Ankle protocol (CT)

Last revised by Dr Joachim Feger on 09 Sep 2021

The CT ankle protocol serves as an examination for the bony assessment of the ankle and rearfoot and is almost always performed as a non-contrast study. It can be also combined with a CT arthrogram for the evaluation of chondral and osteochondral injuries or can encompass the whole foot in certain indications.

Note: This article aims to frame a general concept of a CT protocol for the assessment of the ankle and rearfoot. Protocol specifics will vary depending on CT  scanner type, specific hardware and software, radiologist and perhaps referrer preference, patient factors e.g. implants, specific indications.

A typical CT of the ankle might look like as follows:

Typical indications include foot and ankle trauma and or the depiction of bony lesions 1-7:

The most common purpose of an ankle CT is the depiction of the bony structures and precise classification of ankle fractures, talar and calcaneal fractures including avulsion injuries 1-3.

The purpose in the setting of inflammatory and neoplastic processes is to depict bony erosions and osteolysis 4,5.

In the setting of distal tibiofibular syndesmosis injury, CT can demonstrate the position of the lateral malleolus in relation to the tibial incisure and assess tibiofibular groove morphology 7,8.

The main purpose of a CT arthrogram of the ankle is the detection and assessment of cartilage or osteochondral injury 9.

  • patient position
    • supine position
  • scout
    • mid/distal third of lower leg to the skin of the heel
  • tube voltage and tube current
    • ≤120 kV and ≤100 mAs
  • scan extent
    • variable depends on the proximal extent of the pathology
    • minimum: ~2 cm above the tibiotalar joint to the bottom of the calcaneus
  • scan direction
    • caudocranial
  • scan geometry
    • field of view (FOV): 100-160 mm (should be adjusted to increase in-plane resolution)
    • slice thickness: ≤1.5 mm, overlap ~50%
  • reconstruction kernel
    • bone kernel (e.g. B60-U70), soft tissue kernel (e.g. B40-50)
  • multiplanar reconstructions
    • axial images: perpendicular to the distal tibia and parallel to the tibiotalar joint
    • coronal images: parallel to the malleolar axis 
    • sagittal images: perpendicular to the malleolar axis 
    • axial oblique images*: posteroinferior tilt of about 45° perpendicular to the posterior facet of the calcaneus
  • footrests are advisable if tolerated by the patient especially in a setting where both ankles and/or the distal tibiofibular syndesmosis is evaluated
  • the extent of the examination can and should be tailored to the specific indication or clinical question

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