Peroneal dysfunction: an under diagnosed cause of lateral ankle pain

Lateral ankle sprain is a common sports injury. Alicia Filley explains why peroneal dysfunction may be to blame for the persistent pain and instability after the acute injury has healed. 

 2019 Golden State Warriors forward Kevin Durant (35) goes down with an injury holding his right ankle. Credit: Kelley L Cox-USA TODAY Sports

Ankle sprains generate a significant amount of emergency room charges in the United States with a significantly greater number of lateral than medial sprains noted(1). A systemic review by researchers in Dublin found that ankle sprains occurred more commonly in females than in males, and in adolescents than adults(2). As many as 30% of all sports injuries occur at the ankle, and sports played on indoor courts had the highest incidence of ankle sprains(2,3). Chronic ankle instability (CAI) persists in about 20% of people diagnosed with ankle sprains, and many continue to experience pain in the lateral ankle long after the sprain has healed(3).

One possible source for the continued instability and discomfort is undiagnosed damage to the peroneal tendons. Damage to the peroneal tendon may go undiagnosed in 40% or more of sprains, despite the fact that they serve as an integral part of the stability of the lateral ankle(4).


The peroneus longus and brevis comprise the lateral compartment of the lower leg. The longus originates from the proximal fibula, with attachments on the intermuscular septum and lateral tibia. The brevis arises further down the distal fibula, also attaching to the intermuscular septum and lies beneath the longus. The two muscle tendons join together in one tendon sheath to pass through the retro-malleolar groove over the posterior talofibular ligament and under the superior peroneal retinaculum (see figure 1). The superior peroneal retinaculum is primarily responsible for maintaining the tendons within the groove and preventing dislocation.

Once past the retromalleolar groove, the tendons separate into individual synovial sheaths. At the peroneal tubercle, the sheaths thicken, forming the inferior peritoneal retinaculum. The brevis tendon courses above the peroneal tubercle and attaches to the base of the fifth metatarsal; the longus, however, goes under the tubercle and into the cuboid tunnel, travels obliquely under the foot, and inserts at the plantar surface of the medial cuneiform bone and the base of the first metatarsal.

Figure 1: Anatomy of the lateral ankle

The peroneus tertius lies within the anterior compartment of the lower leg, completely separate from the longus and brevis. This smaller muscle is present in 90% of the population and functions in unison with the foot extensor muscles(5). Up to one-fourth of individuals also have an unusual variant muscle called the peroneus quartus(5). It arises from the peroneus brevis, shares the common tendon sheath, and attaches to the peroneal tubercle.


The peroneal tendons cross the ankle joint together in their shared tendon sheath and then divide, cross several different joints in the foot, and attach on either side of the foot. Thus, the function of the brevis and longus in the foot can differ, while they work together at the ankle. Specifically, the longus pronates the first metatarsal and everts the foot, accounting for 63% of the eversion force(4). Most active during mid and late stance, the muscles together assist in plantar flexion, pronation, and ankle stabilization.

The peroneals are considered primary stabilizers of the lateral ankle because a sudden ankle inversion triggers a contraction in these muscles first(4). Peroneal muscle dysfunction may contribute to CIA since if the activation of the peroneals is delayed, the integrity of the lateral ankle complex can be repeatedly compromised by frequent inversion. However, in what may be a ‘chicken or egg’ situation, a study conducted in Vienna evaluated 58 runners who suffered acute ankle sprains after complaints of lateral ankle pain up to four weeks prior. The researchers found that 95% of the subjects had preexisting peroneal tendinosis preceding the acute injury(6).


Peroneal muscle disorders fall into three categories: tendinopathy, subluxation and dislocation, and splits and tears. Peroneal injuries are usually the result of repeated inversion strain. Athletes with peroneal pathology usually exhibit a pes cavus foot or cavovarus hindfoot. They typically play multi-directional field and court sports.

Athletes with peroneal tendinosis usually complain of posterolateral ankle pain over the retromalleolar groove that gets better with rest but flares again with activity. The pain may extend up along the lateral leg. There may be a palpable mass or thickening within the tendon along with swelling behind the fibula or along the lateral calcaneus. Pain is elicited with resisted eversion, plantar flexion of the first ray, and inversion stretch. Magnetic resonance imaging (MRI) and ultrasound (US) are the most sensitive for diagnosing tendinopathy. There may be concurrent splits or tears in the tendons. An X-ray will rule out a fifth metatarsal stress fracture.

Subluxation and dislocation are usually associated with a forceful inversion injury. Active ankle rotation or resisted dorsiflexion and eversion may reproduce subluxation. These types of injuries can be graded according to the degree of disruption in the SPR. When the SPR is avulsed from the lateral malleolus, the tendons may slide out of the retromalleolar groove, resulting in a Grade I injury. In a Grade II injury, the fibrocartilagenous ridge that extends from the fibula and helps form the retromalleolar groove also avulses. A Grade III injury occurs when a small fragment of bone is also torn from the fibula. When the SPR avulses from the calcaneus, the fibrous band is torn and the tendon may lie outside of the SPR altogether. This is a Grade IV injury.

When the SPR is compromised during an inversion injury, the brevis can sublux from its deep position and lie superficial to the longus tendon. This can result in a tear in the brevis tendon. Inversion injuries can also cause excessive pressure on the brevis tendon as the longus presses against the fibula. Caught in the middle, the brevis tendon may give-way and split. If the tendons are degenerate due to repeated injury or long-standing tendinosis, they may rupture completely.

