Ankle injuries are a frequent cause of patient visits to the emergency department and orthopaedic and primary care offices. Although lateral ligament sprains are the most common pathologic conditions, peroneal tendon subluxations occur with a similar inversion mechanism. Multiple grades of subluxation have been described with a recent addition of intrasheath subluxation. Magnetic resonance imaging is the best imaging modality to view the peroneal tendons at the retrofibular groove. Currently, point-of-care ultrasound is gaining clinical ground, especially for the dynamic viewing capability to capture an episodic subluxation. Although conservative treatment may be attempted for an acute injury, it has a low rate of success for the prevention of recurrent subluxation. Surgical procedures of various techniques have resulted in excellent recovery rates and faster return to play. The aim of this paper was to give a complete review of the current literature on peroneal tendon subluxation and to propose a clinical algorithm to help guide diagnosis and treatment. The goal of this study was to heighten clinical awareness to improve earlier detection and treatment of this sometimes elusive diagnosis.
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Often mistaken as simple lateral ankle sprains, peroneal tendon injuries, specifically subluxations, are an underdiagnosed and, therefore, an underreported entity. There are >23 000 injuries of the ankle everyday in the USA.1 It is estimated that peroneal tendon subluxation occurs in 0.3% to 0.5% of traumatic events to the ankle.2 First described as an injury in a ballet dancer in 1803 by Monteggia, peroneal tendon subluxation is commonly associated with sports that require cutting, especially skiing, basketball, ice skating, soccer, rugby and gymnastics.3 Subluxation occurs when the foot is dorsiflexed and inverted with forceful contraction of the peroneal tendons. Conservative management is associated with a low success rate; therefore, the standard of treatment has shifted towards operative for both acute and chronic subluxations.4
Anatomy and function
Comprising the lateral compartment of the distal lower extremity, the peroneal tendons are innervated by the superficial peroneal nerve. The peroneus longus muscle originates at the proximal third of the fibula and lateral condyle of the tibia, whereas the peroneus brevis has its origin in the middle third of the fibula (fig. 1). The muscles course distally and become tendinous approximately 3–4 cm before the ankle joint.5 Within a common tendon sheath, they lie posterior to the lateral malleolus in the retrofibular groove. This groove is primarily concave in shape with an additional fibrocartilaginous ridge that contributes 2–4 mm of depth and provides further stabilisation.6 Cadaver studies have described variations of this retrofibular groove that may predispose the tendons to subluxation. Edwards found that 82% had a concave structure; however, 7% of the fibulae studied were convex; and 11%, flat in shape. He also found that the fibrous ridge was absent in 30% of individuals.7
The fibro-osseous tunnel at the retrofibular groove is contained by four sides (fig. 2). The anterior border is formed by the fibular groove and the fibrous ridge. The posterior wall is created by the deep investing fascia of the leg and the calcaneofibular ligament.4 The calcaneofibular and posterior talofibular ligaments represent the medial frame. The lateral border is created by the superior peroneal retinaculum (SPR), playing a critical role in the stabilisation of the peroneal tendons. Within this groove, the peroneus brevis tendon lies anterior and slightly medial to the peroneus longus tendon. The SPR originates from the periosteum of the lateral malleolus and inserts in the aponeurosis of the Achilles tendon. The SPR provides the primary restraint to the tendons as they sit in the retrofibular groove. After passing this vital junction and heading anteriorly, the tendons track under the inferior peroneal retinaculum that holds the tendons against the lateral calcaneus. By isolating each retinaculum and testing peroneal tendon stability, Purnell et al8 was able to reinforce that the SPR was, in fact, the “key restraining force holding the peroneal tendons in their anatomic positions.”
