Algoritm for ankle fractures
The first question you should ask yourself is:
Is it a Weber type A fracture?
Is there an avulsion of the lateral malleolus. That’s easy.
If it is not a type A. Then the next question is:
Is it a Weber type B fracture?
This oblique fracture at the level of the syndesmosis is always easy to find on the x-rays.
If it is not type A or type B, then the last question is:
Can this be a Weber type C fracture?
These fractures are usually not visible on x-rays of the ankle, because the fibula fracture is too high, but the algoritm provides clues for the detection of these fractures.
When we've answered the above questions, then we end up in one of these three categories.
In each of these categories we need to determine the stage of the fracture, which tells us if the ankle is stable or unstable.
In Weber A when there is only an avulsion - or pull off fracture of the lateral malleolus (stage 1), the ankle is stable.
However when there is also a vertical - push off fracture of the medial malleolus (stage 2), then the ankle is unstable, as the ring of stability is broken in two places.
In Weber B stage 2 is stable, but stage 3 and 4 are unstable.
In Weber C finding a high fibula fracture means unstable stage 3. Since this fracture is usually not visible on x-rays of the ankle, you wanna look for stage 1 and 4, which can be a clue to image the whole lower leg to look for a high fibula fracture.
These stages in Weber B and C always follow a strict order.
This means that when you find a stage 3 fracture, there already must be a stage 1 and 2 even if you can't see them.
We will discuss these stages in the next chapter.
When you look at the image on the far left, it is easy to see that this is an unstable fracture.
There must be a rupture of the medial collateral band as the medial clear space it too wide (yellow arrow) and the anterior and posterior syndesmosis must be ruptured, because the distance between the fibula and the tibia is also too wide (blue arrow).
However the other ankle also has a rupture of the medial collateral band and anterior and posterior syndesmosis and is unstable.
As the bony structures show a normal alignment, it is almost impossible to see that this ankle is also unstable.
The algoritm will help you to understand why even this ankle is unstable and we'll show this ankle later on.
Video demonstration of algoritm
This video is a demonstration of how the algoritm works.
The first question is: is it a Weber A or B or can this be a Weber C. Once you have answered this question, you have to determine the stage. The algoritm tells you where to look as these injuries all follow a fixed order.
In this case there are four fractures, which can be detected by using the algoritm.
We use the Weber classification as the main classification in the algoritm because of its simplicity and because everybody is familiar with it.
However Weber is actually a simplified copy of the Lauge-Hansen classification.
Lauge-Hansen had already described these three fracture-types and also explained the trauma-mechanism. This is based on the position of the foot in combination with a force applied by the foot, either supination adduction (SA), supination exorotation (SE) or pronation with exorotation (PE).
And he added the stages of these fractures which determine whether the fracture is stable or unstable.
This is why we use Weber for its simplicity but sometimes need to consult Lauge-Hansen for the stages.
Step 1 - is it a Weber A
This step is very easy, because you will always see an avulaion of the lateral malleolus like in this case.
Here another example.
Again very easy.
The avulsion fragment is larger.
This is a stage 1 stable fracture.
This case is more challenging.
This fibula fracture is at the level of the syndesmosis and maybe some people would caal this a Weber B fracture, but it doesn't look like a Weber B.
In the Lauge-Hansen classification this is an avulsion of the lateral malleolus (stage 1) as a result of the supination position of the foot and a push-off fracture of the medial malleolus (stage 2) as a result of an adduction force applied by the foot.
Lauge Hansen calls this supination adduction stage 2 or SA 2.
Just by looking at the images, you can understand the trauma mechanism.
You could call this an unstable bimalleolar Weber A fracture.
On the far left another example of an unstable bimalleolar fracture stage 2 Weber A.
This vertical push off fracture of the medial malleolus is not that common, but can sometimes also be seen when there is only a rupture of the lateral collateral bands like in the case next to it.
Lauge Hansen calls the lateral band rupture also stage 1 of a supination adduction injury, because for the stability of the ankle it doesn't matter whether it is a rupture or an avulsion.
This means that seeing this vertical fracture of the medial malleolus (arrow) always implies an unstable ankle joint because the ring of stability is broken in two places (scroll).
This trauma mechanism always follows this strict order, first stage 1 and then stage 2.
In Weber A when you only see a fibula fracture this is stage 1 and is stable.
If there is a vertical fracture of the medial malleolus this is always stage 2 and is unstable, whether you see a fracture of the lateral malleolus or not.
Step 2 - is it a Weber B
If it is not a Weber A fracture, then the next question is: is it a Weber B?
When you see a Weber B fracture, which is always good visible on either the AP- or the lateral view, the only thing you need to check is whether there is an unstable stage 3 with posterior injury or even stage 4 with medial injury.
The injuries follow a fixed order going from lateral - rupture of anterior syndesmosis or avulsion (stage 1) with an oblique fibula fracture (stage 2) to stage 3 and 4.
Finding stage 4 in a Weber B fracture means that there already is stage 1, 2 and 3.
Weber B is the most common ankle fracture accounting for 60-70% of all ankle fractures.
Just like a Weber C fracture it is the result of an exorotation force applied by the foot.
The only difference is that in Weber B the foot is in supination and the injury starts on the lateral side where the tension is, while in Weber C the injury starts on the medial side due to the position of the foot in pronation.
Scroll through the images to see how the injury follows a clockwise fixed order.
Things become very easy once you remember the fixed order of the injuries:
Tension in anterior syndesmosis results in rupture of the syndesmosis or avulsion of the tibial attachment - Tillaux fracture.
