How many degrees and in which direction should the C arm be tilted for the PA projection of the C spine during an Acdf procedure?

Citation, DOI & article data

Citation:

Nguyen, M., Murphy, A. Cervical spine (PA oblique view). Reference article, Radiopaedia.org. (accessed on 08 Sep 2022) https://doi.org/10.53347/rID-51499

The PA oblique cervical spine projections are supplementary views to the standard AP, odontoid and lateral images in the cervical spine series and are always done bilaterally for comparison purposes. The PA oblique projection is preferred as it reduces radiation dose to the thyroid 1, compared to the AP oblique projection.

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This projection can be used to visualize pathology involving the adjacent soft tissue structures or cervical spine, especially stenosis of the intervertebral foramina.

Note: Such views should not be performed on trauma patients without the strict instructions of a qualified clinician who has reviewed the lateral cervical spine image or CT of the cervical spine. Moving the patient's head or neck, or removing a cervical collar could be detrimental.

• patient is standing erect with either their right or left anterior side closer to the image receptor
• the thorax and cervical vertebral column at 45° to the image receptor
• head in a lateral position

• posteroanterior oblique projection  
• centering point
  • C4
  • central ray has a 15° caudal tilt
• collimation
  • laterally to include the entire cervical spine and its spinous processes
  • anteriorly to include the soft tissue of the neck
  • superiorly to include all of C1
  • inferiorly include to at least T1 (EAM to vertebral prominence of C7 and/or T1)
• orientation
  • portrait
• detector size
  • 18 cm x 24 cm
• exposure
  • 75 kVp
  • 12.5-16 mAs
• SID
  • 150-180 cm
• grid
  • yes

• all of the cervical spine should be included from C1-T1
• patient’s head should be in a lateral position to prevent mandibular superimposition over the vertebral bodies of the cervical spine. To ensure this ensure that the interpupillary line is perpendicular to the image receptor but also parallel to the floor
• intervertebral foramina of the side positioned closer to the image receptor should be demonstrated open 4 

• make sure that any removable artefacts such as earrings, glasses, tongue piercings or metal dentures are removed to avoid obscuring the anatomy of interest
• using a larger source-to-image-distance will decrease the magnification of the image and improves acuity 2

Correcting rotational errors

To demonstrate the intervertebral foramen of the c-spine open, it is necessary to achieve adequate rotation of the vertebral column, usually at 45°.

If underrotated, the foramina will be narrowed and a sternoclavicular joint would be superimposed over the vertebral column 3.

Over rotation of more than 45° would cause one pedicle to be foreshortened while the other pedicle aligns to the midline of the vertebral bodies 2.

References

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