At the level of the inferior peroneal retinaculum, the tendons are separated by the peroneal tubercle while they course to their individual insertion sites. The peroneus longus tendon turns medially to insert on the plantar aspect of the first cuneiform and base of the first metatarsal. The peroneus brevis tendon courses anteriorly to insert on the base of the fifth metatarsal. The insertion of these tendons dictates their respective muscle function as the primary everters and pronators of the foot. Secondarily, they are also involved in plantar flexion, the longus more so than the brevis. Together, they serve as dynamic stabilisers of the lateral ankle.9
Some anatomic variants exist that may predispose the peroneal tendons to instability and subluxation. The aforementioned variations of the retrofibular groove, including the shape and the depth of the groove itself and the presence or absence of a fibrocartilage ridge may play a key role. Surgical procedures that serve to deepen the groove of the posterior fibula have been used to correct these variations to increase tendon stability.10 In addition, a peroneus quartus muscle or extension of the peroneal brevis muscle belly into the retrofibular groove can cause a crowding-like phenomenon that can stretch the SPR and indirectly aid in subluxation. Finally, a hypertrophied peroneal tubercle found in up to 29% of individuals studied,11 can cause mechanical stress on the peroneal tendons. Case reports have described that these sheering forces contribute to peroneus tendon pathology including subluxation, tenosynovitis and tears.11 12
Mechanism of injury
Acute subluxation occurs in a traumatic injury while the foot is dorsiflexed and inverted with a strong muscular contraction of the peroneal tendons. This force may be great enough to disrupt the primary restraint of the SPR and allow the tendons to displace anteriorly from the retrofibular groove. This type of injury has been described in various sports that involve cutting manoeuvres, such as skiing, soccer, basketball, tennis, gymnastics, football and rugby.3 There has been debate over the years as to whether the actual integrity of the SPR is disrupted or if it is the separation of the SPR from its insertion on the lateral malleolus that is to blame. Basset and Speer were able to demonstrate the significance of a neutral to dorsiflexed ankle in the mechanism of peroneal tendon injury. At a plantar flexion >15°, an inversion injury may strain the SPR and allow subluxation. However, at plantar flexion greater than 25°, the SPR and the peroneal tendons are protected, leaving only the lateral ligaments to be affected.13 The Eckert and Davis14 classification of peroneal tendon subluxation, with modification by Oden, has become widely accepted (fig. 3). Grade 1 subluxation, believed to occur in 51% of injuries, occurs when the SPR is stripped from the lateral malleolus, allowing the tendons to slip anteriorly around the fibrocartilagenous ridge. In a grade 2 injury (33%), the fibrous ridge is elevated with the SPR, increasing the instability of the tendons when reduced. A grade 3 subluxation (13%) occurs when a small fragment of the lateral malleolus is avulsed with the SPR and the fibrous ridge. Although pathognomonic for a peroneal tendon subluxation, the “fleck” sign is seen on fewer than half of the radiographs in patients with surgically confirmed grade 3 subluxations (fig. 4). Oden described a grade 4 subluxation as a complete avulsion or rupture of the SPR from its posterior insertion site, occasionally with the peroneal tendons lying superficial to it.15 16
Most recently, Raikin et al16 described new subtypes of peroneal tendon subluxations in which the SPR remains intact while the anatomic position of the peroneal tendon switches within the retrofibular groove (fig. 5). Type A intrasheath subluxation occurs as the peroneal longus tendon comes to lie deep to the peroneal brevis tendon within the groove. Type B occurs when the peroneal longus tendon subluxates through a longitudinal tear in the peroneal brevis tendon (fig. 6). Both of these situations cause reproducible painful clicking in the retrofibular area. They can be accurately diagnosed by dynamic ultrasound visualisation or occasionally on a static magnetic resonance imaging (MRI) scan as shown in fig. 5. Interestingly, Raikin consistently found a convex shape to the retrofibular groove that may have predisposed the tendons to subluxation as described previously. However, Oliva et al has challenged that these new subtypes are actually grade 1 injuries. Oliva et al9 proposes that the SPR cannot remain intact during such a forceful anatomic shift.
The more common lateral ankle sprain is often a concomitant injury that may lead to stretching of the SPR, subjecting the ankle to chronic instability and recurrent peroneal tendon subluxations. Longitudinal tears of the peroneal tendons, especially the peroneus brevis, can be seen as a result of traumatic subluxation or degenerative tears in the older population. Each tendon has a relatively avascular zone that is more susceptible to tears. The peroneal brevis tendon is vulnerable at the retrofibular groove, as potential shearing forces at the sharp fibrocartilagenous ridge can cause a longitudinal split tear. The peroneal longus tendon is at risk in the cuboid tunnel. These degenerative tears typically do not demonstrate instability within the retrofibular groove.
