a vascular watershed exists between the apex and the base of the odontoid
        • apex
          • supplied by branches of internal carotid artery
        • base
          • supplied from branches of vertebral artery
        • the limited blood supply in this watershed area is thought to affect healing of type II odontoid fractures.
    • Kinematics
      • Normal Cervical Kinematics
      • Flexion/Extension
      • Rotation
      • Lateral Bend
      • Occipitocervical joint (OC)
      • 50
      • 4
      • 8
      • Atlantoaxial joint (C1-2)
      • 10
      • 50
      • 0
      • Subaxial Spine (C3-7)
      • 50
      • 50
      • 60
      • Total Motion (degrees)
      • 110
      • 100
      • 68
  • Classification
      • Anderson and D'Alonzo Classification
      • Type I
      • Oblique avulsion fx of tip of odontoid. Due to avulsion of alar ligament. Although rare,atlantooccipital instability should be ruled out with flexion and extension films .
      • Type II
      • Fracture through waist (high nonunion rate due to interruption of blood supply).
      • Type III
      • Fx extends into cancellous body of C2 and involves a variable portion of the C1-C2 joint.
      • Grauer Classification of Type II Odontoid fractures
      • Type IIA
      • Nondisplaced/minimally displaced with no comminution. Treatment is external immobilization
      • Type IIB
      • Displaced fracture with fracture line from anterosuperior to posteroinferior. Treatment is with anterior odontoid screw (if adequate bone density).
      • Type IIC
      • Fracture from anteroinferior to posterosuperior, or with significant comminution. Treatment is with posterior stabilization.
  • Presentation
    • Symptoms
      • neck pain
        • worse with motion, especially rotation
      • dysphagia
        • may be present when associated with a large retropharyngeal hematoma
    • Physical exam
      • neurologic deficits
        • very rare due to large cross-section area of spinal canal at this level
  • Imaging
    • Radiographs
      • required views
        • AP, lateral, open-mouth odontoid view of cervical spine
      • optional views
        • flexion-extension radiographs are important to diagnose occipitocervical instability in Type I fractures and Os odontoideum
          • instability defined as
            • atlanto-dens-interval (ADI)
              • > 10mm
            • space available for cord (SAC)
              • < 13mm 
      • findings
        • fx pattern best seen on open-mouth odontoid
    • CT
      • study of choice for fracture delineation and to assess stability of fracture pattern
    • CT angiogram
      • required to determine location of vertebral artery prior to posterior instrumentation procedures
    • MRI
      • indicated if neurologic symptoms present
  • Treatment
      • Treatment Overview Table
      • Type I
      • Collar
      • Type II (age < 40)
      • Halo Vest
      • Type II (40-80)
      • Surgery
      • Type II (> 80 years)
      • Collar
      • Type III
      • Collar
    • Nonoperative
      • observation alone
        • indications
          • Os odontoideum
            • assuming no neurologic symptoms or instability
      • hard cervical orthosis
        • indications
          • Type I
          • Type II in elderly who are not surgical candidates
            • union is unlikely, however a fibrous union should provide sufficient stability except in the case of major trauma
            • no evidence to support Halo over hard collar 
        • technique
          • typically worn for 6-12 weeks
      • halo immobilization
        • indications
          • Type II young patient with no risk factors for nonunion 
        • contraindications
          • elderly patients
            • do not tolerate halo (may lead to aspiration, pneumonia, and death)
        • technique
          • typically work for 6-12 weeks
    • Operative
      • posterior C1-C2 fusion
        • indications
          • Type II fractures with risk factors for nonunion
            • indicated in patient 50-80 
          • Type II/III fracture nonunions
          • Os odontoideum with neurologic deficits or instability
      • anterior odontoid screw
        • indications
          • Type II fractures with risk factors for nonunion AND
            • acceptable alignment and minimal displacement (reduction obtained) 
            • anterior oblique fracture pattern 
              • fracture line is perpendicular to screw trajectory
            • patient body habitus must allow proper screw trajectory
        • outcomes
          • associated with higher failure rates than posterior C1-2 fusion
      • transoral odontoidectomy
        • indications
          • severe posterior displacement of dens with spinal cord compression and neurologic deficits
          • rarely performed due to high complication rate
            • C1 laminectomy typically provides sufficient decompression of the spinal canal and is preferred
  • Techniques
    • Halo immobilization
      • complications
        • pin site infection
          • initial superficial pin infection can be treated with tightening and oral antibiotics 
    • C1-C2 posterior fusion
      • approach
        • posterior midline cervical approach
      • stabilization technique
        • sublaminar wiring techniques (Gallie or Brooks)
          • require postoperative halo immobilization and rarely used
        • posterior C1-C2 segmental fixation
          • C1 lateral mass screws
            • 10 degrees medial, 22 degrees cephalad
            • avoid perforation of anterior cortex of C1 lateral mass due to potential internal carotid arteryinjury 
          • C2 fixation options include
            • C2 laminar screws 
            • C2 pedicle screws
            • C2 pars scews (most common)
        • posterior C1-C2 transarticular screws construct
          • contraindicated in patients with an aberrant vertebral artery
      • outcomes
        • C1-C2 fusion will lead to 50% loss of neck motion
        • Higher fusion rate in elderly compared to anterior fusion
    • Anterior odontoid screw
      • approach
        • anterior approach to cervical spine
      • technique
        • single screw adequate
      • pros & cons
        • associated with higher failure rate than posterior C1-2 fusion
        • advantage is preservation of atlantoaxial motion
    • Transoral odontoidectomy
      • technique
        • usually combined with posterior stabilization procedure
  • Complications
    • Nonunion
      • overall incidence
        • 33% (up to as high as 88% in some studies)
      • risk factors
        • Type II fractures with 
          • posterior displacement ( > 2 mm) 
            • strongest predictor of nonunion
          • age > 40 years 
          • ≥ 5 mm displacement (>50% nonunion rate)
          • delay in treatment ( > 4 days)
          • angulations > 10°
          • smoker
    • Mortality
      • overall patient > 80 year of age do poorly with operative or nonoperative treatment 
        • especially with halo orthosis
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