Your peroneal muscles run along the outer side of your lower leg and become tendons near the ankle, where they pass through an important bone called the lateral malleolus.

These muscles and tendons are responsible for inwardly rolling your ankles and pointing your toe downward. Running can irritate these tendons; understanding their causes and symptoms will enable you to manage any pain effectively and resume running as soon as possible.

Causes

Peroneal muscles run along either side, behind and beneath the fibula bone on the outer side of your lower leg, held in place by ligaments including superior and inferior peroneal retinaculum. Injury to these muscles or tendons may cause them to slip over ankle bone and cause peroneal tendon dislocation which results in pain, swelling and instability of ankle.

These muscles and tendons are more likely to be injured among individuals who spend all day standing, especially those whose jobs involve frequent changes of direction. Athletes who engage in sports that require repeated running and jumping also stand an increased chance of experiencing injuries to these structures.

Overuse can damage peroneal muscles and tendons, causing small injuries that lead to tendinitis – inflammation of the tendons that is sometimes called tendinosis (chronic degeneration of tendon). Both forms can be painful and limit activity levels.

Symptoms

Peroneal muscles are two muscles on the outside of your lower leg that extend from just below your ankle bone and attach into bones in your feet. Of these two, the longer is Peroneus longus while its short counterpart Peroneus brevis. When injured, these two musculatures may become inflamed or painful; hence their name.

Overuse or injury of these muscles causes their tendons (fibrous tissue that connects muscle to bone) to swell up, becoming inflamed or injured and no longer functioning as they should, leading to discomfort and weakness in your ankle or foot. This may result in pain and weakness within both.

Peroneal tendonitis symptoms typically include pain along the outer side of your ankle and up your foot, often worse when pointing your toes or moving your ankle up and down.

Physical therapists can be invaluable allies for treating foot and ankle conditions. They will guide you through a series of exercises designed to build up ankle and leg strength and alleviate pain and mobility issues at home; such as doing lateral calcaneal glides or ankle alphabet exercises which relieve pressure off peroneal tendons to restore normal function and ease symptoms.

Diagnosis

X-rays and MRI scans typically aren’t necessary when diagnosing this condition; rather it is generally diagnosed based on its location and nature of pain. Your doctor will likely gently press on the outside of your foot where you feel the lateral malleolus bone (a bone called the lateral malleolus) as well as where your peroneal tendon muscles contract when you point down (plantar flexion). If tenderness appears in these areas it could indicate injury to either peroneus longus muscle or its tendon.

The peroneus longus muscle arises from the head and proximal two-thirds of the fibula shaft on the outside of your lower leg, where its tendon then passes over your ankle joint and the lateral malleolus before turning under cuboid bone to sit in a groove beneath foot. When your toes point down with any force this muscle contracts creating friction which leads to inflammation and pain.

Treatment

When the peroneus longus muscle tendon becomes irritated or overused due to slight variations in running biomechanics (inversion/plantar flexion), it can result in pain along its entirety. This could either occur immediately as a result of trauma, or develop over time through repeated trauma; swelling and pain along the outside of ankle are symptoms commonly observed.

Your peroneus muscles (peroneus brevis and longus) originate on the lateral side of your leg (outside your ankle). They travel down your fibula until they form tendons around your ankle; one tendon attaches directly to your little toe, while the other runs underneath your foot and connects with an arch on the opposite side of your ankle.

At-risk runners include people with high arches in their feet and repetitive activities such as playing sports, hiking or biking. Treatment includes rest from activities that aggravate the tendon as well as anti-inflammatory medication and physical therapy to decrease swelling, retrain proper ankle movements and strengthen tendons.