The peroneal tendons run along the outer side of your ankle and serve two critical roles: they evert (turn outward) your foot and stabilize your ankle against rolling inward. There are two of them, the peroneus longus and the peroneus brevis, and they work together during every step you take.
Where the Peroneal Tendons Are
Both peroneal tendons originate from the fibula, the thinner bone on the outer side of your lower leg. The peroneus brevis starts from the lower two-thirds of the fibula and travels down behind the bony bump on the outside of your ankle (the lateral malleolus), attaching to the base of your fifth metatarsal, the small bony knob you can feel on the outer edge of your midfoot. The peroneus longus takes a longer path: it crosses under the foot and attaches to bones on the inner side, giving it leverage to press the big-toe side of your foot toward the ground.
As the two tendons pass behind the ankle, they sit inside a groove in the bone and are held in place by a band of tissue called the superior peroneal retinaculum. This band converts the groove into a tunnel, keeping the tendons from slipping out of position during movement.
How They Move Your Foot
The peroneus brevis is the primary evertor of your foot, responsible for about 63% of total eversion power. Eversion is the motion of tilting the sole of your foot outward. You use it constantly without thinking about it, especially when walking on uneven ground or shifting your weight side to side. The peroneus brevis also assists with plantarflexion, the motion of pointing your foot downward.
The peroneus longus has a slightly different job. Because it crosses under the foot to the inner side, it pushes the base of your big toe down toward the ground (plantarflexing the first ray). This stabilizes the inner arch of your foot during the push-off phase of walking and running. It also contributes to eversion, working alongside the brevis.
Their Role in Walking and Running
During a normal walking stride, the peroneal tendons are active through most of the cycle. From the moment your heel hits the ground through midstance, both tendons contract eccentrically, meaning they lengthen under tension to control your foot’s position and prevent it from involuntarily rolling inward. This is especially important on the heel strike, when inversion forces are highest.
From midstance through push-off, the peroneus longus shifts to a concentric contraction, actively shortening to press the first ray down and evert the foot. This locks the arch into a rigid lever for propulsion. Without this action, your push-off would feel weak and unstable, and the inner edge of your foot wouldn’t bear weight properly.
Ankle Stability and Sprain Prevention
The peroneal tendons are often called the dynamic stabilizers of the lateral ankle. While ligaments provide passive stability (holding bones together when you’re still), the peroneals actively fire to resist inversion, the motion that causes the classic “rolled ankle.” When your foot starts to turn inward unexpectedly, the peroneals contract reflexively to pull it back.
This role becomes even more important if your lateral ankle ligaments are damaged. Research shows that when those ligaments are already torn or stretched, the peroneus longus tendon provides a substantial contribution to passive resistance against further spraining. In other words, if your ligaments are compromised, healthy peroneal tendons become your ankle’s main line of defense against giving way.
What Goes Wrong: Common Peroneal Problems
Because these tendons handle so much force, particularly in athletes and people who spend time on uneven surfaces, they’re vulnerable to several injuries.
- Peroneal tendonitis is inflammation of one or both tendons, usually from overuse or a sudden increase in activity. It causes pain and swelling along the outer ankle. Most people recover fully in about a month with rest, ice, and physical therapy. Conservative treatments typically relieve pain and inflammation within three to four weeks.
- Peroneal tendon tears can be partial or complete. The peroneus brevis tears more often because it sits closer to the bone and can get pinched. Symptoms include pain along the outside of the ankle, swelling, and a feeling that the ankle could “give out” while walking, especially on uneven ground. Chronic tears may cause pain that comes and goes rather than constant discomfort.
- Peroneal tendon subluxation happens when the tendons slip out of their groove behind the ankle bone. This occurs when the superior peroneal retinaculum is torn or stretched, often from a sudden dorsiflexion and eversion injury followed by a reflexive contraction of the peroneal muscles. Repeated ankle sprains can leave the retinaculum lax and incompetent, leading to chronic subluxation where the tendons pop in and out repeatedly.
How Peroneal Problems Are Diagnosed
A physical exam is usually the first step. Your provider will move your foot and ankle into different positions, apply gentle resistance as you try to evert your foot, and press on specific areas around the outer ankle to identify the source of pain. Weakness during resisted eversion or pain behind the lateral malleolus points toward a peroneal issue.
When imaging is needed, MRI is the gold standard for detecting peroneal tendon tears. One recent study found MRI had 100% sensitivity and specificity for peroneus brevis tears, though earlier research reported much lower accuracy, with sensitivities ranging from 44% to 56%. Ultrasound is also effective, with 88% sensitivity and 100% specificity for detecting tears, and has the advantage of being dynamic: the examiner can watch the tendons in real time as you move your ankle, which is particularly useful for diagnosing subluxation.
Recovery and Rehabilitation
For tendonitis, the treatment path is straightforward. Rest, icing, and temporary bracing reduce inflammation, while physical therapy rebuilds strength and flexibility. Therapists typically focus on eccentric strengthening exercises, balance training on unstable surfaces, and gradual return to activity. Most people are back to normal in four to six weeks.
Tendon tears and chronic subluxation sometimes require surgery, particularly when conservative treatment fails or the tear is complete. Surgical repair for tears involves stitching the tendon back together or, in severe cases, grafting tissue from one tendon to reinforce the other. For subluxation, the procedure deepens the groove behind the ankle or tightens the retinaculum to keep the tendons in place. Recovery from surgery generally involves a period of immobilization followed by progressive physical therapy over several months.
Regardless of the specific injury, rehabilitation emphasizes restoring the peroneal tendons’ ability to stabilize the ankle dynamically. Balance and proprioception exercises (standing on one leg, using wobble boards) retrain the reflexive firing patterns that protect against future sprains and re-injury.