Syndesmotic ankle injury (high ankle sprain)

INTRODUCTION — A syndesmotic ankle sprain is an injury to one or more of the ligaments comprising the distal tibiofibular syndesmosis; it is often referred to as a "high ankle sprain." Compared with the more common lateral ankle sprain, the high ankle sprain causes pain more proximally, just above the ankle joint, and is associated more often with significant morbidity. Diagnosis can be difficult and clinicians should consider the possibility of syndesmotic injury in athletes with pain or injury around the ankle or lower leg. Treatment too is different from typical ankle sprains and surgery may be necessary, making recognition important for optimal recovery.

The risk factors, clinical presentation, diagnosis, and management of high ankle sprains in the absence of any associated fracture is reviewed here. The common ankle sprain and other ankle-related injuries are discussed separately. (See "Ankle sprain in adults: Evaluation and diagnosis" and "Foot and ankle pain in the active child or skeletally immature adolescent: Evaluation" and "Ankle fractures in adults" and "Overview of foot anatomy and biomechanics and assessment of foot pain in adults" and "Achilles tendinopathy and tendon rupture" and "Non-Achilles ankle tendinopathy" and "Talus fractures".)

EPIDEMIOLOGY AND RISK FACTORS — High ankle sprains are much less common than the typical lateral ankle sprain. Using clinical diagnostic criteria (ie, not radiologic), the largest observational studies report that high ankle sprains comprise approximately 6 percent of acute ankle sprains without fracture. The incidence in the United States is 2.09 injuries per 100,000 person-years [1]. The incidence in United States collegiate American football players is about 2.5 per 10,000 athletic exposures [2,3].

In the general population presenting to an emergency department, 5.7 percent of acute ankle sprains without fracture are high ankle sprains [4]. At the United States Military Academy, 6.7 percent of acute ankle injuries involve the syndesmosis, with an incidence rate of 4.8 per 1000 person-years [5]. A smaller study at the Academy found 16 percent of acute ankle sprains involve the syndesmosis [6]. The incidence reported in other subpopulations varies widely. High ankle sprains comprised 4 percent of all acute ankle sprains among professional English soccer players [7], 24.6 percent among American college football players [8], and 73 percent among professional American hockey players [9]. Other studies confirm the relatively high rates among American football players and participants in other contact sports [2,10], especially wrestling and ice hockey [3]. The high, rigid ankle support of a hockey skate, which transfers forces proximally along the leg, likely plays a role in the higher rate of syndesmotic injury among hockey players, although the actual incidence is unlikely to be as high as that reported in the study cited above.

Among studies using magnetic resonance imaging (MRI) to evaluate injury patterns, prospective studies of acute ankle injuries without fracture presenting to emergency departments reported syndesmotic injuries in 8 to 13 percent of injuries [11,12]. In other subpopulations, the proportion of acute ankle injuries with syndesmotic injury varies from 20 to 60 percent [13,14]. This wide range is likely due to inconsistencies in the literature related to the different subpopulations studied. As examples, some studies have looked only at winter athletes while others include only patients with "severe" ankle sprains.

Risk factors for high ankle sprain in athletes include sports competition (higher rate than practice) [15], male sex (2.25- to 3-fold risk) [16] and intercollegiate sport participation (2.4-fold risk) [5,15]. Whether playing surface contributes to injury risk remains unclear [15]. Of major sports, American football, basketball, football (soccer), and lacrosse are most commonly involved [10,15]. Game play conferred a 14-fold risk compared with practice among American college football players, among whom 75 percent of injuries involved contact with another player [8]. Winter sports involving use of skis and skates may increase risk [9,13], presumably due to the high-energy external rotation forces exerted on the lower leg.

