The ankle joint consists of three bones – the tibia, the fibula, and the talus.
The ankle also consists 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 held together by ligaments).
There are three main sets of ligaments:
- Medial: deltoid ligament
- Lateral: posterior talofibular, anterior talofibular and calcaneofibular ligaments
- Syndesmotic ligament
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, so it’s important not to miss them.
2. Pay particular attention to the fibula on the lateral view for an oblique fracture.
3. Look at the mortise and the talar dome.
Ensure the space is uniform and that the talar dome surface is smooth.
4. Look at the interosseous 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.
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 20-40°
- If it’s less than 20°, then consider a calcaneus fracture
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 ankle fractures
The level of the fracture directs the treatment – fractures can be classified according to the Salter-Harris classification.
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). Many recommend treating it 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 one month, 72.1% had full weight-bearing activity, and by three 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 Salter-Harris I if your department stocks them. (See a full summary of this article on ALiEM).
Medial malleolus fracture
An undisplaced distal tibia (Salter-Harris I or II) can be managed with a long leg cast and non-weight bearing. SH3 or 4 needs discussion with ortho. All will have a 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). Many recommend treating it as a fracture even if no radiographic fracture is noted.
The most common distal tibial epiphysis injury is a Salter-Harris II
The high occurrence of Salter-Harris III and IV 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, the patient can have a long leg cast and be non-weight bearing, with ortho discussion and follow-up. If there is >2mm displacement, an ortho review will be required as this often needs operative management.
A pilon fracture is an axial load on the tibia, and the talus is pushed into the tibia plafond.
If the fracture is non-displaced or 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, surgery may be required to avoid non-union, so speak to the ortho team.
Posterior malleolus fracture
Usually, when this happens, there is also a lateral malleolus fracture (because they share ligament attachments). The ankle can be unstable if a large piece is broken, and 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 is usually treated with a short leg cast, and weight-bearing is avoided for six weeks.
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.
If two parts of the malleoli are broken, then the ankle is not stable and surgery is usually needed.
If all three malleoli are broken, then there can be associated dislocation. The ankle will be unstable and will require ortho input.
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.
In adults, this can be managed with a long leg cast, but in children, it will require operative fixation.
Ligaments hold together the joints between the tibia and fibula. If this ligament is sprained, then this is a syndesmotic injury.
As mentioned above, there can be a 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 an overlap of the fibula and the anterior tibial tubercle (>6mm on the AP views, >1mm on the mortise.
When do I need an immediate orthopaedic review?
- Open fracture
- Salter-Harris III or IV
- Neurovascular injury
- Compartment syndrome
- Unable to reduce the fracture
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, so it is important to follow up ankle fractures post-injury.
(Ed: Thanks to Eyston Vaughan-Huxley for his input too).