Ankle x-ray interpretation

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The ankle consists of three bones – the tibia, the fibula, and the talus.

The ankle also consist of two joints – the ankle joint (where the tibia, fibula and talus meet) and the syndesmosis joint (the joint between the tibia and fibula which is help together by ligaments).

There are three main sets of ligaments:

  • Medial: deltoid ligament
  • Lateral: posterior talofibular, anterior talofibular and calcaneofibular ligaments
  • Syndesmotic ligament

Ankle views

An x-ray of the ankle will have three views – AP, mortise, and lateral. It should be noted though, that in some countries, including the UK, only the mortise and lateral are used. See the annotated images below from WikiFoundry, and thanks also to Radiopaedia:

 

In the AP view:

  • The distal fibula should be slightly superimposed on the tibia
  • The lateral and medial malleoli should be in profile
  • The tibiotalar space should be open (although the full mortise isn’t visible)

In the mortise view:

  • This aims to assess the articulation of the ankle joint
  • The lateral and medial malleoli should be in profile
  • The mortise should be uniformly visible
  • The base of the fifth metatarsal should be included in the view

In the lateral view

  • The following bones can be assessed: tibia, fibula, talus, cuboid, navicular, calcaneus, and fifth metatarsal
  • The distal fibula should be superimposed by the posterior part of the distal tibia
  • The talar domes should be superimposed
  • The joint space between the tibia and the talus should be uniform

N.B. Assess each bone individually, and if you see a break in one, then look for a second break.

  1. Trace around the tibia and fibula in both views.

Be mindful that an ankle fracture can be unstable and therefore it’s important not to miss them.

 

2. Pay particular attention to the fibula on the lateral view for an oblique fracture.

Oblique fracture (from Radiology Key)

3. Look at the mortise and the talar dome.

Make sure the space is uniform, and that the talar dome surface is smooth.

Osteochondral fracture (from Radiopaedia)

4. Look at the interosseus ligament.

Measure the gap between the tibia and the fibula 1cm proximal to the tibial plafond. It should be less than 6mm, otherwise consider a ligament rupture which could be associated with a fracture.

Image result for interosseous ligament rupture xray

Widened gap between tibia and fibula

5. On the lateral view trace the lateral and medial malleolus, the posterior tibia, the calcaneus, and the base of the 5th metatarsal.

6. Assess the Bohler’s angle

  • Draw two lines at tangents to the anterior and posterior aspects of the calcaneus
  • The angle should be 20-400C
  • If it’s less than 200C then consider a calcaneus fracture

Calcaneus fracture (from Radiopaedia)

7. Do a final check around the bones to make sure you haven’t missed anything the first time around.

8. Remember about accessory ossicles – they aren’t fractures!

  • There are three common accessory ossicles in the ankle: os trigunum (usually forms at 7-13 years old); os subtibiale (when the medial malleolus epiphysis fails to fuse with the tibia in the later teenage years); os subfibulare (can also be an unfused ossification centre or an avulsion fracture).

Common fractures and their management

The level of the fracture directs the treatment – fractures can be classified according to the Salter-Harris classification.

Salter-Harris classification (from Radiology Assistant)

Lateral malleolus fracture

In children, a fibula fracture usually requires a short leg cast and six weeks of non-weight bearing. Salter-Harris I distal fibula fractures can be diagnosed if there is tenderness directly on the lateral malleolus (rather than the ligaments) and many recommend treating as a fracture even if no radiographic fracture is noted.

However, a study in JAMA carried out MRI scans on 135 children with presumed SH1 distal fibula fractures. All children were treated with a removable leg brace and advised to continue regular activities as tolerated. 4 of the children had an SH1 on MRI, 38 had an avulsion fracture, and the rest showed ligamentous injury or bony contusion. By 1 month, 72.1% had full weight-bearing activity and by 3 months 96.9% had returned to normal activities (it didn’t matter which type of injury they had on MRI). Therefore, a removable brace may be appropriate for a SH1, if your department stocks them. (See a full summary of this article on ALiEM).

