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http://upload.orthobullets.com/topic/2000/images/type_a_separation.jpg
http://upload.orthobullets.com/topic/2000/images/kotani.jpg
http://upload.orthobullets.com/topic/2000/images/type_b_comminution.jpg
http://upload.orthobullets.com/topic/2000/images/type_c_split.jpg
http://upload.orthobullets.com/topic/2000/images/pedicle_screw_system.jpg
http://upload.orthobullets.com/topic/2000/images/lateral_mass_plating.jpg
Introduction
  • Fracture separations of the lateral mass-facet are uncommon injuries characterized by
    • high degree of instability
    • neurological deficit
    • affect 2 levels (2 adjacent motion segments) 
      • because of involvement of the superior facet and inferior facet on either side of the fractured articular mass
  • Epidemiology
    • demographics
      • male : female ratio = 2:1
      • mean age 35 yrs (20-70yrs)
    • location
      • C6 > C5 > C7 > C4 > C3
  • Pathophysiology
    • mechanism of injury
      • traffic accident, falls, heavy object landing on head
      • hyperextension, lateral compression and rotation of the cervical spine
  • Associated conditions
    • anterior translation (listhesis)
      • fractured vertebrae (77%)
      • superior adjacent vertebrae (24%)
      • inferior adjacent vertebrae (10%)
    • coronal translation (33%)
    • vertebral body collapse (33%)
      • lower in Type A Separation fracture subtypes
Classification
  • Kotani Classification
Kotani Classification 
Fracture Type Fracture Description 
Rates of Anterior Translation (same level)   Rates of Anterior Translation (adjacent level)    
Type A - Separation fracture 2 fracture lines of unilateral lamina and pedicle 91% 20%
Type B - Comminution type Multiple fracture lines with lateral wedging in coronal plane
- 50%  
Type C - Split type Vertical fracture line in the coronal plane, with invagination of the superior articular process of the caudal vertebra 80% 0%
Type D - Traumatic spondylolysis  Bilateral horizontal fracture lines of the pars interarticularis, leading to separation of the anterior-posterior spinal elements 100% 50%
 
Presentation
  • History 
    • commonest mechanisms (Allen and Ferguson classification)
      • extension-compression
      • lateral flexion
        • results in Type B Comminuted subtype
      • flexion-distraction
  • Symptoms
    • neurologic symptoms common (up to 66%)
      • radicular pain, radiculopathy or spinal cord injury/myelopathy
      • can be classified by Frankel grade or ASIA impairment scale
  • Physical exam
    • inspection
      • torticollis, paravertebral muscle spasm
    • neurovascular
      • radicular pain and numbness
      • myelopathy
Imaging
  • Radiographs 
    • recommended views
      • AP, lateral, oblique views
    • findings
      • disc space narrowing
      • often difficult to detect on plain radiographs
      • instability 
        • >3.5mm displacement
        • >10deg kyphosis
        • >10deg rotation difference compared with adjacent vertebra
    • sensitivity and specificity
      • low sensitivity 
        • 38% pickup rate on plain radiographs
  • CT 
    • indications
      • to further evaluate fracture morphology
        • fracture line extends
          • rostrally/caudally into adjacent superior/inferior facets
          • ventrally into foramen transversarium, transverse process and pedicle
          • dorsally into lamina
    • findings
      • translation of fractured/adjacent vertebrae in sagittal and coronal planes
      • uncovertebral joint subluxation
      • degree of vertebral body destruction
  • MRI 
    • findings
      • disruption of ligaments
        • 50-75% rupture of anterior longitudinal ligament (ALL
        • 30-35% disruption of posterior longitudinal ligament  (PLL)
        • 10-75% disruption interspinous and supraspinous ligaments (ISL and SSL)
      • disruption of intervertebral disc 
      • bone bruising
Treatment
  • Nonoperative
    • NSAIDS, rest, immobilization
      • indications
        • stable injuries without neurological deficit
        • hyperextension/rotation is poorly immobilized in a halo
      • techniques
        • Miami J collar
        • halo vest
      • outcomes
        • long term results of non-operative treatment are less desirable
        • may be successful in the absence of instability
        • surveillance is necessary to detect late instability and persistent pain
        • spontaneous fusion rate is only 20%
  • Operative
    • posterior decompression and two-level instrumented fusion 
      • indications
        • most cases require surgery
        • main injured structures are posterior, thus preferred approach is posterior
        • also indicated for nonoperatively managed cases with late instability and persistent pain
      • techniques
        • two-level lateral mass or pedicle screw and rod fixation  
        • lateral mass plating  
      • outcomes
        • risk of anterior disc space collapse and late kyphotic deformity
        • midline fusion does not control rotation
    • two-level ACDF
      • indications
        • if mostly reduced and dont need posterior approach to obtain direct reduction
        • controls anterior collapse and rotation
      • techniques
        • using iliac crest bone graft 
    • single posterior pedicle screw  
      • indications
        • Type A Separation fracture without instability
    • anterior and posterior decompression and fusion
      • indications
        • if additional anterior column support is needed
        • if anterior approach is attempted initially, with unsuccessful reduction because of complicated fracture morphology or late presentation
Complications
  • Vertebral artery injury
    • from pedicle screw placement
  • Late kyphotic deformity
  • Late instability (anterior translation)
  • Chronic neck pain and radiculopathy
 

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