Scaphoid (PA view)

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The posteroanterior scaphoid view is part of a four view series of the scaphoid, wrist and surrounding carpal bones. Although performed PA, the view can often be referred to as an AP view.

Indications

This view aims to show the scaphoid in its anatomical position, hence allowing the visualization of any subtle distal, middle or proximal fractures  of the scaphoid.

Patient position

  • patient is seated alongside the table
  • the affected arm if possible is flexed at 90° so the arm and wrist can rest on the table
  • the affected hand is placed, palm down on the image receptor with hand in ulnar deviation (see practical points)
  • shoulder, elbow, and wrist should all be in the transverse plane, perpendicular to the central beam
  • the wrist and elbow should be at shoulder height which makes radius and ulna parallel (lowering the arm makes radius cross the ulna and thus relative shortening of radius)

Technical factors

  • posteroanterior projection
  • centering point
    • anatomical snuffbox 
  • collimation
    • laterally to the skin margins
    • distal to the midway up the metacarpals
    • proximal to the include one-quarter of the distal radius and ulna
  • orientation  
    • portrait
  • detector size
    • 18 cm x 24 cm
  • exposure
    • 50-60 kVp
    • 3-5 mAs
  • SID
    • 100 cm
  • grid
    • no

Image technical evaluation

  • hand is in ulnar deviation with little superimposition over the scaphoid bone
  • minor superimposition of the metacarpal bases
  • articulation between the distal radius and the ulna is open or has little superimposition
  • concavity of the metacarpal shafts is equal

Practical points

As scaphoid fractures are associated with FOOSH injuries, it is desirable in the acute setting to collimate to include the wrist in the PA view, covering all areas around the scaphoid that could be the source of pain. In a follow-up radiograph, coning down to the scaphoid is favored.

Ulnar deviation is necessary as it moves the scaphoid away from the radius and rotates it in the palmer aspect, minimizing superimposition and achieving a pure PA projection . Patients with a fractured scaphoid will be in a lot of pain so deviating their hand to the ulna can be quite a task; only deviate the hand as much as the patient can bear it.

More often than not, the pain has not been addressed yet. Offer to move things around to assist in positioning - simple things like lowering/raising the table can go a long way and result in a better experience for the patient. It is important to remember this when examining your patient, as it is easy to forget that simply lifting your hand up and placing it on an image receptor could result in substantial pain.