What is peroneal tendinosis?

Peroneal Tendons

The peroneal tendons are on the outside of the ankle just behind the bone called the fibula. Peroneal tendinosis is the name for the enlargement, thickening, and swelling of these tendons. This usually occurs with overuse, such as a repetitive activity that irritates the tendon over long periods of time.


People with peroneal tendinosis typically have tried a new exercise or markedly increased their activities. Characteristic activities include marathon running or others that require repetitive use of the ankle. Patients usually have pain around the back and outside of the ankle. There often is no history of a specific injury.


Improper training or rapid increases in training and poorly fitting shoes can lead to peroneal tendinosis. Also, patients who have high arches may be more susceptible because their heel is turned inwards slightly, which requires the peroneal tendons to work harder to turn the ankle to the outside. The harder the tendons work, the more likely patients are to develop tendinosis.


Tendons connect muscle to bone and allow them to exert their force across the joints that separate bones. Ligaments, on the other hand, connect bone to bone. There are two peroneal tendons that run along the back of the fibula. The first is called the peroneus brevis. It runs down around the back of the bone called the fibula on the outside of the leg and connects to the fifth metatarsal on the side of the foot.

The peroneus longus takes its name because it has a longer course. It runs all the way underneath the foot to connect to the first metatarsal on the other side. Both tendons share the major job of turning the ankle to the outside. The tendons are held in a groove behind the back of the fibula and are covered by a ligament-type tissue called a retinaculum.