Pelvis (outlet view)

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

Indications

The outlet view is of considerable importance in the management of severely injured patients presenting to emergency departments ^1-5.  This particular view allows for assessment of the cephalic/caudal translation and superior migration of the hemipelvis following trauma ². It can also be used to further demonstrate suspected fractures or lesions of the pubic rami.

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 imaging field

Technical factors

• anteroposterior axial projection
• centering point
  • 5 cm distal to the superior pubic symphysis border
  • the central ray is angled 20-35° cephalic for males and 30-45° for females (see figures 2 and 3)
  • ensure primary beam 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 pelvis is imaged from superior of the iliac crest to the proximal shaft of the femur
• the pubic symphysis should be central to the image with little to no patient rotation
• there is a clear demonstration of both the anterior and inferior pubic ramus with little to no foreshortening

Practical points

• internal rotation can be assisted with the use of sandbags over the lateral edges of the patient's feet, only if a femoral neck fracture is not suspected
• the patient may appear rotated due to an underlying injury rather than malpositioning
• remember to align your image receptor with the central ray, angles of up to 45° can result in significant image receptor displacement superiorly
• the use of AEC in this projection is debatable; it is commonly best to adjust your exposure based on the AEC readout from the AP pelvis