Peroneal Tendonitis: What Causes It and How Do You Find the Real Problem?
Peroneal tendonitis is inflammation of the peroneal tendons, which 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, such as altered leg or foot alignment, is missed by standard imaging that only looks at the ankle in isolation.
Key takeaways
- Peroneal tendonitis causes pain, swelling and tenderness along the outer ankle.
- It often recurs because alignment problems higher up the leg go undetected.
- Lying-down scans relax the muscles and can hide weight-bearing alignment issues.
- 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 on each leg. They start in the muscles of your outer calf, travel 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 stabilise your ankle 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, walkers on uneven ground, and anyone whose foot or leg alignment places 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 gradually rather than starting suddenly.
Pain usually eases with rest and returns when you increase activity. If you notice sudden weakness, numbness in your foot, or an inability to bear weight, seek urgent medical attention from your GP, 111 or A&E, as these could signal a more serious injury.
What causes peroneal tendonitis?
Peroneal tendonitis is caused by repetitive 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 your hip sits slightly higher on one side, or your knee angles inward, the forces change all the way down to the ankle. The peroneal tendons may be doing extra work to compensate for an alignment issue 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, and builds up gradually rather than happening in one moment.
The two can feel similar because they both cause outer ankle pain. A sprain is usually linked to one specific incident and may involve bruising, while peroneal tendonitis creeps in over days or weeks. They can also coexist. A previous sprain that weakened the ankle can lead to tendonitis later, because the peroneal tendons have to compensate for lost stability.
If your outer ankle pain started without an obvious injury and worsens 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 under real weight-bearing load, showing how your joints actually line up when gravity is acting on them. Lying-down scans relax your muscles and let your joints settle into a neutral position, which can hide the very alignment problems that overload your peroneal tendons during daily life.
A standard ankle X-ray or MRI focuses on the ankle alone. It may show tendon inflammation, but it will not reveal 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 identify where the real source of strain is.
Want to understand whether your ankle pain is connected 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 complement each other well.
What helps peroneal tendonitis recover?
Most cases of peroneal tendonitis improve with conservative measures. Relative rest, reducing the activity that triggered it while staying gently active, is usually the first step. Ice, supportive footwear and a structured exercise programme prescribed 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 address calf tightness, balance work and gradual return to activity.
Recovery time varies from person to person and depends on severity, how long the problem has been present and whether there is an underlying alignment issue driving it. If your peroneal tendonitis keeps coming back despite doing the right exercises, that is a strong signal that something further up the chain may need investigating.
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 appropriate exercises. Persistent cases, especially those driven by an underlying alignment issue, can take longer and may recur until the root cause is addressed.
In most cases, gentle activity and specific strengthening exercises are encouraged. Avoid movements that worsen your pain. A physiotherapist can design a programme that supports recovery without aggravating the tendons.
No. A sprain damages the ligaments, usually from a sudden twist. Peroneal tendonitis is inflammation of the tendons and builds up gradually. They can feel similar, and a previous sprain can make tendonitis more likely.
Recurrence is common when the underlying cause has not been addressed. This could be foot shape, ankle instability from an old injury, or an alignment issue in the knee, hip or pelvis that shifts load onto the outer ankle.
An EOS scan images your full skeleton while you stand, showing how your feet, ankles, knees, hips and spine align under real load. This helps identify 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 self-refer. The process starts with a free video consultation where a specialist radiographer discusses your situation and confirms whether an EOS scan is appropriate for you.
Pricing details are available on 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, with 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.