Peroneal tendonitis is inflammation of one or both tendons that run along the outer side of your ankle and foot. It causes pain behind and below the outer ankle bone, typically from repetitive stress or overuse. Most people recover fully in about a month with conservative treatment, though certain foot structures and activity patterns can make recurrence more likely if the underlying cause isn’t addressed.
The Tendons Involved
Two tendons make up the peroneal group. The peroneus longus and peroneus brevis are the only muscles in the outer compartment of the lower leg, and they share a tight space as they wrap behind the ankle bone. The brevis originates from the lower two-thirds of the fibula (the thinner bone in your lower leg) and attaches to the base of your fifth metatarsal, the bony bump on the outside edge of your foot. The longus runs underneath the brevis, crosses the sole of the foot, and attaches on the opposite side.
Together, these tendons evert your foot (tilt the sole outward) and help point your toes downward. More importantly for daily life, they stabilize your ankle on uneven ground and prevent it from rolling inward. Every step on a trail, every lateral cut in a sport, and every stumble on a curb activates these tendons. That constant demand is exactly why they’re vulnerable to overuse injuries.
What Causes It
Peroneal tendonitis results from overuse in the vast majority of cases. A sudden increase in training volume, switching to hillier terrain, or ramping up court sports without adequate conditioning are common triggers. The tendons slide through a narrow groove behind the ankle bone, and repetitive friction in that groove creates irritation and swelling.
Certain foot and ankle characteristics raise your risk substantially. A high-arched foot (sometimes called a cavus foot) tilts the heel inward, placing extra tension on the peroneal tendons with every step. This varus hindfoot alignment can lead to inflammation, partial tearing, or the tendons slipping out of their groove. Chronic ankle instability from prior sprains is another major contributor. Loose ligaments allow the tendons to move more than they should around the fibula, stretching the band of tissue that holds them in place. Some people also have an anatomical variation where the muscle belly of the brevis sits lower than normal and gets squeezed as it passes through the narrow tendon sheath.
How It Feels
The hallmark symptom is pain along the outer ankle, specifically behind and just below the bony bump on the outside (the lateral malleolus). The pain tends to come on gradually rather than suddenly. Early on, you might only notice it during or after activity. As the condition progresses, the pain can become constant, with noticeable swelling or warmth along the tendon’s path.
Walking on uneven surfaces, pushing off during a run, or turning your foot outward against resistance will typically reproduce the pain. Some people feel a snapping or popping sensation behind the ankle bone, which can indicate the tendons are slipping in and out of their groove. That’s a related but distinct problem called peroneal subluxation, which involves a forceful contraction of the tendons during sudden ankle movements like landing from a jump.
Tendonitis vs. Tendonosis vs. Subluxation
These three conditions overlap in location but differ in what’s happening inside the tendon. Tendonitis is acute inflammation, usually from a recent spike in activity. The tendon is irritated but structurally intact. Tendonosis, by contrast, is a chronic degenerative change where the tendon’s internal structure has broken down over time. It develops when tendonitis isn’t properly addressed and the tendon never fully heals between bouts of stress. Pain from tendonosis tends to be more persistent and slower to respond to rest.
Subluxation is a mechanical problem. The tendons physically slide out of the groove behind the ankle bone, often during explosive movements. It usually involves damage to the retinaculum, the fibrous band that holds the tendons in place. While tendonitis and tendonosis are overuse injuries, subluxation often starts with a single forceful event.
How It’s Diagnosed
A good clinical history and physical exam are often enough to identify peroneal tendonitis. Your provider will press along the tendons behind the ankle, ask you to evert your foot against resistance, and check for instability. If you’re being seen after an acute ankle injury, the standard approach starts with X-rays to rule out fractures. A specific finding called a “fleck sign” on X-ray, a small chip of bone pulled away from the fibula, suggests the retinaculum was torn and the tendons may be subluxating.
Ultrasound and MRI are used to confirm the diagnosis when the clinical picture is unclear or when a tear is suspected. MRI provides more detailed images of tendon degeneration and surrounding structures, while ultrasound has the advantage of being dynamic: the provider can watch the tendons move in real time to check for subluxation.
Conservative Treatment and Recovery
Most peroneal tendonitis resolves with conservative treatment within three to four weeks. The initial priorities are reducing pain and swelling through rest, ice, and temporarily limiting the activities that provoked the problem. An ankle brace or supportive shoe can help immobilize the area without requiring a full boot, though more severe cases may need a walking boot for a short period.
Physical therapy follows a predictable progression. Early sessions focus on pain management, gentle range-of-motion exercises, and single-leg balance drills on flat surfaces. As pain decreases, you’ll advance to resistance band exercises for ankle strengthening, emphasizing eversion (turning the foot outward) while avoiding extremes of motion. Proprioceptive training, exercises that challenge your balance and ankle stability, starts on level ground and progresses to uneven surfaces once you can perform them with good form and minimal pain. This progression matters because the peroneal tendons are key ankle stabilizers, and retraining that stability is what prevents recurrence.
Returning to sport or full activity too quickly is the most common reason for setbacks. Even once the pain resolves, the tendons need time to rebuild tolerance to load.
Footwear and Orthotics
If your foot structure contributed to the problem, addressing it mechanically can reduce the load on your peroneal tendons going forward. People with high arches and inward-tilted heels benefit from shoes with a firm heel counter and good lateral support. Custom or over-the-counter orthotics with a lateral heel wedge can shift your foot position enough to take strain off the tendons. Research on lateral wedge insoles in people with chronic ankle instability shows that even a small wedge (as thin as 3 millimeters) can improve the reaction time of ankle-stabilizing muscles and enhance balance. Shoes with a wide, stable base and a slightly raised heel tend to be better choices than flat, minimalist footwear during recovery.
When Surgery Becomes Necessary
Surgery is reserved for cases that don’t improve after several months of conservative treatment, or when there’s a significant tendon tear or chronic subluxation. The specific procedure depends on the problem. Tendon debridement removes damaged tissue from a degenerated tendon. Groove-deepening procedures reshape the channel behind the ankle bone so the tendons sit more securely. Retinaculum repair reattaches the band of tissue that holds the tendons in place.
Outcomes are generally favorable. A systematic review of surgical treatment for peroneal tendon dislocation found that over 90% of patients reported good or excellent satisfaction, and the redislocation rate at long-term follow-up was less than 1.5%. Return-to-sport rates ranged from 55% to 100% depending on the procedure, with soft tissue repair and groove-deepening techniques showing the highest rates (83% to 100%). Recovery from surgery takes significantly longer than conservative treatment, typically requiring several months of rehabilitation before returning to full activity.