As in all of medicine, a patient's history is extremely important in making the correct diagnosis. The clinician must keep a high index of suspicion for peroneal tendon injuries, as the described mechanism of injury may be similar to that of a lateral ankle sprain, leading to potential misdiagnosis.4 We offer an algorithm (fig. 7) to guide the clinician in the care of a patient with an acute lateral ankle injury. The patient with an acute subluxation may present with a history of a traumatic dorsiflexion or inversion episode during a cutting manoeuvre. They may report a forceful pop at the posterolateral ankle and will likely have pain at the lateral ankle. The patient may describe a feeling of instability on uneven surfaces, sometimes accompanied by a snapping or popping sensation about the lateral malleolus. With an inversion injury, the clinician should have a higher index of suspicion for peroneal tendon injury if pain is localised to the retrofibular groove, as an isolated posterior talofibular ligament injury is uncommon.
Patients with chronic subluxation may report a history of recurrent ankle sprains or instability. They may have a chronic popping or snapping sensation at the lateral ankle, and they usually describe retromalleolar pain. These symptoms all seem to worsen on uneven surfaces and with rotational motion of the ankle.
On physical examination, acute injuries may present with soft tissue swelling and ecchymosis around the posterolateral ankle. Gross displacement of the peroneal tendons may be seen without reduction. Retrofibular tenderness will be present, and active range of motion testing will produce pain and possibly clicking with plantar flexion and eversion. As with any ankle examination, bony tenderness should be evaluated at the lateral and medial malleoli, the base of the fifth metatarsal and tarsal navicular bones. The patient may have pain at the lateral collateral ligaments as well, and their integrity should be tested with anterior drawer and talar tilt testing. With a dorsiflexion mechanism, it is imperative to evaluate for syndesmotic injury with a squeeze test. Finally, with any severe ankle injury, a Maisonneuve fracture must be ruled out by evaluating the head of the fibula, syndesmosis and the medial malleolus.
Specific testing for the peroneal tendons includes active dorsiflexion and eversion from a plantar-flexed inverted position while the examiner watches and feels for subluxation. Passive circumduction of the ankle may recreate subluxation. In addition, forced dorsiflexion and eversion may cause apprehension. Safran described a provocative test to assess the dynamic stability of the tendons. The patient is to lie prone with 90° flexion at the knee. The ankle is passively plantar and dorsiflexed with resisted eversion while the examiner evaluates for signs of subluxation.17 Keep in mind that absence of subluxation on examination does not rule out this injury.
Patients with varus alignment of the heel, a history of Charcot–Marie–Tooth disease or idiopathic pes cavus should be recognised, as they may be predisposed to chronic lateral instability and peroneal tendon disorders such as subluxation.
As with any ankle injury, clinical judgment, mechanism of injury and examination should guide the need for radiography. In most cases, the clinician may rely on the Ottawa ankle rules. These state that radiographic procedures are indicated if the patient has tenderness to palpation at the distal 6 cm of the fibula and the tibia, to the lateral and medial malleoli, respectively, and the base of the fifth metatarsal or tarsal navicular bone or the inability to bear weight immediately in the emergency department or office for four steps. These clinical guidelines have a reported sensitivity of 94% to 100% and specificity of 15% to 20%, and they have reduced the number of needless radiographs by approximately one third.18 A plain radiograph may be useful in diagnosing a grade 3 subluxation by visualisation of an avulsed piece of the lateral malleolus or fleck sign (fig. 4). The view that best evaluates the peroneal tubercle and the retrofibular groove is the Harris (axial) heel view.
