Pain on the outside of the ankle is commonly blamed on “peroneal tendonitis”. But in many cases the more important question is not simply why the tendon hurts, but why it is being overloaded in the first place.
The peroneal tendons run behind the prominent bone on the outside of the ankle and help control and stabilise the foot during walking, running and sport. Problems can range from irritation around the tendon to tendon degeneration, a split tear or instability of the tendon behind the ankle bone.
Previous ankle sprains, subtle ankle instability, foot shape and changes in activity can all contribute.
Below I answer the questions I am most commonly asked about pain affecting the peroneal tendons and explain how I approach finding the underlying cause.
Why does the outside of my ankle hurt?
Pain on the outside of the ankle can really be broken down into two main types.
There is the obvious pain that occurs after you have injured or sprained your ankle – traumatic pain.
But there is also pain that comes on more insidiously and can seem almost spontaneous. This type of pain is often related to the tendons running around the outside of the ankle – the peroneal tendons.
A classic symptom of tendon pain is “start-up pain”. The ankle hurts when you first get out of bed in the morning, or get out of the car after a longer journey, and start walking. It will often “get going” and improve as you move, only to become painful again later in the day or evening.
This is commonly called peroneal tendonitis, although peroneal tendinopathy is often the more accurate term. The problem can range from irritation around an otherwise intact tendon, through thickening and degeneration of the tendon itself, to a longitudinal split or tear.
In my experience, the important question is not simply:
“Why does the tendon hurt?”
but:
“Why is this tendon being overloaded?”
A common underlying cause is longstanding instability of the ankle following an ankle sprain. That sprain may have happened recently – or sometimes many years previously
Why can an old ankle ligament sprain cause tendon pain years later?
The ligaments around the outside of the ankle are strong, relatively inelastic structures that help guide the bones of the ankle so that they move in a coordinated way.
Following a sprain, these ligament fibres can be stretched or torn. Even when they heal, they may heal slightly longer or looser than they were originally, subtly changing the way the ankle moves and is stabilised.
The bones of the foot and ankle need to move together in a coordinated fashion, a little like the small cogs inside a watch.
A simple way of picturing what can happen to a ligament is to think of a stick of chewing gum. Before it is stretched, it has a defined length and shape. Once stretched, it may not return completely to its original dimensions. A ligament is obviously far more complex than chewing gum, but the analogy helps explain how an ankle can heal after a sprain yet still remain slightly looser than it was before.
The peroneal tendons then have to become more active stabilisers of the ankle. I sometimes describe them as being rather like puppet strings, constantly pulling and adjusting to help keep the ankle stable.
That extra work can eventually overload the tendons.
This is why simply treating the painful tendon without considering the stability of the ankle can sometimes miss the underlying problem.
Can the shape of my foot cause peroneal tendon pain?
Yes. Not all peroneal tendon problems are caused by an old ankle sprain.
Some people naturally stand and walk with more weight towards the outside of the foot. This is particularly seen in a higher-arched foot, sometimes associated with an inward-tilting heel – a shape we refer to medically as a cavovarus foot.
In this situation, the peroneal tendons have to work harder to control the foot and resist it rolling outwards.
Over many thousands of steps, that can be enough to overload the tendons.
Foot shape and previous ligament injury can also occur together. A foot that naturally tends to roll outwards may be more vulnerable to ankle sprains, and repeated sprains can then make the ankle progressively less stable.
This is another reason why I think it is important to assess the whole foot and ankle, rather than simply looking at the painful tendon on an MRI scan.
What are the peroneal tendons?
There are two main peroneal tendons running down the outside of the ankle – Peroneus Longus and Peroneus Brevis.
They pass behind the prominent outer ankle bone – the end of the fibula – before continuing into the foot.
At this point, the outer ankle bone acts rather like a pulley around which the tendons turn. The tendons are held within a short tunnel by strong retaining tissue that prevents them from moving out of position.
Importantly, the tendons do not simply glide around a fixed pulley. Their tension also acts upon the fibula itself at different stages of walking.
I therefore think of this as a mobile pulley system – part of a dynamic relationship between tendon, bone, ligament and movement.
The peroneal tendons have several roles. They help control the foot, contribute to movement and dynamically stabilise the ankle during walking and running.
They are therefore doing considerably more than simply sliding backwards and forwards.
Why does my pain sometimes start only after I have been exercising for a while?
