Foot (dorsoplantar view)

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The dorsoplantar view is part of a three view series examining the phalanges, metatarsals and tarsal bones that make up the foot.

Indications

This view demonstrates the location and extent of fractures in the foot, joint space abnormalities, soft tissue effusions and is the frontal view for the examination of foreign bodies.

Patient position

  • the patient may be supine or upright depending on comfort
  • the affected leg must be flexed enough that the plantar aspect of the foot is resting on the image receptor

Technical factors 

  • AP projection
  • centering point
    • x-ray beam centered to the base of the 3 metatarsal
    • the beam must be angled approximately 10° posteriorly towards the calcaneum to mimic the arch of the foot, this may change if the arch is high or flat
  • collimation
    • lateral to the skin margins
    • anterior to the skin margins of the distal phalanges
    • posterior to the skin margins of the calcaneum
  • orientation  
    • portrait
  • detector size
    • 18 cm x 24 cm
  • exposure
    • 50-55 kVp
    • 3-4 mAs
  • SID
    • 100 cm
  • grid
    • no

Image technical evaluation

  • 1metatarsal has even concavity
  • the spaces between the 2 to 5 metatarsal are equal, yet the bases are overlapping
  • intertarsal space between the medial and intermediate cuneiform should be open

Practical points

The bases of the metatarsals and the tarsal bones are the most reliable rotation indicator on the DP view.

If the foot is over rotated externally, the metatarsal bases will be heavily superimposed whilst the tuberosity of the navicular bone can be seen in profile.

Over rotation internally will open up the metatarsal bases and the resultant image will bear close resemblance to the medial oblique projection.

In the scenario where the DP is ordered to query a foreign body, do not angle the x-ray beam to mimic the arch as this will result in elongation of the foreign body in question.

In trauma, the patient may not be able to flex the affected knee to the desired angle. In this case, a triangular wedge can be placed under the foot. The same principle of angling posteriorly to mimic arch applies. With the foot resting at 10-15° less of an angle is required.