The best modality to assess the integrity of peroneal tendons is MRI. Its soft tissue detail can provide information about the pathologic condition involving the SPR; the tendon sheath and integrity, tenosynovitis; and to a lesser extent, bony abnormalities. A computed tomography (CT) may be helpful in evaluating the osseous anatomy of the retromalleolar area in preparation for a retrofibular groove–deepening procedure.10
However, CT and MRI simply show a static view of the peroneal tendons and their positional relationship within or out of the retrofibular groove. This is not adequate to reveal an episodic subluxation. With the advent of dynamic ultrasound, more research is being conducted on using real-time sonographic imaging to assess the integrity and function of the peroneal tendons at the point of care. This specific modality may be more useful in assessing subluxation than a static MRI earning a positive predictive value of 100%.5 19 20 Ultrasound is also well suited to evaluate the architecture of the tendons for signs of tendinopathy, tears or tenosynovitis. The accuracy and reliability of this imaging modality may be affected by the sonographer's experience. However, in well-trained hands, ultrasonography can be useful in detecting subtle irregularities within a tendon. Rockett et al conducted a prospective study comparing ultrasound with MRI in the detection of peroneal tendon tears. Ultrasonography achieved an accuracy of 94%, with 100% sensitivity and 90% specificity, whereas MRI was 66% accurate, with 23% sensitivity and 100% specificity.21 Ultrasound was the modality of choice for diagnosing the newest described mechanism of intrasheath subluxation. Raikin reports 100% accuracy of the dynamic axial and longitudinal ultrasound to detect the intrasheath subluxation with intact SPR confirmed intraoperatively.16 With many musculoskeletal clinicians moving towards point-of-care diagnosis and therapeutic procedures utilising portable ultrasound machines, we may be better equipped to correctly diagnose peroneal tendon subluxations/dislocations in a timelier manner than previously reported.
Conservative treatment may be considered an option for an acute injury only. Its generally poor success rates, 40% to 57%,22 make it a less-than-desirable option for high-level athletes. Treatment includes immobilisation of the ankle joint in a cast, walking boot or taping. Various methods and positions have been described. The purpose is to immobilise the peroneal tendons in their correct anatomical location until the SPR heals or tightens down. Positioning the ankle in slight plantar flexion and inversion allows the tendons to be neutral for healing.23 Typically, patients are instructed to be non–weight bearing for 2 weeks, followed by 4 weeks in a walking boot. After this, the patient can begin physical therapy with active range of motion and proprioceptive and strength training. Siegel et al described a taping technique involving a lateral malleolar cup that was successful in preventing recurrent subluxation. This was described in the pediatric population for which surgery may be delayed until completion of bone growth.24 Although satisfactory in some cases, most patients eventually require surgery. Escalas et al reported a study of 38 patients with acute peroneal subluxation; after several weeks of conservative therapy, 28 (74%) patients had no improvement and required surgery.25
Surgical correction seems to offer the best results for acute peroneal tendon subluxation and is the only option for recurrent subluxation. It is recommended in younger, higher-level athletes who desire a rapid return to play. Surgical stabilisation may avoid secondary pathologic changes such as tendinopathy or tears that may occur with chronic instability and subluxation. Many operative techniques have been described that have uniformly excellent results. At this point, no prospective randomised studies have been conducted to declare superiority of one study over another.5 22
All procedures have the common goal of stabilisation of the peroneal tendons within the retrofibular groove, whether by correction of anatomic malformation or reinforcement of the primary stabiliser, the SPR.10 Reconstruction of the SPR can be achieved by direct repair with anchors to restore the structural physical restraint to the peroneal tendons in the retrofibular groove. In this procedure, the SPR is isolated and reattached with non-absorbable sutures to drill holes in the lateral malleolus. Using similar procedures, Eckert and Davis described only 3 (5%) of 61 patients who had redislocations, but Adachi et al reported that no redislocations occurred in a series of 20 patients at a 3-year follow-up.14 26 Tenoplasty, using the Achilles tendon or plantaris or peroneus brevis tendon to reconstruct the SPR, has been described by Jones and more recently by Escalas.25 Both authors reported moderate to excellent results.10 27 Most recently, Oliva et al report their level 4 study where 14 of 14 patients treated with retinaculoplasty had no further subluxation and all returned to normal activities.9