This is a slightly different pattern of outer ankle pain and one that I think is particularly interesting.
Some people are comfortable when they initially start walking or running but develop pain later during exercise. The discomfort may begin behind the outside ankle bone and then spread upwards along the outside of the calf.
One possible explanation is that the muscle attached to the peroneal tendon is being compressed as it enters the relatively confined tunnel behind the ankle.
If the ankle is unstable, the peroneal muscles have to work harder. Like any muscle that is exercised, they can become larger.
Think of what happens to your biceps if you repeatedly train them at the gym.
In some people, muscle tissue extends relatively low down towards the ankle. As the muscle works during exercise it expands, but it has relatively little space available within the tunnel behind the fibula.
The result can be a cramp-like pain that appears during exercise and can radiate upwards along the outer side of the calf.
Why has the outside of my ankle suddenly started hurting now?
This is a very good question, particularly if you haven’t recently injured your ankle.
I tend to start by asking:
“What has changed?”
It might be:
• a change in shoes;
• increasing your walking or running distance;
• increasing the intensity of exercise;
• a change in terrain;
• weight gain;
• returning to exercise after a period of relative inactivity.
Occasionally there may be other factors, including certain medications or an underlying inflammatory condition.
If tendon problems are occurring in several different parts of the body rather than just one ankle, it is particularly important to consider whether there is a wider cause.
Conversely, tendonitis affecting only one ankle often makes me look more carefully for a local mechanical problem, including the consequences of an old ankle injury.
Can peroneal tendonitis cause swelling behind the ankle bone?
Yes.
The peroneal tendons run within a tendon sheath as they pass behind the fibula. Irritation can produce increased fluid and inflammation around the tendon – known as tenosynovitis.
The tendon itself can also become thickened through degeneration or because a split has developed within it.
This can produce visible or palpable swelling behind and sometimes just below the outer ankle bone.
Swelling does not necessarily mean that the tendon has torn, but persistent swelling associated with pain is one reason I would consider investigating the tendon further.
Why does my ankle click or snap on the outside?
A feeling of clicking or snapping behind the outer ankle bone is slightly different from straightforward tendonitis.
The peroneal tendons normally sit securely in a groove behind the fibula. They are held there by a strong band of tissue called the superior peroneal retinaculum.
This retaining tissue can itself be stretched or torn during an ankle injury. If it no longer holds the tendons securely in their groove, one or both tendons can move abnormally and sometimes flick forwards over the edge of the fibula before moving back again.
This is known as peroneal tendon instability or subluxation.
Some people can actually feel – and occasionally see – the tendon moving when they rotate their ankle.
A repeatedly snapping tendon is worth assessing because the abnormal movement can irritate and potentially damage the tendon over time.
What should I do about pain on the outside of my ankle?
The first thing I would do is think carefully about what changed in the period before the pain started.
Ankle sprains are amongst the commonest injuries we experience, so also ask yourself whether you have previously injured that ankle – even if it was a long time ago.
Then consider what happens if you make the ankle more stable.
Something as simple as trying a small ankle brace can sometimes be informative.
If the ankle immediately feels more secure and, more importantly, your pain disappears or takes much longer to develop, that provides a useful clue that ankle stability may be contributing to the tendon problem.
For people with typical start-up pain, I suggest putting the brace on before taking even the first steps of the day, rather than waiting until the ankle has already become painful.
Try it consistently for around 7–10 days.
The other useful observation is what happens when you stop wearing it. If the symptoms settle while the ankle is supported and then return when the brace is removed, that again suggests that the underlying mechanics and stability of the ankle may be important.
The aim is to understand and treat the cause of the tendon overload, rather than simply treating the painful tendon.
Can I run or exercise with peroneal tendonitis?
Not necessarily – having tendon pain does not automatically mean you have to stop exercising completely.
As a general principle, I prefer people to remain active within the limits of their symptoms rather than stopping all activity automatically.
My simple rule is:
“Do what doesn’t hurt – and if it doesn’t hurt, do it.”
Repeatedly exercising through increasing tendon pain is unlikely to help. However, if you can modify an activity so that it does not hurt, it may be perfectly reasonable to continue.
That might mean reducing distance, speed or hills temporarily. For some people, it means they can maintain surprisingly high levels of activity simply by supporting the ankle temporarily with a brace.
