Updated: 6/23/2021

Occipitocervical Instability

0%
Topic
Review Topic
0
0
N/A
N/A
Questions
4
0
0
0%
0%
Evidence
12
0
0
0%
0%
Videos / Pods
1
0%
0%
Cases
1
Topic
Images
https://upload.orthobullets.com/topic/2014/images/powers_ratio_ct_scan.jpg
https://upload.orthobullets.com/topic/2014/images/ocjd.jpg
https://upload.orthobullets.com/topic/2014/images/49_moved.jpg
  • Summary
    • Occipitocervical instability can be traumatic or aquired through a degenerative process such as rheumatoid arthritis or Down's Syndrome.
    • Diagnosis is usually confirmed with a combination of CT scan, MRI, and lateral flexion-extension radiographs.
    • Traumatic instability is treated with occipitocervical fusion. Aquired instability is treated with observation or occipitocervical fusion depending on the presence of neurologic deficits.
  • Epidemiology
    • traumatic occipitocervical instability
      • incidence
        • ~15-30% of cervical spine injuries occur at the occipitocervical junction
      • prevalence
        • identified in 19% fatal cervical injuries
    • acquired occipitocervical instability
      • most frequently seen in Down syndrome population
      • usually asymptomatic and identified in screen for surgery or special olympic participation
  • Etiology 
    • Terminology
      • also called
        • atlanto-occipital dissociation (AOD)
        • occipitocervical dislocation
    • Pathophysiology
      • traumatic
        • mechanism of injury
          • high-energy trauma
          • translation or distraction injuries that destabilize the occipitocervical junction
        • pathoanatomy
          • head most often displaces anteriorly
      • acquired
        • pathoanatomy
          • due to bony dysplasia or ligament and soft-tissue laxity
    • Associated conditions
      • atlantoaxial instability
        • also seen in Down syndrome patients
      • neurologic deficits
      • vertebral or carotid artery injuries
      • Down Syndrome
  • Anatomy
    • Osteology
      • morphology
        • occipital condyles are paired prominences of the occipital bone
        • oval or bean shaped structures forming lateral aspects of the foramen magnum
      • joint articulations
        • intrinsic relationship between occiput, atlas and axis to form the occipitoatlantoaxial complex or CCJ
        • 6 main synovial articulations
          • anterior and posterior median atlanto-odontoid joints
          • paired occipitoatloid joints
          • paired atlantoaxial joints
    • Ligaments
      • intrinsic ligaments are located within the spinal canal, provide most of the ligamentous stability. They include
        • transverse ligament
          • primary stabilizer of atlantoaxial junction
          • connects the posterior odontoid to the anterior atlas arch, inserting laterally on bony tubercles.
        • paired alar ligaments
          • connect the odontoid to the occipital condyles
          • relatively strong and contributes to occipitalcervical stability
        • apical ligament
          • relatively weak midline structure
          • runs vertically between the odontoid and foramen magnum.
        • tectorial membrane
          • connects the posterior body of the axis to the anterior foramen magnum and is the cephalad continuation of the PLL
    • Vascular system
      • occipital condyles in proximity to vertebral arteries
    • Nervous system
      • proximity of the occipital condyles to:
        • medulla oblongata
        • spinal cord
        • lower cranial nerves (CN IX - CN XII)
  • Classification
    • Traynelis Classification (direction of displacement)
      Type 
      Anterior occiput dislocation
      Type II
      Longitudinal dislocation
      Type III
      Posterior occiput dislocation
    • Harbourview Classification System (degree of instability)
      Stage I
      Minimal or non-displaced, unilateral injury to craniocervical ligaments
      Stable
      Stage II
      Minimally displaced, but MRI demonstrates significant soft-tissue injuries. Stability may be based on traction test
      Stable or Unstable
      Stage III
      Gross craniocervical misaligment (BAI or BDI > 2mm beyond normal limits)
      Unstable
  • Imaging
    • Radiographs
      • recommended views
        • AP, lateral and odontoid views
      • findings
        • low sensitivity in detecting injury (57%)
      • measurements
        • used to diagnosis occipitocervical dislocation
          • Powers ratio = C-D/A-B
            • C-D: distance from basion to posterior arch
            • A-B: distance from anterior arch to opisthion
              • significance
                • ratio ~ 1 is normal
                  • if > 1.0 concern for
                    • anterior dislocation
                  • ratio < 1.0 raises concern for
                    • posterior atlanto-occipital dislocation
                    • odontoid fractures
                    • ring of atlas fractures
          • Harris rule of 12
            • basion-dens interval or basion-posterior axial interval
              • >12mm suggest occipitocervical dissociation
    • CT
      • indications
        • considered gold standard for osseous injuries of the spine
      • views
        • midsaggital CT reconstruction
    • CT angio
      • indications
        • evaluate for injury to vertebral artery
        • identify anatomy of vertebral artery prior to occipitocervical fusion
    • MRI
      • indications
        • suspected ligamentous injury with preserved alignment or occult injury
        • neurological deficits
  • Treatment
    • Nonoperative
      • provisional stabilization while avoiding traction
        • indications
          • traumatic instability with distraction of the occipitoatlantal joint
        • techniques
          • halo vest
          • tongs
          • prolonged cervical orthosis is not recommended due to poor stabilization of the AOJ
        • outcomes
          • use of traction should be avoided in most cases
          • traction may be considered in stage 2 injuries when MRI demonstates soft-tissue injury with perserved aligment
    • Operative
      • occipitocervical fusion
        • indications
          • most traumatic cases require stabilization
          • acquired cases when evidence of myelpathy or significant symptomatic neck pain
          • invagination and atlanto-axial impaction secondary to inflammatory arthropathy (e.g., rheumatoid arthritis)
          • tumor
  • Technique
    • Occipitocervical fusion
      • approach
        • posterior midline incision with patient in prone position
        • Mayfield retractor used to obtain proper craniocervical alignment
          • establish preoprative 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 disect above the posterior arch of C1 more than 1 cm lateral to midline to avoid injury to vertebral artery
      • instrumentation
        • length
          • posterior segental 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
        • may require bone grafting or removal of boney fragments compressing neurovascular structures.
  • Complications
    • Nonunion
      • Internal Carotid Artery
      • Vertebral Artery
Flashcards (0)
Cards
1 of 0
Questions (4)
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK

(OBQ10.200) A 27-year-old female with Down's presents with neck pain, progressive gait instability, and loss of fine motor dexterity in her hands. Flexion and extension radiographs are shown in Figure A and B and demonstrate occipitocervical instability. When performing an occipitocervical fusion, what location in Figure C is most appropriate for placement of an 8mm unicortical screw?

QID: 3293
FIGURES:
1

A

5%

(201/4115)

2

B

52%

(2151/4115)

3

C

9%

(388/4115)

4

D

18%

(746/4115)

5

E

15%

(598/4115)

L 4 D

Select Answer to see Preferred Response

Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Evidence (12)
VIDEOS & PODCASTS (1)
CASES (1)
EXPERT COMMENTS (11)
Private Note