Fibular groove deepening for peroneal tendon subluxation has gained popularity for its intuitive concept. The procedure entails isolating the peroneal tendons and SPR and sharply elevating them. A periosteal flap is created in the lateral malleolus, exposing cancellous bone. This bone is then curetted to a depth of 6–8 mm (normal depth, 2–5 mm). The periosteal flap is then tamped down, and the peroneal tendons are allowed to lie in a deeper groove. Although a technically difficult procedure, most case studies have had excellent results and high patient satisfaction ratings. Zoellner and Clancy reported nine of nine patients without recurrence.28 Using a similar groove-deepening procedure in combination with an SPR reattachment, multiple authors have reported excellent results with most of the patients able to return to their preinjury level of play.10 29 30 Using the fibular groove-deepening technique for the latest described intrasheath subluxation, Raikin has reported successful correction of 13 of 14 patients. The isolated unsuccessful case was a type B subluxation, where after correction of the longitudinal tear in the peroneal brevis, the tendons were found to have become a type A with true juxtaposition of the longus tendon to the brevis.16
First described by Kelly in 1920,31 the idea behind a bone block or lateral malleolar osteotomy is to deepen the retrofibular groove while using a bone graft as a physical restraint to the peroneal tendons. This procedure and variations of it have shown fair to excellent results for non-recurrence of dislocation; however, patients reported multiple complications including crepitus near the ankle, tendon dislocation and displacement of bone graft, pain and loose bodies requiring a second surgical procedure.22
Finally, rerouting of the peroneal tendons beneath other structures, primarily the calcaneofibular ligament, has been described with good to excellent results. This can be done by dividing the calcaneofibular ligament and transposing the peroneal tendons behind it as a primary restraint. Alternatively, the peroneal tendons can be separated and reattached after taking a new course under the calcaneofibular ligament. The inherent risk of this procedure is weakening of the divided structure; however, Steinbock and Sarmiento and Wolf reported good to excellent results, without recurrence of dislocation or instability.32 33 34
Postoperatively, patients are generally placed in non–weight-bearing casts for approximately 2 weeks, followed by a walking boot for an additional 4 weeks. At this point, patients enter rehabilitation under the guidance of a skilled physical therapist for range of motion, proprioceptive and strength training. Recommended initial aerobic activities include swimming and cycling. After demonstrating appropriate progression of strength and functionality, patients can progress to more sport-specific training. Commonly, patients are able to return to play at their previous level in 3–4 months.
Peroneal tendon subluxation is estimated to occur in 0.3% to 0.5% of traumatic events to the ankle.2 Therefore, clinicians must keep a high index of suspicion for this injury in patients that present with a dorsiflexion or inversion mechanism. History and physical examination can give clues to subluxation, including retrofibular pain, a snapping sensation near the lateral ankle or chronic ankle instability that worsens on uneven surfaces. Proper imaging includes plain radiography and MRI to evaluate the peroneal tendons and the SPR. Recent advances in point-of-care ultrasonography have proven extremely useful in evaluating the dynamic function of the tendons and can visualise episodic subluxations. Conservative treatment can be considered in acute subluxations in non-competitive athletes; however, it is notorious for low success rates. Given its uniform excellent success rates, surgical intervention has become the standard of care for acute subluxations in high-level athletes and should be the only option for chronic subluxation. At this time, there is not enough evidence to advocate for a certain type of corrective procedure. A new form of intrasheath subluxation has recently been described that is well defined with dynamic ultrasound and may be successfully treated by a retrofibular groove-deepening surgical procedure.16 Rehabilitation including range of motion, proprioceptive and strength training can accomplish return to play in approximately 12–16 weeks.
What is already known on this topic
▶ Peroneal tendon subluxation is often misdiagnosed as a lateral ankle sprain. Imaging includes radiography, MRI and dynamic musculoskeletal ultrasound. Conservative treatment may be considered for acute injuries in the non-athlete; however, low success rates point towards surgical correction for improved outcomes and expedited return to play.
What this study adds
▶ This paper provides a comprehensive review of the current literature on peroneal tendon subluxation and proposes a clinical algorithm to guide diagnosis and treatment.
The authors thank Alice McKinney, Medical Illustration Unit, Mayo Clinic; Jeffrey J Peterson, MD, Department of Radiology, Mayo Clinic; and Diane Morell and Katherine Purcell, Academic Research Support, Mayo Clinic, for their assistance in preparing this manuscript.
Competing interest None.
Provenance and peer review Not commissioned; externally peer reviewed.
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