Peroneal Tendonitis: Causes, Diagnosis, Treatment, and What It Means for Athletes

Key Takeaways

“Peroneal tendonitis” is the everyday name, but an international expert consensus now prefers peroneal (fibularis) tendinopathy for persistent peroneal tendon pain and loss of function related to mechanical loading.
Peroneal tendon problems range from tendinopathy to longitudinal tears, complete ruptures and tendon instability (subluxation or dislocation), and more than one of these can be present at the same time.
Peroneal tendonitis is closely tied to ankle sprains: in one surgical series of 61 patients with chronic lateral ankle instability, 77% had peroneal tenosynovitis.
Both ultrasound and MRI are appropriate imaging tools, but imaging is not always needed, and peroneal tendon findings on MRI can also be seen in people without peroneal symptoms.
Conservative, load-based management is the starting point recommended by an international expert consensus, although the underlying evidence is mainly level IV and V; surgery is mainly considered for symptomatic tears that do not settle, symptomatic complete ruptures in active patients and tendon dislocation, particularly in athletes.
In my clinical experience, patients often fall into two groups: those whose symptoms start with a delay after an ankle sprain, and those whose pain follows overuse or an unusual load, such as a weekend hike.
In my clinical experience, NSAIDs can ease the symptoms but do not usually resolve the problem on their own, and I prefer to combine them with physiotherapy-led exercise.
In my experience, athletes often push through the pain until the end of the season, which can make the problem worse. Rest alone does not necessarily solve it, and physiotherapy with tendon-loading exercises can be started early.
When the work itself causes the pain, I find that reviewing ergonomics and work tasks with an occupational health physiotherapist can be particularly valuable.

Introduction: Why Peroneal Tendonitis Deserves More Attention

An international consensus panel describes peroneal tendon injuries as a significant cause of lateral ankle symptoms in the active population and stresses that chronic peroneal tendinopathy carries a risk of long-term problems if it is not recognised and treated early.[1] A narrative review describes peroneal tendon pathology as an under-appreciated source of lateral hindfoot pain and dysfunction that can be difficult to distinguish from lateral ankle ligament injuries.[2]

This article covers what peroneal tendonitis is, why it develops, how it is diagnosed, which treatments have evidence behind them, and what all of this means for athletes who want to return to sport.

What Is Peroneal Tendonitis? (And Why Experts Now Say “Tendinopathy”)

The two peroneal (fibularis) muscles, peroneus longus and peroneus brevis, together form the lateral compartment of the lower leg. Near the ankle, their tendons curve around the tip of the fibula inside a fibro-osseous channel called the superior peroneal tunnel.[1] The peroneus longus muscle turns fully tendinous about 3–4 cm above the distal fibula, whereas the peroneus brevis muscle extends lower into the groove behind the bone.[1]

Historically, “tendinitis” was the first term used for tendon pain, thickening and impaired function. The ICON 2019 expert consensus, however, concluded that peroneal (fibularis) tendinopathy is the preferred term for persistent peroneal tendon pain and loss of function related to mechanical loading. The panel noted that “tendinopathy” does not assume a specific pathological or biochemical process, which cannot routinely be assessed in the clinic.[3] The same consensus defines a tendon tear as a macroscopic (visible without magnification) discontinuity of a load-bearing tendon, a distinct clinical entity that may need different management.[3]

In this article, “peroneal tendonitis” is used because it is the term most people search for, but the evidence discussed refers to peroneal tendinopathy and related disorders.

The spectrum of peroneal tendon disorders

The ESSKA-AFAS consensus recommends classifying peroneal tendon pathology into three categories: tendinopathy, tear/rupture, and instability/dislocation.[1] A tear usually refers to a longitudinal or incomplete lesion, whereas a rupture means complete separation of the tendon ends.[1] The narrative review also notes that these pathologies are frequently encountered in patients with chronic lateral ankle instability or a cavovarus foot, and usually result from prolonged, repetitive athletic activity or ankle inversion injuries.[2]

Peroneal Tendonitis Symptoms: What It Feels Like

Patients typically present with posterolateral ankle pain, behind and to the outer side of the lateral malleolus (the outer ankle bone), that worsens with activity and improves with rest. Swelling behind the fibula or along the outer wall of the heel bone, tenderness along the course of the tendons and pain with resisted eversion are common findings, and the examination may also check for crepitus and “popping” at the back edge of the distal fibula.[2]