The aim is then to gradually rebuild what the ankle can tolerate unsupported, rather than repeatedly irritating the tendon.
How long does peroneal tendonitis take to settle?
There isn’t one answer because “peroneal tendonitis” describes the painful tendon rather than necessarily telling us why it is painful.
A relatively simple overload problem that has followed a sudden increase in exercise may settle quite quickly once the provoking activity is adjusted.
If, however, the tendon is being repeatedly overloaded because the ankle is unstable, the foot shape is contributing, the tendon is being compressed behind the fibula or there is a structural split within it, the symptoms may continue until that underlying problem is addressed.
This is why I am cautious about simply telling somebody that tendonitis will take a certain number of weeks to recover.
If it is not progressively improving, the more useful question becomes:
“Why isn’t it settling?”
Who should I see about pain on the outside of my ankle?
The foot and ankle is a complex mechanical structure, and getting the diagnosis right is important.
A foot and ankle orthopaedic surgeon, physiotherapist with an interest in foot and ankle problems or podiatrist can assess not just the painful area, but how the whole foot and ankle is functioning.
This may include looking at:
• the stability of the ankle;
• previous ligament injury;
• foot shape and alignment;
• how the foot strikes the ground;
• muscle strength;
• balance and proprioception;
• the precise location of the tenderness;
• whether the peroneal tendons are stable behind the fibula.
Scans can then be arranged when they are likely to add useful information.
What will a physiotherapist or foot and ankle specialist do?
The key is to look for the cause rather than simply treating the site of pain.
The ankle should be examined thoroughly before deciding whether imaging is necessary.
Initial treatment may include activity modification, an ankle brace and a structured physiotherapy programme.
Physiotherapy often includes proprioceptive rehabilitation. This essentially means retraining the balance and neuromuscular control of the ankle so that the muscles around it work efficiently together.
Strengthening the peroneal muscles may also be useful, but this needs to be considered in the context of why the tendon became overloaded in the first place.
If there is significant underlying ankle instability, simply making an already overworked muscle work harder is not necessarily the whole answer.
Can peroneal tendonitis be treated without surgery?
Yes. Most patients with peroneal tendon pain do not automatically require an operation.
Treatment depends upon the underlying cause and may include:
• adjusting the activity that has triggered the problem;
• temporary ankle bracing;
• physiotherapy;
• improving balance and proprioception;
• appropriate strengthening;
• addressing footwear or foot mechanics where relevant;
• gradually rebuilding walking, running or sporting activity.
The aim is not simply to make the tendon less painful. It is to reduce the reason why it is being overloaded.
Surgery is generally considered when there is a significant structural problem – such as a symptomatic split tear, tendon instability or substantial ankle instability – and symptoms have not responded adequately to appropriate non-operative treatment.
Do I need an MRI scan for peroneal tendon pain?
Not everyone with pain on the outside of the ankle needs an immediate scan.
If there has not been a significant injury and the symptoms are typical of a tendon problem, recognising what has triggered the symptoms and making some simple changes may be enough initially.
However, imaging becomes more useful when symptoms persist, the diagnosis is uncertain or there is concern about structural damage to the tendon.
An ultrasound scan can be particularly useful because the tendons can be examined while they move. This can be especially helpful if the problem is clicking, snapping or suspected tendon instability.
An MRI scan provides more detailed information about the tendons, ligaments and other structures within the ankle and can identify significant degeneration or a split tear.
An X-ray does not show the tendon itself particularly well but can be useful for assessing the bones, the alignment and shape of the foot and ankle, and other potential causes of pain.
The scan is therefore part of making the diagnosis – it isn’t the diagnosis by itself.
When should I seek professional advice sooner?
I would recommend assessment sooner if:
• the pain followed a significant injury;
• you cannot comfortably bear weight;
• there is marked swelling or bruising;
• you feel the tendon snapping or moving around the outside ankle bone;
• the ankle repeatedly gives way;
• there is very focal tenderness directly over the bone;
• the pain occurs at rest or wakes you at night;
• the symptoms are progressively worsening;
• the problem simply isn’t improving despite modifying your activity.
Pain that is present continuously rather than being related to movement or loading makes me think more carefully about alternative diagnoses.
A stress fracture, for example, can cause outer foot or ankle pain. These symptoms often become progressively worse with activity and there may be very localised tenderness when pressing directly over the affected bone.
Can getting older contribute to tendon problems?
