Peroneal Tendonitis

The peroneal tendons are those that run on the outside of the ankle just behind the bone called the fibula. 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.

Tendonitis is perhaps not the most appropriate term. This word implies that there is inflammation in the tendon. The reality is that there is tendinosis, which means that there is enlargement and thickening with swelling of the tendon. This usually occurs in the setting of overuse, meaning a patient or athlete doing a repetitive activity which irritates or inflames the tendon over long periods of time.​

Symptoms and Clinical Presentation

The history is very important in the setting of peroneal tendinosis. As noted above, these are overuse injuries. People having peroneal tendinosis typically have either tried a new exercise or have markedly increased their activities. Characteristic activities include marathon running or others which require repetitive use of the ankle. Patients will usually present with pain right around the back of the ankle. There is usually no history of a specific injury.

Cause (including risk factors)

​As discussed above, improper training or rapid increases in training and poor footwear can lead to peroneal tendinosis. Also, patients who have a hindfoot varus posture may be more susceptible. This is because in those patients, the heel is slightly turned inwards which requires that the peroneal tendons work harder. Their main job is to evert or turn the ankle to the outside, which fights against the varus position. The harder the tendons work, the more likely they are to develop tendinosis.


​There are two peroneal tendons that run along the back of the fibula. The first is called the peroneus brevis. The term "brevis" implies short. It is called this because it has a shorter muscle and starts lower in the leg. It then runs down around the back of the bone called the fibula on the outside of the leg and inserts, or connects, to the fifth metatarsal. This is in the side of the foot. 

The peroneus longus takes its name because it has a longer course. It starts higher on the leg and runs all the way underneath the foot to insert or connect on the first metatarsal on the other side. Both tendons, however, share the major job of everting or turning the ankle to the outside. The tendons are held in a groove behind the back of the fibula and have a roof made of ligamentous-type tissue over the top of them called a “retinaculum.”


​The diagnosis of peroneal tendinosis can be made in large part by history (the story a patient tells). As noted above, patients will have an overuse activity, rapid increase in recent activity, or other training errors and will have pain in the back and outside of the ankle. There is pain on exam to palpation right on the peroneal tendons. It is important to distinguish this from pain over the fibula which might indicate a different problem, such as stress reaction of the bone. Pain on the fibula occurs directly over the bone which is easily palpated. 

Pain in the peroneals occurs slightly further behind. There is also pain with inversion or carrying the ankle to the outside. Patients may also have weakness in trying to bring the ankle to the outside (in eversion). It is important to look for the varus posturing of the heel which, as noted above, means that the heel is turned inwards. This can predispose a patient to the problem.  

The workup can also include using radiology. X-rays will typically be normal. Ultrasound is a very effective and relatively inexpensive way to assess the tendons and can show an abnormal appearance or tear which sometimes occurs. An MRI is also equally important and can also show a tear.

*Source:  American Orthopaedic Foot & Ankle Society®