Peroneal Tendonitis: What Causes It and How Do You Find the Real Problem?
Peroneal tendonitis is inflammation of the peroneal tendons. These run behind the outer ankle bone. It causes pain along the outside of your ankle and foot, especially during activity. It often keeps coming back because the underlying cause is missed. This may be altered leg or foot alignment, which standard imaging misses because it only looks at the ankle on its own.
Key points
- Peroneal tendonitis causes pain, swelling and tenderness along the outer ankle.
- It often comes back because alignment problems higher up the leg are not picked up.
- Scans done lying down relax the muscles and can hide weight-bearing alignment problems.
- A standing whole-body scan shows how your foot, ankle, knee and hip work together under load.
- ScanAlign provides diagnostic imaging only, not treatment.
You have two peroneal tendons in each leg. They start in the muscles of your outer calf. They pass behind the bony bump on the outside of your ankle (the lateral malleolus) and attach to the bones of your foot. Their job is to keep your ankle stable and help you push off when you walk or run.
When these tendons become irritated or inflamed, the condition is called peroneal tendonitis. It is common in runners, in people who walk on uneven ground, and in anyone whose foot or leg alignment puts extra strain on the outer ankle.
What are the symptoms of peroneal tendonitis?
The main symptom is a dull, aching pain along the outside of your ankle, behind or below the bony bump. It usually builds up slowly rather than starting suddenly.
Pain usually eases with rest and returns when you do more. If you notice sudden weakness, numbness in your foot, or you cannot put weight on it, get urgent medical help from your doctor or the nearest emergency department. These could be signs of a more serious injury.
What causes peroneal tendonitis?
Peroneal tendonitis is caused by repeated overload on the peroneal tendons. This can happen because of how you train, the surfaces you move on, or, very commonly, the way your leg and foot are aligned.
Your body is a connected chain from your feet to your head. If one hip sits slightly higher than the other, or your knee angles inward, the forces change all the way down to the ankle. The peroneal tendons may be doing extra work to make up for an alignment problem that started much higher up.
How is peroneal tendonitis different from an ankle sprain?
A lateral ankle sprain damages the ligaments on the outer ankle, usually from a sudden twist or roll. Peroneal tendonitis affects the tendons, not the ligaments. It builds up slowly rather than happening in one moment.
The two can feel alike because both cause outer ankle pain. A sprain is usually linked to one specific incident and may come with bruising. Peroneal tendonitis creeps in over days or weeks. You can also have both. A past sprain that weakened the ankle can lead to tendonitis later, because the peroneal tendons have to make up for the lost stability.
If your outer ankle pain started without a clear injury and gets worse with activity, peroneal tendonitis is worth considering.
Why does standing alignment imaging matter for ankle pain?
Standing alignment imaging matters because it captures your skeleton while it carries your real body weight. It shows how your joints actually line up when gravity is acting on them. Scans done lying down relax your muscles and let your joints settle into a neutral position. This can hide the very alignment problems that overload your peroneal tendons in daily life.
A standard ankle X-ray or MRI looks at the ankle alone. It may show inflammation of the tendon. But it will not show whether the problem started because your knee angle, hip position or pelvic tilt is sending extra force down the outer side of your leg.
An EOS scan captures a full standing image from your feet to your spine in a single low-dose exposure, with about 90% less radiation than a standard X-ray, around ten times less. This lets a specialist see the whole chain and find where the real source of strain is.
Would you like to know whether your ankle pain is linked to a bigger alignment picture?
Book a free video consultationWhen MRI is the better choice: EOS shows bones, joints and alignment. If your clinician suspects a tendon tear, significant soft-tissue damage or nerve involvement, MRI is usually the better tool for those details. The two types of imaging work well together.
What helps peroneal tendonitis recover?
Most cases of peroneal tendonitis improve with conservative measures. Relative rest is usually the first step: cutting back the activity that triggered it while staying gently active. Ice, supportive footwear and a structured exercise programme set by a physiotherapist can help.
Exercises that strengthen the peroneal muscles and improve ankle stability are often a key part of recovery. Your physiotherapist may also work on calf tightness, balance and a gradual return to activity.
Recovery time differs from person to person. It depends on how severe the problem is, how long you have had it, and whether an underlying alignment problem is driving it. If your peroneal tendonitis keeps coming back even though you are doing the right exercises, that is a strong sign that something further up the chain may need looking into.
Before you start treatment, or change the one you are on, it is worth getting a detailed diagnosis. Knowing whether the cause sits in the pelvis, the legs or the spine changes what will actually help.
ScanAlign does not provide treatment. We provide the diagnostic imaging that helps your physiotherapist, podiatrist or surgeon understand the full picture. You can learn more about how a whole-body standing EOS scan works on our main page.
Frequently asked questions about peroneal tendonitis
It usually feels like a dull ache or burning along the outside of your ankle, behind the bony bump. The pain often gets worse with activity and eases when you rest.
There is no single timeline. Mild cases may settle within a few weeks with rest and the right exercises. Persistent cases, especially those driven by an underlying alignment problem, can take longer and may come back until the root cause is addressed.
In most cases, gentle activity and specific strengthening exercises are encouraged. Avoid movements that make your pain worse. A physiotherapist can design a programme that supports recovery without irritating the tendons.
No. A sprain damages the ligaments, usually from a sudden twist. Peroneal tendonitis is inflammation of the tendons and builds up slowly. They can feel alike, and a past sprain can make tendonitis more likely.
It commonly comes back when the underlying cause has not been addressed. This could be foot shape, ankle instability from an old injury, or an alignment problem in the knee, hip or pelvis that shifts load onto the outer ankle.
An EOS scan images your full skeleton while you stand. It shows how your feet, ankles, knees, hips and spine line up under real load. This helps find alignment problems further up the chain that may be overloading your peroneal tendons.
Yes. The EOS system uses about 90% less radiation than a standard X-ray, around ten times less. You can find more detail on our FAQs page.
No. You can refer yourself. The process starts with a free video consultation. A specialist radiographer talks through your situation and confirms whether an EOS scan is right for you.
The price for patients travelling from abroad is confirmed during the free video consultation. You can also visit our FAQs and cost page.
They serve different purposes. EOS shows bones, joints and whole-body alignment under load. MRI is better for soft-tissue detail such as tendon tears, swelling inside the tendon sheath, or nerve involvement. Your clinician may recommend one or both, depending on your situation.
Could your ankle pain be an alignment problem?
A free video consultation with a specialist radiographer can help you find out before you decide to travel to London. There is no obligation and no referral needed.
Book a free video consultationSources
- NHS. "Tendonitis." nhs.uk. Accessed 2025.
- Davda K, Malhotra K, O'Donnell P, Singh D. "Peroneal tendon disorders." EFORT Open Reviews, 2(6), 281–292, 2017.
- Illés T, Somoskeöy S. "The EOS imaging system and its uses in daily orthopaedic practice." International Orthopaedics (SICOT), 36(7), 1325–1331, 2012.
Written by Abbas Dhami (Specialist Diagnostic Radiographer)
This page is general information and not a diagnosis.
ScanAlign is the trading name of CoreMed Solutions Ltd and operates under The Harley Street Hospital's CQC licence.