Potentially, yes.
One factor that is increasingly recognised is sarcopenia – the gradual loss of muscle mass and strength that occurs as we get older, particularly if our activity levels also decrease.
If the muscles controlling the foot and ankle become weaker, the way loads are transmitted through their tendons may change.
Ageing also affects tendon structure itself. The tendon may become less able to tolerate repeated loading and can gradually become painful or degenerate.
This doesn’t mean tendon pain is simply an inevitable consequence of getting older. It does mean that maintaining strength, balance and regular activity becomes increasingly important.
What actually is tendonitis?
In this situation, tendonitis is actually a slightly misleading name.
The ending “-itis” implies inflammation – in the way we think of appendicitis or tonsillitis.
Most longstanding tendon problems are not simply an acutely inflamed tendon.
Instead, repeated loading can produce microscopic damage within the tendon fibres. If the tendon does not get an opportunity to repair itself adequately before it is repeatedly loaded again, its structure can gradually deteriorate.
The tendon may become thickened and painful and, in more advanced cases, a split can develop within it.
There can certainly be inflammation around the tendon – known as tenosynovitis or synovitis – but the tendon itself is often better described as degenerative rather than simply inflamed.
That is why the term tendinopathy is increasingly used.
What is a split tear of the peroneal tendon?
The easiest way to imagine a tendon is to think of a ponytail.
A tendon is made from many parallel fibres bundled together.
A split tear doesn’t usually mean that the tendon has been completely cut across, as though somebody had taken scissors to the ponytail.
Instead, the tear tends to run lengthways between the fibres.
Imagine separating the hairs of the ponytail longitudinally before starting to plait them. That is much closer to what a peroneal split tear can look like.
Can a peroneal tendon split heal by itself?
Small tendon abnormalities seen on scans do not automatically require surgery, particularly if they are not causing significant symptoms.
However, a substantial symptomatic split tear may struggle to heal completely while the tendon continues to experience the same abnormal mechanical stresses that caused the damage in the first place.
This is why the scan finding should never really be considered in isolation.
The important questions are:
Does the tear correspond with the patient’s pain?
and:
Why did the tendon split?
If symptoms persist despite appropriate non-operative treatment, surgery may be considered.
Can a split peroneal tendon be repaired?
Yes.
The exact operation depends upon what is found in the tendon.
The tendon is exposed and unhealthy or badly damaged tissue can be removed – a process called debridement.
If there is a repairable longitudinal split, the tendon can often be sutured back together.
Sometimes a damaged section is excised, leaving a slightly smaller but healthier tendon.
In more severe cases, one tendon may be too badly damaged, shredded or swollen to function normally. The severely damaged section can then be removed and the affected tendon joined to the neighbouring peroneal tendon – a procedure called tenodesis.
Because the two peroneal tendons have overlapping functions, this can provide good pain relief and useful function.
If I need tendon surgery, should the ankle ligaments be treated as well?
This is, in my opinion, one of the most important questions.
Peroneal tendons don’t usually split for no reason.
If I am operating on a damaged peroneal tendon, I want to understand what caused that damage.
If longstanding ankle instability has repeatedly overloaded the tendon, simply repairing the tendon without addressing the instability risks treating the consequence rather than the cause.
For this reason, assessment of the lateral ankle ligaments is an important part of planning peroneal tendon surgery.
Where significant instability is present, tightening or reconstructing the ankle ligaments may be considered at the same operation.
Similarly, excess muscle within the tendon tunnel, inflammation around the tendon, tendon instability or other mechanical causes of compression may need to be addressed.
The objective is not simply to make a damaged tendon look better.
It is to create an environment in which that tendon can work normally again.
The important point throughout is to identify why the tendon has become painful, rather than treating “tendonitis” as though it were a diagnosis in itself.
Persistent pain on the outside of your ankle?
If pain around the outside of your ankle is continuing despite modifying your activity, or you have recurrent ankle instability, swelling, clicking or snapping around the peroneal tendons, a specialist assessment can help establish why the tendon is being overloaded and whether further investigation is appropriate.
About the author
This information has been written and reviewed by Mr Tim Williams, Consultant Orthopaedic Foot and Ankle Surgeon.
Mr Williams specialises in the assessment and treatment of foot and ankle conditions including ankle instability, peroneal tendon disorders and tendon tears.
Last reviewed: August 2026