CLINICAL ANATOMY AND BIOMECHANICS — The bony ankle joint is comprised of the tibia and fibula articulating with the talus. Together the tibia and fibula comprise the ceiling, or "plafond," of the ankle joint, and the notch formed by this ceiling and the medial and lateral malleoli is called the mortise. Approximately 85 percent of body weight is supported by the tibia and the remainder by the fibula. Ligamentous stability is provided proximally by the ligaments comprising the tibiofibular syndesmosis (figure 1 and picture 1); laterally by the anterior talofibular ligament, calcaneofibular ligament (CFL), and posterior talofibular ligament (PTFL) (figure 2 and figure 3); medially by the broad deltoid ligament (figure 4 and figure 5); and circumferentially by the joint capsule. Ankle anatomy is reviewed in greater detail separately; the tibiofibular syndesmosis and other structures of direct relevance to high ankle sprains are discussed below. (See "Ankle fractures in adults", section on 'Clinical anatomy' and "Non-Achilles ankle tendinopathy".)

A syndesmosis is defined as a fibrous joint formed by two adjacent bones linked by strong membranes or ligaments (figure 6). The distal lateral tibia has a concavity of varying depth—the incisura tibialis—that houses the convex distal medial fibula. The tibiofibular contact zone is 3 to 9 mm long and 2 to 5 mm wide, and each surface is covered with thin hyaline cartilage continuous with that of the plafond. The distal or inferior tibiofibular syndesmosis is comprised of four ligamentous structures: the anterior inferior tibiofibular ligament (AITFL; sometimes referred to as the anterior tibiofibular ligament), the posterior inferior tibiofibular ligament (PITFL; sometimes referred to as the posterior tibiofibular ligament), the transverse ligament, and the interosseous membrane (IOM).

The wide, trapezoid-shaped AITFL is located immediately superior to the anterior mortise and traverses obliquely in a posteroinferior orientation from the tibia to the fibula. Approximately 20 percent of the inferior edge of the ligament is intraarticular. The similarly shaped PITFL is located immediately superior to the posterior mortise and traverses obliquely anteroinferiorly from the tibia to the fibula. Its lower part, the transverse ligament, is considered a separate structure and is a round, thick ligament that runs more horizontally from tibia to fibula. The IOM is of variable size and can be absent in some persons. It spans from tibia to fibula along a 2-cm length, lying between the AITFL and PITFL and blending into both [17].

The syndesmosis provides proximal stability to the ankle joint. It is strong but not completely rigid and normally has a small degree of motion. The IOM is more elastic and may act as a "spring" giving the syndesmosis slight flexibility during the late-stance phase of walking when the foot is dorsiflexed, bringing the widest part of the talus into the ankle mortise. The other ligaments provide more rigid stability at the endpoints of this movement [17]. The AITFL provides approximately 35 percent of this stability, 33 percent is provided by the transverse ligament, 22 percent by the IOM, and 9 percent by the PITFL [18]. When the ankle is fully dorsiflexed, the syndesmosis is placed in tension, and when external rotation is added to this, these ligaments are placed at greater risk of rupture.

MECHANISM OF INJURY — High ankle sprains typically occur during high-intensity athletic activities such as competitive American football, rugby, basketball, soccer (football), lacrosse, hockey, and other contact or collision sports, and downhill skiing. Player contact accounts for 46 to 75 percent of high ankle sprains [15]. An external rotation or eversion force applied to a dorsiflexed ankle is the most common mechanism. This can happen when the leg is rotated forcefully against a planted foot or toe. Most such injuries occur during contact with other athletes either when the athlete is standing and the foot is forced into dorsiflexion and external rotation (figure 7), or when the athlete is prone on the ground and another athlete steps or lands on their posterior leg while the foot is externally rotated [19]. Other possible mechanisms may include abduction (lateral shift) or eversion (lateral tilt) of the foot, or hyper-dorsiflexion at the ankle [20].

In all mechanisms, the lateral force of the talus pressed against the distal fibula applies tension across the syndesmosis. This tension causes a sequence of injuries depending upon the degree of force involved. Rupture of the anterior inferior tibiofibular ligament (AITFL) is the first injury, followed by a tear of the IOM, and, rarely, the posterior inferior tibiofibular ligament PITFL. If the force causing the injury is sufficiently great, there may also be disruption of the deltoid ligament medially, a spiral fracture of the proximal fibula (Maisonneuve fracture (image 1)), or both. In cadaver studies where the syndesmotic ligaments are sectioned and the foot placed in various positions of stress, isolated AITFL rupture resulted in the fibula externally rotating and sometimes displacing posteriorly [21]. However, weight-bearing did not increase the degree of displacement in these studies.

