ankle (mortise view)

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The ankle AP mortise (mortice is equally correct) view is part of a three view series of the distal tibia, distal fibula, talus and proximal 5 metatarsal.

Indications

This projection is the most pertinent for assessing the articulation of the tibial plafond and two malleoli with the talar dome, otherwise known as the mortise joint of the ankle .

The most common indication is a trauma to the ankle in the setting of suspected ankle fractures and/or dislocations including talar fractures.

Other indications include:

  • assessment of fragment position and implants in postoperative follow up
  • evaluation of fracture healing
  • osteochondral injuries of the talus
  • osteoarthritis of the ankle

Patient position

  • the patient may be supine or sitting upright with the leg straightened on the table
  • the leg must be rotated internally 15°to 20°, thus aligning the intermalleolar line parallel to the detector. This usually results in the 5toe being directly in line with the center of the calcaneum
  • internal rotation must be from the hip; isolated rotation of the ankle will result in a non-diagnostic image
  • foot should be in slight dorsiflexion

Technical factors

  • anteroposterior projection
  • centering point
    • the midpoint of the lateral and medial malleoli
  • collimation
    • laterally to the skin margins
    • superiorly to examine the distal third of the tibia and fibula
    • inferior to the proximal aspect of the metatarsals
  • orientation  
    • portrait
  • detector size
    • 24 cm x 30 cm
  • exposure
    • 50-60 kVp
    • 3-5 mAs
  • SID
    • 100 cm
  • grid
    • no

Image technical evaluation

The lateral and medial malleoli of the distal fibula and tibia, respectively, should be seen in profile.

Uniformity of the mortise joint should be seen without any superimposition of either malleolus.

The base of the 5metatarsal must be included in the inferior aspect of the image.

Practical points 

In Australia, the mortise view is part of a three-part ankle series, yet in other countries, including the United Kingdom, the mortise view is the primary 'AP projection' of the ankle alongside the lateral projection.

Aligning the 5 toe to the center of the calcaneus is a practical way to gauge optimal internal rotation needed to demonstrate the mortise joint. Another way to ensure correct positioning is by rotating the leg internally until the central line of the collimation field is in line with the 5 metatarsal.

Often if the foot is not in dorsiflexion, the mortise joint will not be in full profile. 

In trauma, it is important to obtain a diagnostic mortise view for the proper assessment of the mortise joint. Trauma patients may not have the ability to rotate their lower limb internally, in this case, the x-ray beam can be angled 15-20° medially to achieve the view although this will result in some artifactual elongation of structures.

Fractures of the 5 metatarsal may also be seen and the medial clear space might be assessed in this view .

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