Where should the CR enter the patient for the AP projection of the ankle joint?

Citation, DOI & article data

Citation:

Murphy A, Bickle I, Er A, et al. Foot (lateral view). Reference article, Radiopaedia.org (Accessed on 14 Dec 2022) https://doi.org/10.53347/rID-44805

The lateral foot projection is part of the three view series examining the phalanges, metatarsals and tarsal bones that make up the foot. This view additionally examines the talocrural joint.

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This view is useful in the assessment for joint abnormalities, determining the degree of dorsal or plantar displacement in fractured bones, soft tissue effusions or gas (i.e. osteomyelitis) and in locating opaque foreign bodies.

• the patient may be supine or upright depending on comfort 
• the affected leg is externally rotated until the distal limb is parallel to the table, in many cases, the patient will have to half roll onto the affected side
• the lateral aspect of the foot will be in contact with the image receptor 
• the non-affected side is kept posterior to prevent over rotation 
• the foot is in slight dorsiflexion 
• the planter surface should be perpendicular to the image receptor 

• mediolateral projection
• centering point
  • base of metatarsals or midfoot 
• collimation
  • anteriorly to skin margin of the distal phalanges
  • posteriorly to skin margin of the calcaneus
  • superior to the talocrural joint
• orientation  
  • landscape
• detector size
  • 18 cm x 24 cm
• exposure
  • 55-60 kVp
  • 4-6 mAs
• SID
  • 100 cm
• grid
  • no

• the metatarsals are almost completely superimposed with only the tuberosity of the 5th metatarsal seen in profile 
• the domes of the superior aspect of the talus are superimposed 
• tibiotalar joint is open

If the patient has a larger distal limb it may be difficult to position it parallel to the image receptor, in these cases a foam block can be used to raise the height of the foot to maintain an optimal position. 

Anterior-posterior malalignment of the talar domes is due to over or under rotation of the foot. To adjust this, check the heel is not raised too far or alternately the toes if the patient cannot correct this position it can be aided with a small wedge sponge.

Related articles: Imaging in practice

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Citation, DOI & article data

Citation:

Gorton S, Bell D, Er A, et al. Ankle (lateral view). Reference article, Radiopaedia.org (Accessed on 14 Dec 2022) https://doi.org/10.53347/rID-40861

The ankle lateral view is part of a three view ankle series; this projection is used to assess the distal tibia and fibula, talus, navicular, cuboid, the base of the 5th metatarsal and calcaneus.

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This projection aids in evaluating fractures, dislocations and joint effusions surrounding the ankle joint, and helps to assess the severity of a calcaneal fracture by measuring the Böhler angle and Gissane angle.

• patient is in a lateral recumbent position on the table
• the lateral aspect of the knee and ankle joint should be in contact with the table resulting in the tibia lying parallel to the table
• the leg can be bent or straight 
• foot in dorsiflexion 
• place the opposite leg behind the injured limb to avoid over-rotation

• mediolateral projection
• centering point
  • the bony prominence of the medial malleolus of the distal tibia
• collimation
  • anteriorly from the hindfoot to extent of the skin margins of the most posterior portion of the calcaneus
  • superior to examine the distal third of the tibia and fibula
  • inferior to the skin margins of the plantar aspect of the foot
• orientation  
  • portrait
• detector size
  • 18 cm x 24 cm
• exposure
  • 50-60 kVp
  • 3-5 mAs
• SID
  • 100 cm
• grid
  • no

The distal fibula should be superimposed by the posterior portion of the distal tibia.

The talar domes should be superimposed allowing for adequate inspection of the superior articular surface of the talus.

The joint space between the distal tibia and the talus is open and uniform.

Superior-inferior malalignment of the superior aspect of the talus is resultant of the tibia not lying parallel to the image receptor. To adjust this, either lower the knee to suit the ankle better or place the ankle on a small wedge sponge to better suit the knee. 

Anterior-posterior malalignment of the talar domes is due to over or under rotation of the foot. To adjust this, check that the heel or the toes are not raised too far up. If the patient cannot correct this position, it can be aided with a small wedge sponge.

In trauma, it may not be possible to place the patient as above, in these cases, the same principles can be applied with a modified horizontal beam view. The patient can remain supine with an image receptor placed vertically adjacent to the lateral aspect of the upright ankle, and the x-ray beam is directed horizontally, centered at the bony prominence of the medial malleolus of the distal tibia.

References

Related articles: Imaging in practice

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