CLINICAL PRESENTATION AND EXAMINATION

History — The patient with a high ankle sprain typically describes a clear injury to the ankle. Some may recall a mechanism involving forceful external rotation or eversion of a dorsiflexed ankle, as described immediately above. In an observational study with 26 high ankle sprains, an ankle eversion mechanism correlated closely with syndesmotic injury [22]. Pain is usually focused along the anterolateral ankle but may be more diffuse and severe if medial ligaments are disrupted. Athletes with milder injuries may be able to continue playing through the pain, but often with reduced speed and agility. Those with more severe injuries are usually unable to continue sport activity due to severe pain with weight bearing.

Physical examination — On examination, common findings in patients with a high ankle sprain include antalgic gait or inability to bear weight, lateral and possibly anterior ankle edema, as well as tenderness over the anterior tibiofibular ligament (AITFL) (picture 2 and picture 3) and possibly more proximally along the interosseous membrane (IOM). According to a small prospective study using MRI as the gold standard, local tenderness over the syndesmosis ligaments had a sensitivity of 92 percent and specificity of 29 percent for syndesmotic injury [23]. Medial and lateral ankle ligaments may be tender depending on the extent of injury.

Bony tenderness may indicate fracture. At a minimum, bony palpation should include the proximal fibula, distal tibia and fibula, and talus. In patients with severe pain and disability, it is reasonable to obtain plain radiographs to assess for fracture prior to performing any further examination maneuvers.

To the extent possible based on the patient's symptoms and injuries, ankle range of motion and strength should be assessed in all planes of ankle motion (dorsiflexion, plantarflexion, inversion, and eversion). Stability testing should include tests of the lateral ankle ligaments, including the drawer test for the anterior talofibular ligament (picture 4) and the talar tilt test for the calcaneofibular ligament (CFL) (picture 5). Neurovascular status should be assessed to determine the presence of complications and associated conditions.

Tests of the syndesmosis include the single-leg hop, squeeze, dorsiflexion-external rotation, Cotton, and fibular translation tests. Systematic reviews of clinical tests for ankle syndesmosis injury found that clinicians cannot rely on any single diagnostic maneuver to definitively diagnose syndesmosis injury [24,25]. However, a prospective, blinded study of 87 patients with acute syndesmosis injury confirmed by magnetic resonance imaging (MRI) showed that a combination of sensitive signs (tenderness over the AITFL, inability to perform a single-leg hop, and a painful dorsiflexion-external rotation test) plus one specific sign (painful squeeze test) resulted in a high degree of diagnostic accuracy [23]. We believe that performing this combination of four tests is a sensible approach to the examination when syndesmotic injury is a major consideration. However, if this approach is unrevealing but clinical suspicion remains high, it is best to perform diagnostic imaging.

Special tests

Dorsiflexion-external rotation test — The dorsiflexion-external rotation test reproduces pain at the syndesmosis by recreating the forces involved in a common mechanism of injury (picture 6). It is performed with the patient seated and the leg hanging off the examination table at a 90-degree angle. The leg is stabilized by grasping the upper calf or front of the knee with one hand. The other hand grasps the foot, dorsiflexes the ankle to its endpoint, and then gently but firmly externally rotates the foot. During foot rotation the knee should remain facing forward. Pain reproduced at the AITFL location is considered a positive test [19,24,26]. In isolation, this maneuver showed a sensitivity of 71 percent and specificity of 63 percent in a prospective study of 87 patients of whom 38 had a syndesmotic injury [23]. It is best used in conjunction with another sign with high sensitivity, such as localized tenderness over the AITFL, to "rule out" a syndesmosis injury if the test is negative.