Medial malleolus fracture

An undisplaced distal tibia (SH1 or 2) can be managed with a long leg cast and non-weight bearing. SH3 or 4 needs discussion with ortho. All will have fracture clinic follow up in a week or so.

Salter-Harris I distal tibia fractures can be diagnosed if there is tenderness directly on the medial malleolus (rather than the ligaments) and many recommend treating as a fracture even if no radiographic fracture is noted.

The most common distal tibial epiphysis injury is an SH2

The high occurrence of SH3 and SH4 fractures is because the lateral and deltoid ligaments insert here and they are stronger than the physis itself.

A Tillaux fracture is a Salter-Harris III but with avulsion of the anterolateral corner of the distal tibial epiphysis. If there is <2mm displacement then the patient can have a long leg cast, and be non-weight bearing, with ortho discussion and follow-up. If there is >2mm displacement then an ortho review will be required as typically this need operative management.

Pilon fracture

A pilon fracture is where there is an axial load on the tibia and the talus is pushed into the tibia plafond.

If the fracture is non-displaced or very distal, it is unlikely to require surgery. It would usually be treated with a short leg cast, and weight bearing would be avoided for six weeks.

If it is displaced or the ankle is unstable, then surgery may be required to avoid non-union, so speak to the ortho team.

Posterior malleolus fracture

Posterior malleolus fracture (from Wikiradiography)

Usually when this has happened, there is also a lateral malleolus fracture (because they share ligament attachments). The ankle can be unstable if a large piece is broken and therefore surgery may be indicated – so speak to the ortho team.

An untreated posterior malleolus fracture can lead to arthritis because of the disruption to the cartilage surface.

If the fracture is not displaced then it would usually be treated with a short leg cast, and weight bearing would be avoided for six weeks.

Talar neck fracture

Talar neck fracture

 

This fracture carries a high risk of avascular necrosis.

If the fracture is non-displaced then it can be managed with a short leg cast or a boot. If it is displaced then surgery will be required.

Bimalleolar fracture

Bimalleolar fracture (from Radiopaedia)

If two parts of the malleoli are broken then the ankle is not stable and surgery is usually needed.

Trimalleolar fracture

Trimalleolar fracture (from Radiopaedia)

If all three malleoli are broken then there can be associated dislocation. The ankle will be unstable and will require ortho input.

Maisonneuve fracture

This fracture is uncommon in children but can occur. It is where there is a spiral fracture of the proximal fibula along with ankle instability. On x-ray there can be syndesmotic widening.

mason1

From Wheeles Online

In adults this can be managed with a long leg cast, but in children it will require operative fixation.

Syndesmotic injury

Overlap between the tibia and fibula in a syndestomic injury (thanks to Bone School)

The joint between the tibia and fibula are held together by ligaments. If this ligament is sprained then this is a syndesmotic injury.

As mentioned above, there can be widening of the clear space between the medial border of the fibula and the lateral border of the posterior tibia (>5mm). You can also get overlap of the fibula and the anterior tibial tubercle (>6mm on the AP views, >1mm on the mortise view).

When do I need an orthopaedic review immediately?

  • Open fracture
  • Salter-Harris III or IV
  • Neurovascular injury
  • Compartment syndrome
  • Unable to reduce the fracture

Ref: RCH

Should we be worried about growth plates?

Growth arrest doesn’t occur immediately after the injury, and can even occur in seemingly benign fractures. It can be delayed for up to 6 months and so it is important to follow up ankle fractures post-injury.

References:

Wheeles Online

Radiopaedia

Royal Children’s Hospital, Melbourne

Radiology Masterclass

(Ed: Thanks to Eyston Vaughan-Huxley for his input too).

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Tessa Davis is a paediatric emergency registrar from Glasgow and Sydney, but currently living in London. Tessa tries to spend time with her 3 kids in between shifts. @tessardavis | + Tessa Davis | Tessa's DFTB posts