Revision 4 for 'Sacroiliac joint (PA oblique view)'

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Sacroiliac joint: PA oblique view

 The PA oblique view of the sacroiliac joints can be performed in patients who cannot assume the supine position. Both sides of the sacroiliac joints are examined for comparison. Oblique views can be taken either AP or PA.

Patient position

  • patient positioned semi-prone with a flexed knee can usually support for this position
  • the side being examined is closer to the image receptor, therefore use the RAO position to demonstrate the right joint space and the LAO position to demonstrate the left joint space
  • the degree of obliquity is approximately 25-30°

Technical factors

  • posteroanterior oblique projection
  • centring point
    • perpendicular to the image receptor, centring 1 cm medial to the posterior inferior iliac spine closest to the image receptor.
  • collimation
    • laterally to include the entire sacroiliac joint of interest
    • superiorly and inferiorly to include the entire joint
  • orientation
    • portrait
  • detector size
    • 18 cm x 24 cm
  • exposure
    • 75 kVp
    • 25-30 mAs
  • SID
    • 100 cm
  • grid
    • yes                                                                  

Image technical evaluation

  • the sacroiliac joint closest to the image receptor should be shown open or with minimal superimposition of the ilium and the sacrum
  • joint is centered on the radiograph

Practical points

  • the degree of obliquity required to show the sacroilliac joint in an PA oblique position is usually shallow (25-30°)
  • a radiolucent support such as a sponge can be used to help elevate the hip and thorax to maintain position

  • a 20-25° caudal angle, centered to posterior inferior iliac spine will project the central ray perpendicular to the long axis of the sacro-iliac joint.

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