Cervical spine (odontoid view)

Dr Henry Knipe and Andrew Murphy et al.

The odontoid or 'peg' projection is an AP projection of C1 (atlas) and C2 (axis).

  • patient positioned erect in AP position unless trauma the patient will be supine
  • patient’s shoulders should be at equal distances from the image receptor to avoid rotation, the head facing straight forward.
  • at the last instant, the patient is instructed to open their mouth as wide as possible 
  • the head should be positioned so the lower margin of the upper incisors and the base of the skull are perpendicular to the image receptor
    • do not move the head in trauma, angle the central accordingly 
  • anterior-posterior projection
  • centring point
    • the central ray is centred at the centre of the open mouth
    • angle accordingly; see 'patient positioning'
  • collimation
    • laterally to include the mandible
    • superior-inferior to include the upper incisors and lower incisors 
  • orientation
    • landscape
  • detector size
    • 18 cm x 24 cm
  • exposure
    • 75 kVp
    • 8-10 mAs
  • SID
    • 100 cm 
  • grid
    • yes
  • the dens is free from superimposition
  • the zygapophyseal joint space between C1 and C2 is symmetrical
  • make sure that any removable artefacts such as earrings, glasses or metal dentures are removed to avoid obscuring the anatomy of interest

If teeth are superimposed over the upper aspect of the dens, the head needs to be hyperextended or in the case of trauma, the central ray should be angled cephalic.

If the base of skull is superimposed over the upper aspect of the dens, the head needs to be hyperflexed or in the case of trauma, the central ray should be angled caudal

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Article information

rID: 58730
Section: Radiography
Synonyms or Alternate Spellings:

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Cases and figures

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    Figure 1: supine peg view
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