What is the central-ray angulation for the axial (plantodorsal) projection of the calcaneus?

Citation, DOI & article data

Citation:

Murphy, A. Calcaneus (axial view). Reference article, Radiopaedia.org. (accessed on 13 Sep 2022) https://doi.org/10.53347/rID-44851

The calcaneus axial view is part of the two view calcaneus series assessing the talocalcaneal joint and plantar aspects of the calcaneus.

As technology advances, computed tomography (CT) has widely been used 1 to better visualize and characterize calcaneum fragment displacements and fracture lines. Yet, there remain many institutions (especially in rural areas) where CT is not readily available.

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This projection is best used to visualize pathologies or fractures resulting in medial or lateral displacement 2. Its diagnostic sensitivity for calcaneus fractures is 87% 3. 

• patient is supine or seated with the affected limb extended 
• the posterior aspect of the ankle is resting on the image receptor 
• foot is dorsiflexed until the plantar surface is running perpendicular to the image receptor 
• dorsiflexion can be aided with tape or fabric wrapped around the distal phalanges to be pulled backwards by the patient, this should only be performed if the patient can tolerate it 

• plantodorsal projection
• centering point
  • the central ray is angled 40° cephalad from the long axis of the foot centered at the base of the 3rd metatarsal (midfoot)
• collimation
  • lateral to the skin margins
  • anterior to distal third of the foot
  • posterior to the skin margins of the calcaneus 
• orientation  
  • portrait
• detector size
  • 18 cm x 24 cm
• exposure
  • 60-70 kVp
  • 8-15 mAs
• SID
  • 100 cm
• grid
  • no

• entire calcaneus is visible from the posterior tuberosity to the talocalcaneal joint
• sustentaculum tali is evident on the medial aspect of the image
• subtalar joint should be visible on the superior portion of the image

Although it is preferred to have the patient's foot in full dorsiflexion, many times this will not be possible due to pain. In these scenarios, it is just as effective to:

• increase the angle to compensate for lack of dorsiflexion
• raise the distal part of the leg (placing an immobilization sponge posteriorly), ensuring the knee joint is kept extended

References

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