Weightbearing DP foot radiograph

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The weightbearing dorsoplantar foot radiograph is a specialized projection of the foot. Nonweightbearing views (e.g. DP foot) are inadequate for the assessment of alignment because the bones of the feet are not in a functional position.

Indications

This view is key to the assessment of foot alignment and the diagnosis of abnormalities causing malalignment and foot pain, i.e. Lisfranc injury. Bilateral projections may be requested for comparison purposes.

Patient position

  • foot is planted on the detector with the lower leg perpendicular to the floor (weightbearing surface)
  • patient distributes weight evenly across both feet

Technical factors

  • dorsoplantar projection
  • centering point
    • ​base of the third metatarsal
    • central beam is angled approximately 15-20 degrees towards the heel to minimize projecting the tibia and fibula over the hindfoot
  • collimation
    • anterior to the skin margins of the distal phalanges 
    • medial/lateral to the skin margins
    • posterior to the calcaneum 
  • orientation  
    • ​portrait
  •  detector size
    • 18 cm x 24 cm
  • exposure​
    • 50-60 kVp
    • 3-6 mAs
  • SID
    • 100 cm
  • grid
    • no

Image technical evaluation

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

Practical points

As these views are often requested to rule out Lisfranc injuries, remember to encourage your patient to place normal, even weight distribution on their feet, instead of forcing their weight on them.

Ensure ample warning is provided to the patient of the x-ray tube's close proximity to their torso. To prevent patients from burning themselves, remind them not to use the often overheated tube as weight support.

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

  • if the foot is too externally rotated, the metatarsal bases will be heavily superimposed whilst the tuberosity of the navicular bone can be seen in profile
  • too much internal rotation will open up the metatarsal bases, with the resultant image bearing close resemblance to the medial oblique projection

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