Painful Os Peroneum Syndrome

A sesamoid bone, not often visible on X-ray, lies within the peroneus longus tendon as it enters the cuboid tunnel. Like other bones, it can be bruised and broken. Repeated trauma may result in callus formation and contribute to longus tendinopathy and tendon tears. Symptoms arising from this area are termed painful os peroneum syndrome (POPS). Trauma to the longus may also occur in this are due to a hypertrophied peroneal tubercle. The tendon, along with the sural nerve, gets compressed between the tubercle and the os peroneum, causing a tear or split in the tendon and symptoms of tingling or numbness in the foot(7).


Peroneal tendinosis usually responds well to conservative treatment. Like other tendinopathies, a period of brief initial rest and non-steroidal anti-inflammatory medication followed by load modification calms the symptoms. If not, clinicians recommend immobilization in a walking boot for up to six weeks(4). Manage the load increase on the muscle closely, beginning with gentle range of motion without resistance. Progress strengthening activities as tolerated, staying within an acceptable pain level of two to three out of 10 for 24 to 48 hours after load progression (see figure 2).

Figure 2: Strengthening exercises for peroneal rehabilitation

Isometric holds: with resistance band around the foot and stabilized under the opposite foot, hold the ankle in neutral dorsiflexion as the leg abducts from the hip. The resistance will trigger a contraction in the peroneals. Hold for 10 seconds and then return to start position. Perform 10 reps and progress to 15 reps. Once able to tolerate the isometric load, progress to actively everting the foot against resistance while keeping the ankle neutral. 

Active eversion/inversion: Once able to tolerate foot eversion with a neutral ankle, perform full ankle eversion and inversion with plantar flexion and dorsiflexion. Progress reps and resistance as tolerated. 

Step eversion hold: Begin with first two metatarsals and inside of heel on a slightly elevated surface. Hold the ankle in neutral for 10 seconds with the rest of the foot unsupported. Progress to 15 reps. 

Active inversion to eversion: In same position as eversion hold exercise, begin with ankle in inversion. Actively contract the peroneals to elevate the lateral side of the foot and evert the ankle. Begin exercises slowly and with control and progress to quick response movements to retrain the peroneals to contract on inversion. 

As most individuals with peroneal problems demonstrate a pes cavus foot, evaluate orthotic needs. Often orthotics with lateral posting, lateral arch fill, and flaring help prevent excessive supination. Consider slight posting under the first metatarsal to assist the longus with plantar flexion at push off. Gait patterns may need to be modified as well. Running with a forefoot strike may aggravate the tendons, therefore, encourage a midfoot strike to relive some of the stress.

Subluxation or dislocation after an acute injury should be treated with a period of immobilization. A removable cast boot used from one to four weeks protects the tendons from any additional stretch while they heal(5). Once stable, begin gentle active range of motion. Typically if torn, the retinaculum will not heal without surgical repair. However, repair isn’t always necessary. Strengthening activities and balance training combined with appropriate bracing may allow the athlete to return to play without pain and with adequate stability (see figure 3). Sport specific training including cutting, jumping, and running can usually begin six weeks after injury.

Figure 3: Balance activities for peroneal retraining

The star excursion balance test (SEBT): The SEBT is useful for diagnostic purposes as well as retraining. Standing on the center point, the subject reaches with the opposite leg to touch their toe to the line. The focus is on unilateral stance control with movement. 

Progress proprioceptive training, shown here for ACL rehab, as tolerated from both feet on an unstable surface to functional movement on an unstable surface, to unilateral stance on an unstable surface. Eliciting quick responses from the peroneals is key to neuromuscular retraining and return to sport stability.  Ankle bracing may be necessary to execute advance training and return to sport. 

Peroneal tears, splits, and ruptures most often need surgical repair in order for the athlete to return to sport with proper stability and function. Surgical repairs are usually successful, with up to 80% of those with splits or tears returning to sport in 12 weeks. Ruptures require a more extensive procedure with tendon transfer or grafting that will prolong return to sport.

Practical implications

  • Peroneal tendon pathology may precede acute lateral ankle sprain. Therefore, treat all complaints of otherwise undiagnosed lateral ankle pain as suspected tendinosis in the peroneal muscles in an attempt to prevent further ankle trauma.
  • Pes cavus feet may be more susceptible to peroneal pathology and thus lateral ankle sprain. Consider orthotic intervention and changing running gait patterns in those with complaints of lateral ankle pain.
  • Treat acute ankle sprains with a period of immobilization to protect the tendons. Once returning to loading, begin with active range of motion and progress load cautiously.
  • Extensive neuromuscular training with balance activities promotes prompt activation of peroneals during ankle inversion.
  • Surgery isn’t always necessary to treat subluxation and dislocation. However, continued bracing during sporting activities may be needed to protect the ankle.


  1. Sports Health.2016 Nov; 8(6): 547–552
  2. Sports Med.2014 Jan;44(1):123-40
  3. Avicenna J Med. 2016 Oct-Dec; 6(4): 103–108
  4. EFFORT Open Rev. 2017;2:281-92
  5. Podiatry Management. 2017 Sept;145-152
  6. Knee Surg Sports Traumatol Arthrosc.2016 Apr;24(4):1175-9
  7. J Korean Foot Ankle Soc. 2018;22(3):131-134



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