Sacrum (AP view)

The sacrum AP view is used to demonstrate the sacrum and its articulations. It can be utilised in the event of trauma, or for evaluating degenerative change 1. The efficacy of this radiographical projection is debatable, with radiographers encouraged to follow department protocol when imaging this region 2

  • the radiograph is performed with the patient in a supine position, hands placed comfortably by the patient's side, with the legs extended 
  • ensure the patient is not rotated- ASIS must be equidistant from the IR/table.
  • AP view
  • centring point
    • at the MSP, midway between the ASIS and the symphysis pubis 3
  • central ray
    • angled 15 degrees cephalic 3
    • this angle allows the CR to be perpendicular to the sacrum as it is curved with an anterior concavity and convex posteriorly 
  • collimation
    • must adhere to the ALARA principle given the region exposed via the primary beam 
    • superior to include the L5/S1 articulation
    • inferior to include the S5 ( the articulation of the sacrum and coccyx will not be demonstrated clearly given the orientation of the coccyx in this projection) 
    • lateral to include the SI joints
  • orientation  
    • portrait 
  • detector size
    • 24x30 cm 
  • exposure
    • 70 kVp
    • 20-30 mAs 
  • SID
    • 110 cm
  • grid
    • yes (ensure the correct grid is selected if using focused grids)
    • when using table bucky, ensure the CR and the IR are correctly aligned, given the use of an angled tube 
  • the entire sacrum should be visible from S1-S5 
  • not patient rotation as demonstrated by the symmetrical appearance of the SI joints and the iliac crests 
  • adequate penetration as evident by the clear visualisation of the sacral foramen 
  • the sacral foramen should appear open, which is achieved using the correct tube angle
  • always consider department protocol before undertaking in imaging of the sacrum 
  • often overlying bowel gas can obscure the bony anatomy of the sacrum, making interpretation difficult
  • the sacrum is an area which should be reviewed on trauma pelvis radiographs, paying particular awareness to the arcuate lines
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Article information

rID: 49742
Section: Radiography
Tag: snippet
Synonyms or Alternate Spellings:

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Cases and figures

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    Sacrum anterior v...
    Figue 1: bony pelvis
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    Sacrum posterior ...
    Figure 2: bony pelvis
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    Case 1: bone island (small - sacral ala - xray)
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    Case 2: normal sacrum X-rays
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    Case 3: pelvis annotated x-ray
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