Exorotational force on the fibula results in an oblique - push off fracture.
As the talus pushes the fibula fragment in a posterior direction, the tension in the posterior syndesmosis will result in band rupture or avulsion of the malleolus tertius.
As the talus moves further away in a posterolateral direction, this will create enormous tension in the medial collateral band resulting in a band rupture or avulsion of the medial malleolus.
This fracture mechanism can stop at any stage. Most commonly we see stage 2 which is the oblique fibula fracture, but sometimes the injury stops at stage 1.
Usually this is a rupture of the anterior syndesmosis and we don't see anything on the x-rays, but the patient will have a lot of pain on this specific anterolateral spot.
On the images we see the less common Tillaux fracture as stage 1. No other fracture was seen.
Study these images. You may have to click on them to get a larger view.
First Question: Is it a Weber A, B or could it be a Weber C? Then try to figure out the stage and determine whether the ankle is stable or unstable.
You can look at the next images for an explanation.
Scroll through the images.
It is a stage 4 Weber B fracture, which is unstable.
Step 3 - Could it be a Weber C
If it is not a Weber A or B, then the last question is: could it be a Weber C with a high fibula fracture.
This is an important question, because the fibula fracture in Weber C is most commonly not visible on the x-rays of the ankle and you may have to add additional radiographs of the whole lower leg.
A Weber C fracture is unstable as the fibula fracture is already stage 3 and you wanna look for the other stages 1, 2 and 4, that can be a clue to the high fibula fracture.
Mechanism of Weber C
The mechanism of a Weber C is a result of a position of the foot in pronation with an exorotation force applied by the foot:
- Due to the pronation there is enormous stress on the medial collateral bands and that’s where the injury will start with either a band rupture or an avulsion of the medial malleolus (stage 1).
- As the exorotation force continues the anterior syndesmosis will rupture.
- As a result of the pronation of the foot, the bands on the lateral side are all without any tension. As the exorotation of the foot continues the distal fibula follows this exorotation movement, while the proximal fibula is held in position at the proximal tibiofibular joint and you get a twist-like fracture somewhere above the level of the syndesmosis (stage 3).
- And finally in stage 4 there will be a rupture of the posterior syndesmosis or tertius avulsion (stage 4).
In the axial plane you can see that the injury starts on the medial side due to the pronation of the foot and follows a clockwise rotation through anterior and lateral to posterior.
And just like in a Weber B, you can get injury to the anterior syndesmosis, fibula and finally the posterior syndesmosis.
The two differences between Weber B and C are:
- Weber B starts anterolateral due to the supination of the foot, while Weber C starts on the medial side.
- Exorotation of the foot in Weber B results in a oblique push-off fracture because the fibula is held against the talus due to the supination, while in Weber C the fibula is quite loose resulting in a twist-like high fibula fracture.
Sometimes we are lucky, because the fibula fracture is visible on the x-rays of the ankle.
In many cases however, the fibula fracture is higher up and we need additional x-rays to find the fracture.
It is our job as radiologists to find clues on the x-rays of the ankle that will lead us to these high fibula fractures and the algoritm will help us.
Algoritm in Weber C
When the x-rays of the ankle show no obvious fracture like a Weber A or B, then the question is: could this be a Weber C fracture?
Since the fibula fracture is already stage 3, we wanna look for:
- stage 1 which is the medial injury, where it all starts.
- stage 2 is injury to the anterior syndesmosis, which is usually not visible, unless there is a Tillaux fracture.
- stage 4 is injury to the posterior syndesmosis, which sometimes can not be seen, but will be suspected if there is a widening of the ankle fork or when there is an avulsion of the malleolus tertius like we see in the illustration.
In the next case we'll show you how this algoritm works.
- At first sight it just looks like only a tertius fracture.
- When we look at the algoritm, you can see, that a tertius can be found in a Weber B fracture in stage 3 and in a Weber C fracture in stage 4.
Since this patient doesn't have a Weber B, it must be a Weber C fracture. An isolated tertius fracture is very uncommon and probably does not exist.
- Now we recognize the soft tissue swelling on the medial side, which is stage 1.
- On the enlarge view we also recognize the small avulsion fracture.
Having detected stage 1 and 4 of a Weber C type of trauma mechanism, we now are sure that there must also be a stage 3, which is a high fibula fracture.
The Algoritm in Daily Practise
Examine this case and ask yourself these questions:
- Is it a Weber A, B or can it be a Weber C?
- Once you have answered that question, then the next question is: what is the stage and is it stable or unstable?
Although on the AP-view you might get the impression that it is a Weber A fracture, the lateral view clearly shows an oblique Weber b type fracture, which is stage 2.
There already must be stage 1 and we wanna look for stage 3 and 4 because these are unstable.
Continue with the next illustration.
Stage 3 is injury to the posterior syndesmosis, which is not always visible, but is definitely present, when there is a widening of thw ankle fork or when there is an avulsion of the malleolus tertius as in this case.
Stage 4 is medial injury.
How to explain the exorotation force
Both a Weber B and C fracture are the result of an exorotation force applied by the foot, but it is not the foot that actually moves in exorotation.
The foot is stuck on the ground in supination (Weber B) or pronation (Weber C) and the lower leg - especially the tibia - moves in endorotation and moves forward as a result of the forward motion.
In the illustrations of the stages of a Weber B fracture you can appreciate, that when the tibia endorotates and moves forward, there is an exorotational force applied by the talus upon the fibula.
But for us it is easier to understand the injury mechanism, if we think of an exorotation movement of the foot with posterior displacement.