Peroneal tendonitis occurs when the peroneal tendons become inflamed. This happens when there is an increased load and overuse of the tendons, leading to them rubbing on the bone.

This friction causes the tendons to swell. Over time, the tendons will thicken in size to try and manage the increased load more efficiently.

This article discusses the causes, symptoms, diagnosis, and treatment of peroneal tendonitis in more detail. It also discusses peroneal tendon anatomy, how to prevent peroneal tendonitis, and the potential outlook for the condition.

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A tendon is a band of tissue that attaches muscle to bone.

There are two peroneal tendons in each leg. They run side by side down the lower leg bone (fibula) and behind the bony lump on the outside of the ankle called the lateral malleolus.

One peroneal tendon attaches to the outside of the foot at the base of the little toe (fifth metatarsal). The other tendon goes underneath the foot and attaches to the inside of the arch.

The peroneal tendons stabilize the ankle when it is bearing weight and protect it from sprains. They also help turn the foot out and stabilize the arch when walking.

The United Kingdom’s National Health Service (NHS) notes that people who take part in a sport that involves repetitive ankle motion are most prone to peroneal tendonitis.

It may be more common in athletes, especially runners, as they are more likely to roll their feet outwards, causing friction between the tendon and bone.

Factors that can contribute to peroneal tendonitis include:

  • overuse
  • a sudden increase in training, particularly weight-bearing activities, such as walking, running, and jumping
  • improper training techniques
  • inadequate or unsupportive footwear
  • previous foot or ankle injuries or surgery
  • weakness in or tightness in the feet and leg muscles
  • smoking
  • obesity
  • diabetes
  • inflammatory conditions, such as rheumatoid arthritis and ankylosing spondylitis
  • prolonged use of oral corticosteroids and fluoroquinolones, which is a family of antibiotics

Over time, the damaged peroneal tendons will thicken as scar tissue tries to repair the damaged area. This makes the tendons weaker and more prone to tearing.

Peroneal tendonitis can either be acute, meaning that it comes on suddenly, or chronic, meaning that it develops over time.

According to the NHS, symptoms may include:

  • pain at the back of the ankle
  • pain that worsens during activity and lessens during rest
  • pain when turning the foot in or out
  • swelling at the back of the ankle
  • instability of the affected ankle when bearing weight
  • the area is warm to the touch

The doctor will first discuss the person’s medical history with them. This will often point to overuse, increased activity, or another cause of peroneal tendonitis.

It is important to determine that the pain is in the peroneal tendons and not the fibula, as this could indicate a different problem.

A physiotherapist or doctor will use a variety of techniques in a physical exam to look for symptoms, generally by moving the foot and ankle into different positions and applying pressure.

They may also order an X-ray, CT, ultrasound, or MRI scan to rule out any breaks, identify abnormal swelling or scar tissue, and further help with diagnosis.

Because overuse of the tendons often causes peroneal tendonitis, rest is crucial to help them heal.

The individual should avoid walking or any other activities that may aggravate the injury until the pain has gone. The area needs time to recover, and the pain will lessen over time.

Steps people can take at home include:

The NHS also notes that wearing comfortable trainers or hiking boots with a slight heel can help support the peroneal tendons.

If peroneal tendonitis does not improve with rest and treatment at home, a doctor may recommend:

However, a healthcare professional will only recommend cortisone injections or surgery in rare cases.

There are several things that people can do to try and avoid getting peroneal tendonitis:

  • Wearing appropriate footwear that properly supports the foot and ankle.
  • Stretching the calf and peroneal muscles. If this is during recovery, the person should wait until signs of inflammation and pain have gone.
  • Increasing training workload gradually.
  • Maintaining a level of activity throughout recovery. This is particularly important for sportspeople during the off-season.

People experiencing peroneal tendinitis will usually make a full recovery, but it will take time. It is essential not to rush back to activities too soon.

The NHS notes that, for most people, symptoms will improve within 3 months of following a healthcare professional’s advice. However, it may take up to a year to improve for others.

People may still experience periods of pain flare-ups during their recovery.

If pain worsens or does not improve with treatment, a person should speak with their doctor. For example, a healthcare professional may recommend different exercises or stretches for someone to try.

If left untreated, peroneal tendonitis can lead to a tear, which may lead to further complications. Therefore, speaking with a healthcare professional as soon as possible is advisable.

Peroneal tendonitis can cause pain and swelling at the back of the ankle.

It occurs due to overuse of the tendons, but other factors can also contribute to its development.

A person may be able to treat the condition at home with steps such as the RICE method, OTC pain medications, and wearing supportive footwear.

People should speak with a healthcare professional if their symptoms do not improve with home treatment.