Peroneal tendonitis

Peroneal tendonitis is inflammation or irritation of the tendons that run along the outside of your ankle and foot. It can cause pain when walking, running or turning your foot, and it may make daily activities more challenging if left untreated. With the right care, most people find relief and return to moving comfortably.

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Close-up of a human ankle with visible muscles and ligaments, highlighting an area of pain.

Anatomy of the ankle

The peroneal tendons run along the outside of your ankle, behind the bony bump known as the outer ankle bone. They help stabilize your foot and turn it outward during movement, which is important for balance whether you're walking on uneven ground or pushing off during a run.

Repeated strain or overuse can cause inflammation, friction and tiny tears in these tendons, especially behind the ankle bone. Without support, this irritation can worsen over time, leading to weakness and ankle instability.

Overview

Symptoms

You may have peroneal tendonitis if you notice:

Pain or tenderness along the outer ankle or side of the foot, especially with activity
Swelling or warmth behind the ankle bone
Weakness or instability when moving or turning the foot
A clicking or snapping sensation along the tendon

Symptoms often develop gradually and may make walking or other activities feel less stable. Getting care early can help protect your ankle and keep you moving comfortably.

Causes

Peroneal tendonitis is most often caused by repeated strain or overuse of the tendons along the outside of the ankle. This can happen through:

Repetitive activities that stress the outer ankle, such as running or walking on uneven surfaces
Sudden increases in activity level or training intensity
Improper or worn footwear that doesn't support the foot
Underlying foot conditions, such as flat feet, that place extra strain on the tendons

Risk factors

Certain factors may increase your risk of developing peroneal tendonitis, though having one or more does not mean you will develop the condition:

A history of ankle sprains or instability
Flat feet or other foot alignment issues
Diabetes or other conditions that affect circulation and healing
Participation in sports or activities that involve repetitive ankle movement
Unsupportive or improperly fitted footwear

Diagnosis

Your foot and ankle specialist will review your symptoms, daily activities, work routine and footwear, then examine your ankle to identify exactly where and when it hurts. Your visit may include a careful exam that tests tendon strength, stability and tenderness along the outer ankle, along with on-site ultrasound or X-rays to view the tendons and rule out tears, fractures or other causes.

Your specialist may also review other conditions, such as ankle instability, flat feet or diabetes, that could be contributing to your symptoms.

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