Squeeze test — The squeeze test attempts to reproduce pain at the syndesmosis. It is performed with the patient seated and the leg hanging off the examination table at a 90-degree angle (picture 7). The examiner squeezes the upper half of the calf in an anteromedial-to-posterolateral direction. Biomechanically, this maneuver causes widening of the distal tibiofibular space. Pain reproduced at the AITFL location is considered a positive test [20,27]. In isolation, this test showed a sensitivity of 26 percent and specificity of 88 percent in a prospective study of 87 patients of whom 38 had a syndesmotic injury [23]. Given its high specificity, it is best used to "rule in" a syndesmosis injury after other signs with higher sensitivity are found to be positive.

Other tests include fibular translation and talar translation maneuvers. However, these examination tests have not been rigorously tested for sensitivity, specificity, or clinical accuracy [28] and have poor interrater reliability [24], and therefore are not recommended.

DIAGNOSTIC IMAGING

Approach to imaging — Standard plain radiographs of the ankle (image 2) are recommended for the evaluation of suspected high ankle sprains due to the association of this injury with joint instability. In acute ankle injury, the Ottawa criteria should be used to determine who warrants evaluation with radiographs. However, regardless of these criteria, if the dorsiflexion-external rotation test is performed prior to imaging and elicits pain, indicating possible syndesmotic injury, plain radiographs should be obtained because a positive test is associated with ankle fracture and diastasis may be apparent on radiograph [29]. Guidance about the views to obtain and how to assess them is provided below. (See "Ankle sprain in adults: Evaluation and diagnosis", section on 'Ottawa ankle rules' and 'Plain radiographs' below and 'Dorsiflexion-external rotation test' above.)

If plain radiographs identify diastasis (see 'Plain radiographs' below) between the distal tibia and fibula but no fracture, a grade 3 syndesmotic injury is present and the patient is referred to an orthopedic surgeon for management. (See 'Injury grade' below and 'Indications for orthopedic consult or referral' below.)

If plain radiographs identify a fracture, the nature of the fracture and any associated soft tissue injury determine management. All unstable injuries and complex fractures require orthopedic referral. The evaluation and management of ankle and leg fractures are discussed separately. (See "Ankle fractures in adults" and "Fibula fractures" and "Tibial shaft fractures in adults" and "Talus fractures".)

The best approach to subsequent imaging for patients with a clinical diagnosis of syndesmotic injury but normal plain radiographs remains unclear and controversial but clinically important, as patients with grade 2 injuries may benefit from surgical repair while those with grade 1 injuries are managed non-operatively. (See 'Distinguishing between grade 1 and grade 2 injuries' below.)

Stress radiographs are of uncertain usefulness; decisions about whether to obtain them should be deferred to surgical consultants. Musculoskeletal ultrasound appears to be an accurate tool for determining injury grade, although published evidence is limited, and study quality depends upon the skill of the clinician performing the examination. Another approach is to forego additional imaging if concern about major injury is relatively low based on the clinical assessment and to allow the patient a trial of conservative therapy following an appropriate period of immobilization. Alternatively, when there is greater concern for a more severe (ie, grade 2) injury or a definitive diagnosis is required (eg, high demand sport or occupation), a magnetic resonance imaging (MRI) study can be obtained. MRI is the best advanced imaging technique for assessing high ankle sprain severity and detecting concomitant injury. However, a clear relationship between MRI findings and clinical outcomes has yet to be established in patients with grade 2 injuries. (See 'Stress radiographs' below and 'Ultrasound (US)' below and 'Magnetic resonance imaging (MRI)' below.)

Computed tomography (CT) may have some value for detecting occult fractures and syndesmotic injury, but it is not as useful as MRI for detecting soft tissue injury [30]. (See 'Computed tomography (CT)' below and 'Ultrasound (US)' below.)

Plain radiographs — When assessing the patient with suspected high ankle sprain, plain radiographs of the ankle should be obtained, including anteroposterior (AP), lateral, and mortise views (image 2). Bilateral weight-bearing views are optimal in order to increase the sensitivity for ligamentous instability, but these may cause too much pain to obtain [31]. AP and lateral views of the entire tibia and fibula should be obtained if there is tenderness proximal to the malleoli. Plain radiographs will detect most ankle and leg fractures but are less sensitive for detecting injuries to the syndesmosis, even when tibiofibular diastasis is present [32].