The location of pain can give clues:

Peroneus brevis tears usually cause pain around the distal fibula.[1]
Peroneus longus tears more often cause pain near the peroneal tubercle and the cuboid tunnel on the outer side of the foot.[1]
Examination may reveal weakness when turning the foot outward (eversion) or pushing the first ray down (first-ray plantarflexion).[1]
In tendon dislocation, there is typically swelling and tenderness behind the outer ankle bone, and the dislocation can often be reproduced by resisted eversion.[1]

In my clinical experience, peroneal tendonitis is a fairly common cause of lateral ankle pain. Patients usually describe pain on the outer side of the ankle that tends to get worse with load, but it can initially be surprisingly hard to localise. Some feel it near the tendon insertion in the foot, others behind the lateral malleolus, and some even report pain extending up into the calf. In some patients there is swelling and occasionally redness over the area. The pain may settle overnight and then return after the first steps the next morning. When the tendon sheath is also inflamed (tenosynovitis), crepitus can sometimes be felt over the sheath.

What Causes Peroneal Tendonitis?

In practice, I find that patients with peroneal tendonitis can roughly be divided into two groups. The first group has injured the ankle, typically through a sprain that initially involves some degree of ligament injury. The tendon symptoms then start with a delay: the original sprain may have healed reasonably well, but after this first phase of recovery the pain increases again and starts to flare with activity. The second group develops pain from load rather than from an injury. Some do a lot of physical work or work on their feet, while others have simply had an unusual period of load. A typical example in my practice is an office worker whose pain clearly began after a weekend of hiking in Lapland.

Ankle sprains and chronic ankle instability

Lateral ankle sprains and chronic ankle instability are important associated conditions. In a surgical series of 61 patients undergoing lateral ligament reconstruction for chronic ankle instability, none had an isolated ligament injury. Peroneal tenosynovitis was found in 47 of 61 patients (77%), an attenuated peroneal retinaculum in 33 of 61 (54%), and a peroneus brevis tear in 15 of 61 (25%).[4]

A retrospective review of 40 patients who underwent peroneal tendon repair found peroneus brevis tears in 88%, combined brevis and longus tears in 37%, a low-lying peroneus brevis muscle belly in 33%, lateral ankle ligament disruption in 33%, and peroneal subluxation in 20% at surgery.[5] The authors concluded that lateral ligament incompetence, combined tears and a low-lying muscle belly commonly coexist in patients with peroneal tendon injuries.[5]

Anatomy and “overstuffing” of the tunnel

The ESSKA-AFAS panel agreed that several anatomical variations may predispose to peroneal tendon pathology, and that “overstuffing” of the peroneal tunnel is an important factor. In the panel’s view, the volume of the tunnel matters more than the exact shape of the groove.[1] A low-lying muscle belly in itself does not necessarily predispose to pathology, but the crowding it can cause in the tunnel likely does.[1] The panel also discussed accessory muscles such as the peroneus quartus, which have been linked to pain and swelling around the lateral malleolus, although an association with tendon tears remains controversial. No clinical evidence is available on the relation between the peroneal tubercle and peroneal tendon pathology, but the panel agreed that a prominent tubercle may predispose the tendons to recurrent tears. The os peroneum, a small accessory bone inside the peroneus longus tendon, has an estimated incidence of 4–30%, and its calcification may potentially predispose the tendon to tears.[1]

Foot shape: the cavovarus foot

The consensus also states that chronic loading of the tendons, as seen in a cavovarus (high-arched, heel-turned-in) foot, may predispose them to pathology.[1] In a case review of 22 patients with primary peroneus longus tendinopathy, 82% had a cavo-varus hindfoot position, and the tendon injury was located at the cuboid notch in 17 of 22 cases.[6]

What Peroneal Tendonitis Means for Athletes

Who is at risk?

