Anatomy of the lateral ankle sprain injuries [2021].

This is probably one of the most common lower limb injuries seen in the clinic and also one of the post poorly self managed injuries we see.

What seems like a relatively simple injury can cause a lot of trouble further down the line if not managed well.

Before we even start here’s an interesting fact:

Ankle sprains , the curse of the biped !

Chimps don’t sprain their ankles thanks to their wide base of support, grasping feet, and abducting toes !

There is  NO such thing as a simple ankle sprain.

Most of us have had one at some stage in our lives twisted our ankle on an uneven surface – some many more times than others ! They can range from the mildly irritating simple ligament sprains to torn ligaments and then in worst cast the recurrent unstable ankle or chronic ankle instability ( CAI).

In most ankle sprains the story goes something like this:

we roll our ankle doing sport or out walking on uneven ground , the pain passes, and the ankle seems to feel ok and so we just move on with our lives and forget about it…until we do it again.

This is a common issue and not an unusual pattern that we see.

Statistics vary, but up to 40% of people who suffer a “simple ” ankle sprain go on to suffer repetitive ankle sprains and ongoing symptoms – termed Chronic Ankle Instability (CAI).

The good news is, whether you’ve sprained your ankle once, or whether you have already developed CAI, you can still improve your ankle control and reduce your risk of re-injury in the future.

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How did you sprain your ankle ?

ankle injury diagram | Arana Hills Physiotherapy

Lateral ankle sprains usually occurs when the body’s center of mass  rapidly moves over the landing or weight-bearing foot. This results in the  ankle rolling outward , whilst the foot turns inward causing the lateral ligament to stretch and tear. This mechanism of injury is commonly seen in;

  • Sudden changes of direction.
  • Poor landing mechanics when jumping
  • Landing on an uneven surface or object.
  • Slipping on unstable or slippery surface.

What is injured when we sprain the ankle ?

These mechanisms of these injuries are forced plantar flexion and inversion of the ankle which puts stress through the capsulo-ligamentous structures of the outside of the ankle:

  • Anterior talo fibular ligament, (ATFL).
  • Anterior tibio fibular ligament, ligament between the fibula and tibia.
  • Calcaneo fibular ligament (CFL).
  • Posterior Talo fibular ligament (PTFL).
  • Syndesmosis, The tissue between the fibula and tibia.



The ATFL prevents forward movement of the ankle from the tiba and fibula complex as well as preventing the inversion and internal rotation of the ankle joint.

The strain in the ATFL increases the more you point your foot away from the body, this movement is known as plantar flexion.

It is also the weakest of the three ligaments in the outside of the ankle and this is why it is the most commonly injured ligament in the classic inversion/plantar flexion mechanism.

The CFL restricts excessive supination/rotation of both the ankle and is a stronger structure than the ATFL. It is more commonly injured if the ankle is forcibly inverted when in a neutral to dorsiflexed position.

CFL injuries are usually seen in more significant ankle injuries than simple sprains.

Ankle joint is not so simple

Whilst many people often think of the ankle as existing as simply the hinge joint that moves up and down, ( dorsiflex and plantarflex), the reality is that this is only part of how it operates which is often referred to as the as the  ankle complex.

It contains the:

  • Talocrual joint – between the talus and both the tibia and fibula;
  • Subtalar joint – between the talus and the calcaneus;
  • Inferior tibiofibular joint – at the ‘southern’ end of the tibia and the fibula.

All three areas need to work together to allow the foot to lift (dorsiflex), point (plantarflex) and rotate (supinate and pronate).

Here’s a video to show what the ankle joint involves

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Are there different grades of ankle ligament injury ?

Traditionally ankle injuries were graded as such :

Grade I ankle injury:

  • Incomplete tear of the ATFL,
  • Little swelling or tenderness,
  • Minimal or no functional loss.
  • Some loss of joint movement.
  • No mechanical instability of the joint.

Grade II ankle injury:

  • Complete tear of the ATFL and partial tear of the CFL. ligaments.
  • Moderate pain, swelling, and tenderness over the involved structures.
  • There is some loss of joint movement.
  • Mild to moderate instability.

Grade III ankle injury:

  • Complete rupture of the ATFL and CFL.
  • Marked swelling, hemorrhage, and tenderness.
  • There is loss of function.
  • Abnormal motion and instability of the joint.

Who’s at risk of ankle sprains ?

Apparently not chimpanzees that’s who ! however for us humans  theses factors are important in predicting ankle sprains and also ones we can change;

  • Giving way  or mechanical instability (laxity on testing).
  • Pain and swelling.
  • Loss of strength at the ankle , hip and core.
  • Recurrent sprains.
  • Functional instability (poor performance on balance and proprioception tests).
  • Fear of uneven grounds.
  • Decreasing level of exercise or sport.

Other factors which have been shown to strongly predict an ankle sprain are;

  • younger age.
  • female gender.
  • greater height.
  • low and high BMI.

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What do i do next after an ankle sprain ?

The biggest predictor of an ankle injury is not sufficiently rehabilitating a previous ankle injury !

Management is key , poorly managed ankle sprains have the potential to  lead to further ankle injuries and in around 40% of cases can lead to what is termed chronic ankle instability, ( CAI). However with the right approach you can make a full recovery and we show you how in the next of our ankle rehab series here

If you need help with an ankle injury you can book in to see one of us here



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