In addition to identifying fractures, clinicians should assess radiographs carefully for signs of ligamentous instability, which may require surgical management. Widely used but poorly validated parameters (best evaluated on the mortise view (image 3)) are the width of the medial clear space (MCS) (the distance between the medial border of the talus and the lateral border of the medial malleolus measured 5 mm below the talar dome) (image 4 and image 5) and the tibiofibular clear space (TFCS) (the distance between the posterolateral tibia and medial fibula measured 10 mm above the tibial articular surface) (figure 8) [30]. Based on small studies using MRI correlation, a TFCS on a mortise view radiograph greater than 5.3 mm in non-weight-bearing subjects is approximately 82 percent sensitive and 75 percent specific for syndesmotic injury, and a MCS greater than 2.8 mm is approximately 73 percent sensitive and 59 percent specific for syndesmotic injury and instability [12]. Any widening of the MCS should be viewed as significant and likely involves concomitant rupture of the deltoid ligaments (image 4 and image 5). Other indirect findings suggesting syndesmotic injury include avulsion fractures from the anterolateral tibia adjacent to the syndesmosis.

Obtaining comparison radiographs of the uninjured ankle is often helpful. Relative widening of the TFCS of 2 mm or more compared with the uninjured side is suggestive of unstable syndesmotic injury [33]. While absolute distance of the TFCS exceeding 6 mm was traditionally the main determinant of syndesmosis widening [34], this is a poor predictor of syndesmotic injury and need for surgical management, as it can miss up to 57 percent of unstable syndesmotic injuries [35]. There is significant individual and gender variation in the absolute clear space distance in uninjured ankles, so absolute distance is less useful than relative difference [36-38]. Measurement of the tibiofibular overlap is not recommended due to wide variability [33].

Stress radiographs — Plain radiographs of the ankle obtained with the leg externally rotated (ie, stress radiographs) have been described as a method for detecting latent instability of the syndesmotic ligaments. However, several case series have found such imaging to be insensitive for detecting latent diastasis [10,18,20]. In addition, no study performed in live or unanesthetized patients has confirmed that stress testing is more effective for detecting latent instability than weight-bearing films or MRI.

It is difficult to perform stress radiographs in primary care settings, and the author recommends deferring to orthopedic consultants about the need for such imaging. Stress images are obtained by applying a standard external rotation force of 7.5 N to the ankle in neutral position and obtaining an AP or mortise view. Any more than 2 mm of laxity compared with non-stress lateral views of the uninjured side is considered unstable [39]. Anesthetic injection into the painful areas of the ankle is usually required prior to obtaining stress views.

Ultrasound (US) — Given its superficial location, the AITFL is easily visualized with good resolution using US (image 6). US has the advantage of allowing a real-time, dynamic assessment of diastasis when a dorsiflexion-external rotation (DFER) stress is applied to the ankle. In unstable syndesmotic injury, the tibiofibular clear space (TFCS) can be seen to widen during DFER stress, compared with its neutral state. Comparison with the uninjured ankle is easily performed and useful. Performance of the ultrasound examination of the ankle is reviewed separately. (See "Musculoskeletal ultrasound of the ankle and hindfoot".)

A study of 14 patients with MRI-confirmed AITFL sprain reported that static ultrasound was 100 percent sensitive and specific for detecting complete AITFL rupture, and side-to-side comparison during external rotation stress was 86 percent sensitive [40]. Another controlled study (9 injured, 38 controls) showed 100 percent sensitivity and specificity for diagnosis of AITFL rupture compared with MRI when the TFCS of the injured side during DFER was more than 0.9 mm greater than the uninjured side. On just the injured side, a difference of more than 0.4 mm between the measured TFCS in neutral versus DFER stress was 89 percent sensitive and specific [41].