Tendon dislocation is described in background data summarised by a systematic review as occurring in 0.3–0.5% of all traumatic ankle events and as often misdiagnosed and therefore underreported. The same review notes that it is most prevalent in athletes, particularly in sports requiring cutting movements such as skiing, soccer, basketball, ice skating and gymnastics.[7] Dislocation typically occurs when the peroneal muscles contract suddenly and eccentrically during acute dorsiflexion of the foot, with or without inversion.[7]

The link between ankle sprains, weakness and recurring injury

For athletes, peroneal problems rarely exist in isolation. A meta-analysis found that ankles with functional ankle instability had weaker concentric eversion strength than stable ankles, although the standardised mean difference was small (0.224).[8] A later systematic review and meta-analysis of systematic reviews reported strong evidence for deficits in dynamic balance, peroneal reaction time and eversion strength in non-specific ankle instability, while cautioning that these findings may not translate directly to the chronic ankle instability population.[9]

A review of peroneal tendon disorders recommends that the clinical examination include an assessment of foot type, palpation of the peroneal tendons behind the fibula during resisted dorsiflexion and eversion, and testing of the lateral ankle ligaments.[2] In practical terms, an athlete with repeated sprains and persistent lateral ankle pain may benefit from assessment of both ligament instability and peroneal tendon pathology, so that one is not treated while the other is missed.

From time to time, I also see peroneal tendonitis in athletes. In my experience, they often come from sports that involve repeated forceful push-offs, such as combat sports, basketball or orienteering, where lateral stability of the ankle combined with eccentric forces is particularly important. These situations can sometimes be challenging, because athletes are often reluctant to take a break from their sport, and their training is frequently quite one-sided. Avoiding forceful push-offs may hardly be possible in their sport, so stepping away from training can be very difficult for them. In my experience, many athletes may also make the problem worse by pushing through the pain, often until the end of the training season. Sometimes the pain has already been getting progressively worse for several months, but the athlete has had a competitive season they wanted to finish, or a main competition they have been training for, and has planned to deal with the problem only after the season.

What I often explain to them is that rehabilitative exercises and physiotherapy are still an important part of recovery. Reducing load is of course important in the acute phase, but for athletes the role of active rehabilitation is especially emphasised. Rest alone does not necessarily resolve the problem, and it can be helpful to include physiotherapy and tendon-loading exercises from the early stages onwards.

Athlete status changes the treatment decision

The ESSKA-AFAS panel considered the distinction between athletes and non-athletes an important factor for both treatment and outcomes.[1] This matters most for tendon dislocation and for decisions about correcting foot alignment, both of which are discussed below.

How Peroneal Tendonitis Is Diagnosed

For an acute ankle injury, the consensus recommends that initial assessment follow the Ottawa ankle rules. Specialist review is warranted when imaging shows a “fleck sign” or distal fibular fracture, when there is a clear history of a popping sensation or frank tendon dislocation, or when the person cannot bear weight one to two weeks after the injury.[1]

Ultrasound vs MRI

The panel concluded that both ultrasound and MRI are appropriate for evaluating the peroneal tendons, with the choice depending on clinician preference, user expertise and availability.[1] In a small, surgically selected cohort, a 2024 study of 21 consecutive patients who had both MRI and ultrasound before peroneal surgery compared the imaging with intraoperative findings:[10]

Tendon tears: ultrasound sensitivity 88% and specificity 100%, versus 100% and 100% for MRI.
Tendinopathy (18 patients): both ultrasound and MRI had 100% sensitivity and specificity.
Subluxation (only 3 patients): ultrasound was 100% sensitive versus 66% for MRI, with both 100% specific.

The authors attributed ultrasound’s advantage for subluxation to its dynamic nature: the examiner can have the patient actively move the ankle and watch the tendons slip, whereas MRI captures a static image.[10] Because only surgical patients were included, the study cannot tell us how well either test performs in the broader population of people with lateral ankle pain.[10]

If imaging is negative but clinical suspicion remains high, the consensus reserves peroneal tendoscopy (a minimally invasive camera examination of the tendon sheath) for that specific situation.[1]

Imaging findings are not the same as a diagnosis

The ICON consensus notes that imaging is not always necessary for a diagnosis of tendinopathy.[3] This is important because peroneal “abnormalities” on scans are common. In a retrospective review of 294 foot and ankle MRIs that excluded patients with documented inversion injuries, ankle sprains or lateral ankle trauma, 103 (35%) showed some form of peroneal tendon pathology, leading the authors to conclude that a sizeable share of asymptomatic individuals could have peroneal findings on MRI.[11] Similarly, anatomical variants thought to predispose to peroneal disorders were seen on MRI in volunteers with asymptomatic ankles; a peroneal tubercle, for example, was identified in 36 (55%) of the ankles studied.[12]

In practice, the symptom picture is often fairly straightforward, and the diagnosis can often be made on clinical examination alone. In more complicated situations, imaging may be helpful. In my experience, MRI often gives the clearest picture in these situations, although ultrasound is also an appropriate method and the changes can sometimes be seen on ultrasound as well. When the situation is unclear, a plain X-ray is usually also taken as one of the basic investigations.

