Pelvis (inlet view)

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The AP inlet view is part of a pelvic series examining the iliac crest, sacrum, proximal femur, pubis, ischium and the great pelvic ring.

Indications

It is of considerable importance in the management of severely injured patients presenting to emergency departments . This particular view is perpendicular to the pelvic rim, allowing for assessment of any suspected narrowing or widening of that rim. Additionally, it is used to assess the anterior-posterior displacement of pubic rami fractures.

Patient position

  • patient is supine
  • lower limbs are internally rotated 15-25° from the hip (do not attempt this if a fracture is suspected)
  • patient's hands are out of the way of the imaging field

Technical factors

  • AP superoinferior projection
  • centering point
    • midline at the level of the anterior superior iliac spine
    • the central ray is angled 25-40° caudal to be perpendicular to the plane of the pelvic inlet
    • ensure central ray is aligned with the image receptor
  • collimation
    • laterally to the skin margins
    • superior to above the iliac crests
    • inferior to the proximal femur
  • orientation  
    • landscape
  • detector size
    • 35 cm x 43 cm
  • exposure
    • 70-80 kVp
    • 20-30 mAs
  • SID
    • 100 cm
  • grid
    • yes

Image technical evaluation

The entirety of the bony pelvic rim is central to the image without superimposition

The iliac wings are evident on the superior portion of the image, the inferior and superior pubic rami are superimposed on the inferior portion.

Practical points

The patient may appear rotated due to an underlying injury rather than position

Remember to align your image receptor with the central ray, angles of up to 45° caudal can result in significant image receptor displacement inferiorly. The use of AEC in this projection is debatable; it is best to adjust your exposure based on the AEC read out of the AP pelvis.