Lesson

Investigation

X-Ray

Standard X-ray images of the ankle should include an anteroposterior (AP) view, a mortise view and a lateral view. The mortise view is not a true AP that profiles the ankle joint without the fibula overlapping.

In the acute setting, ankle X-ray are indicated if there is bony tenderness according to the Ottawa Ankle Rules or if the patient is unable to bear weight both immediately following the injury and at the time of the subsequent clinical assessment. Followed correctly, the Ottawa Ankle Rules detect all clinically significant fractures (100% sensitivity).2

Ottawa Ankle Rules

An ankle X-ray is only required if there is any pain in the malleolar zone and any one of the following:

  • Bone tenderness along the distal 6 cm of the posterior edge of the tibia or tip of the medial malleolus, OR
  • Bone tenderness along the distal 6 cm of the posterior edge of the fibula or tip of the lateral malleolus, OR
  • An inability to bear weight both immediately and in the emergency department for four steps.

Other views of the ankle that can be useful include:

  • Anterior or posterior impingement views. These are lateral views in plantarflexion (for posterior) or dorsiflexion (for anterior impingement) that help determine the degree to which bony factors contribute to ankle impingement.
  • Weight-bearing views. These help in assessing articular cartilage loss, subluxation at the ankle joint, and diastasis (widening) of the distal tibiofibular syndesmosis.
  • Lazy lateral view. The lateral malleolus is projected behind the medial malleolus. The lateral tubercle of the posterior process of the talus, or os trigonum is profiled.
  • AP view of the proximal fibula. This view should be used whenever a Maisonneuve fracture is suspected.
  • Stress views with inversion, eversion and anterior drawer stress views may highlight ligamentous instability.

Click on the following images to view a normal ankle X-ray series.

  • XR RIGHT ANKLE AP + MORTISE

    Click to see the larger version

  • XR RIGHT ANKLE LATERAL

    Click to see the larger version

Other imaging

Other imaging studies are usually not indicated in the acute phase.

Ultrasound can be very useful in defining the peroneal and tibialis posterior tendons as well as the Achilles tendon. It can also show the ligamentous structures around the ankle.

As with other body parts, MRI is the best single investigation for the majority of acute and overuse ankle problems. It visualises the ankle ligaments and tendons very well and is also the modality of choice for assessing the talar dome. CT is the best option for bony details and can be very helpful in the preoperative assessment of ankle fractures.

Click on the following images to review normal USS, CT and MRI images of the ankle.

  • A normal ATFL

    Note the uniform thickness and texture on this USS image

  • A normal ATFL

    on this T1 axial sequence

  • A normal CFL

    on a coronal fat-sat image

  • A normal AITFL (large arrow) and PITFL (small arrow)

    on this axial MRI image