Peroneal Tendonitis Treatment: What the Evidence Supports

Conservative management comes first

The ESSKA-AFAS consensus states that conservative management should be considered in all patients with peroneal tendon pathology.[1] Its recommendations include:[1]

In the acute phase, treating any additional injury (such as a lateral ligament rupture) with ice, compression and elevation.
Starting weight bearing once it is painless, followed by range-of-motion and tendon-loading exercises.
Avoiding routine immobilisation in uncomplicated peroneal tendinopathy. Acute tendon dislocation and some surgical repairs are managed with immobilisation, as described below.
Considering shockwave therapy when symptoms persist beyond three months; this rests on some suggestion of benefit in lower-extremity tendinopathy generally rather than on peroneal-specific data.
Not using platelet-rich plasma (PRP), because there is insufficient evidence to support its use in peroneal tendinopathy.

The panel was open about the limits of this evidence: outcomes of conservative treatment for acute peroneal tendinopathy are supported only by limited and varied data, and the overall recommendations rest mainly on level IV and V evidence.[1]

In my practice, the first-line treatment we recommend for many patients is rest. If the symptoms persist, I refer the patient to physiotherapy. Unless the situation is clearly acute and likely to settle with a short period of rest, I tend to refer patients to rehabilitative physiotherapy quite early. Anti-inflammatory painkillers (NSAIDs) can provide symptom relief for many patients, and they are often prescribed at the start. In my view, however, they do not usually resolve the problem itself, so I prefer to combine them with physiotherapy-led exercise. In complicated cases, I usually refer the patient to an orthopaedic surgeon for assessment.

On corticosteroid injections, the panel reached no consensus in its discussion of os peroneum-related problems. It advised that any benefit be weighed against the risk of tendon rupture, while acknowledging that the reported rupture risk after ultrasound-guided injection into the peroneal tendon sheath is low.[1] A narrative review adds that, in refractory tendinosis, immobilisation in a short-leg cast or walker boot for six weeks may be helpful, and that the authors do not use corticosteroid injections in their institution because of the risk of iatrogenic rupture.[2]

Patients often ask me whether a cortisone injection could help. My answer is often that it is not worth it, because in my view the tendon does not necessarily respond very well to cortisone. Many patients are also worried about their own tendons and do not want to risk weakening them.

Work, sick leave and everyday load

In my clinical experience, walking is often painful for these patients, and those with physically demanding jobs in particular may need sick leave. Office workers, in turn, may find that the commute itself aggravates the pain, and for them I often suggest remote work when it is possible. In my practice, however, if the pain does not flare at work itself but only on the way there, the commute alone is generally not an indication for sick leave; the aim is rather to arrange transport to the workplace in a way that spares the ankle.

Fortunately, in my experience, for many patients the cause is simply an unusual load, such as a weekend hike that does not happen very often. Changing the load profile and avoiding that particular load is then usually not a major problem. The situation is more difficult when the pain is purely work-related and the work itself exposes the patient to it. In these cases, I find it particularly valuable to review with an occupational health physiotherapist whether anything can be done ergonomically, and whether the job description can be modified physically so that the work can be done in a less straining way.

When is surgery considered?

Surgery is mainly reserved for specific situations:

Tears: treatment should be limited to symptomatic patients and should start conservatively. The panel noted cadaveric studies finding peroneal tears in 11–38% of ankles, and assumed that only a proportion of all tears become symptomatic.[1]
Complete rupture of one tendon: this can be treated conservatively in an inactive, asymptomatic person, whereas symptomatic ruptures in active patients usually require repair.[1]
Acute dislocation: non-athletes may be offered conservative treatment but should be warned of a 50% chance of recurrent dislocation; surgery is recommended for elite athletes with either acute or chronic dislocation.[1]

Return to Sport After Peroneal Tendon Injury

After peroneal tendonitis or a related tendon injury, return-to-sport outcomes depend heavily on the type of injury.

After surgery for dislocation, outcomes are generally favourable. A systematic review of 14 studies found a redislocation rate below 1.5% at long-term follow-up. Return-to-sport rates were 83–100% after retinaculum repair and 91–100% after groove deepening combined with retinaculum repair, with the combined procedure showing a significantly higher return rate (p = 0.022). Mean time to return was 3.0 months after retinaculum repair alone and 4.6 months after the combined procedure, a difference that was not statistically significant.[7] All included studies were rated low quality, so these figures should be interpreted with caution.[7]

After surgery for tears, the picture is more mixed:

In 30 patients treated operatively for peroneal tears, only 46% successfully returned to sports at an average follow-up of 31 months, and many had residual scar tenderness (58%) or lateral ankle swelling (54%).[13]
In contrast, a long-term study of debridement and primary repair found that 17 of the 18 patients who responded to follow-up (out of 34 treated) returned to full sporting activity without limitation, at an average follow-up of 6.5 years.[14]
In the 40-patient review mentioned above, 98% returned to full activities without pain at final follow-up, while major complications (continued symptoms or revision surgery) occurred in 10%.[5]

None of these studies were controlled trials, and differences in patient selection, injury severity and outcome definitions may contribute to the variation.

For elite athletes, the consensus adds two important cautions. First, elite athletes may not return to their pre-operative level after surgery for peroneal tendon rupture. Second, correcting hindfoot malalignment in athletes is probably best avoided, because in the panel’s experience asymptomatic idiopathic hindfoot varus is not uncommon in athletes and correcting it may harm elite performance.[1]

In the context of post-operative rehabilitation, the panel also recommended that return to running should not be based on time alone, but on the person’s ability to perform a single heel rise, overall strength, neuromuscular control and proprioception.[1] It acknowledged that post-operative rehabilitation protocols currently lack sufficient scientific support for a fully evidence-based protocol.[1]

Practical Recommendations for Athletes and Coaches

The following points summarise how the evidence above can be applied to peroneal tendonitis in practice. They represent clinical synthesis of the cited sources rather than a validated treatment protocol.

Do not assume every lateral ankle pain is “just a sprain.” Persistent pain behind or below the outer ankle bone, especially if it worsens with activity or comes with clicking, may warrant assessment for peroneal tendon involvement.
Check for associated instability. Peroneal tendon problems frequently coexist with lateral ligament injury, so both may warrant evaluation.
Treat imaging as a tool, not the diagnosis. Findings on MRI or ultrasound are best interpreted alongside the clinical picture.
Start with progressive loading, not rest alone. Current consensus favours tendon-loading exercise and avoiding routine immobilisation in uncomplicated tendinopathy; tendon dislocation, refractory cases and post-operative care are different.
Seek early specialist assessment for suspected dislocation. A popping sensation followed by tendons snapping over the outer ankle bone is different from tendinopathy, and athletes may benefit from early surgical opinion.
Base return to running on function. After surgery, current consensus favours the ability to perform a single heel rise, strength and neuromuscular control over the number of weeks since injury.

Conclusion: What to Remember About Peroneal Tendonitis

Peroneal tendonitis, more accurately called peroneal tendinopathy, sits within a wider spectrum of disorders that includes tears, ruptures and tendon instability. It is closely linked to ankle sprains and chronic instability, as illustrated by the 77% rate of peroneal tenosynovitis in one surgical series of patients with chronic lateral ankle instability.[4]

Diagnosis rests on a careful history and examination, with ultrasound or MRI used when needed and interpreted in context. Treatment usually begins conservatively, with progressive loading and, in uncomplicated tendinopathy, avoidance of immobilisation, while surgery is mainly considered for symptomatic tears that do not settle, symptomatic ruptures in active patients and tendon dislocation, particularly in athletes. Because much of the evidence base consists of small case series and expert consensus, decisions are best individualised.

In my clinical experience, the diagnosis can often be made on clinical examination, and many cases settle once an unusual load has been identified and avoided. The more difficult cases are those in which the work itself or a one-sided sport keeps loading the tendon, and athletes in particular may continue training through months of worsening pain. For these patients, NSAIDs may ease the symptoms, but in my view physiotherapy and tendon-loading exercises from the early stages onwards are an important part of treatment.