Magnetic resonance imaging (MRI) — MRI is considered the most accurate imaging modality to visualize injury to the syndesmosis, with a sensitivity of 100 percent and specificity of 93 percent for anterior inferior tibiofibular ligament (AITFL) injury, and 100 percent sensitivity and specificity for posterior inferior tibiofibular ligament (PITFL) injury, according to small observational studies [42,43]. In suspected chronic syndesmotic injury, it has slightly lower accuracy [44], but this improves with the addition of gadolinium enhancement [45].

MRI is used to determine the exact injury pattern and grade injury severity, and it has the advantage of visualizing the concurrent injuries present in approximately three quarters of patients with syndesmosis injuries [12,14,31,46]. These include anterior talofibular ligament sprain, calcaneofibular ligament (CFL) sprain, deltoid ligament sprain, occult fractures, bone bruises, talar dome osteochondral lesions, and incongruity of the tibiotalar joint.

Computed tomography (CT) — CT is not the imaging modality of choice when isolated syndesmosis injury is suspected, but it may be obtained if MRI is not available or too costly. CT may be more useful than MRI for characterizing ankle fractures preoperatively and assuring adequate reduction of the tibiofibular relationship intraoperatively. CT does not visualize soft tissues as well as MRI but can detect acute and chronic tibiofibular diastasis of as little as 1 mm [32,47]. We suggest imaging the uninjured contralateral ankle. Due to significant anatomic variation among individuals and genders, a person's uninjured ankle is the best determinant of normal structure [48].

INJURY GRADE

Definitions — There is heterogeneity in the orthopedic literature about the definition of injury grades for high ankle sprains [6,25,31,49-51]. The author suggests the following classification scheme [31]:

●Grade 1 injury – Partial tearing of AITFL, with no diastasis on radiograph, computed tomography (CT), or magnetic resonance imaging (MRI); considered a stable injury.

●Grade 2 injury – Complete tear of AITFL and partial tear of IOM, without diastasis seen on radiograph, CT, or MRI; considered a latently unstable injury. Ultrasound or MRI may be needed in some cases for diagnosis and distinction from grade 1 and grade 3 injuries. Usually involves partial deltoid (medial) ankle ligament injury. (See 'Distinguishing between grade 1 and grade 2 injuries' below.)

Some have proposed subclassifying grade 2 injuries using a combination of MRI findings and clinical signs. Grade 2a injuries involve a ruptured AITFL but no concomitant ligamentous injury on MRI (other than the ATFL) and clinical stability. Grade 2b injuries involve a ruptured AITFL and concomitant injury to the deltoid ligament or PITFL on MRI and clinical signs of instability, such as a positive squeeze test and tenderness extending greater than 6 cm proximal to the ankle joint [52]. (See 'Distinguishing between stable and unstable grade 2 injuries' below.)

●Grade 3 injury – Complete tear of AITFL and IOM plus partial or complete tear of PITFL, with diastasis on radiograph, CT, or MRI; considered an unstable injury. Usually involves concomitant fractures and complete deltoid ligament rupture.

In a prospective series using clinical findings, radiograph, and MRI for diagnosis and severity assessment, 85 percent of syndesmotic injuries without ankle fracture were grade 1, 9 percent were grade 2, and 5 percent were grade 3 [12].

Distinguishing between grade 1 and grade 2 injuries — In patients with a clinically diagnosed syndesmotic injury but negative plain radiographs (no fracture and no diastasis), distinguishing between grade 1 and grade 2 injuries can be difficult but it is important, as patients with grade 2 injuries may benefit from surgical repair while those with grade 1 injuries are managed non-operatively. Evidence directly related to this diagnostic problem is scant and several reasonable approaches may be used.

One option is to refer these patients to an orthopedic surgeon with experience managing syndesmotic injuries.

A second option for clinicians skilled in the performance of musculoskeletal ultrasound is to perform a thorough ultrasound examination including a dynamic assessment to identify whether a complete tear of the AITFL and partial tear of the IOM are present, and then refer to a surgeon if this is the case or to physical therapy if not. Close follow-up by the clinician remains essential.

A third option is to perform serial clinical assessments on a weekly basis - after two weeks of immobilization in a fracture boot - using the single-leg hop test. If after two weeks of immobilization the patient is able to perform a single-leg hop test, a grade 1 injury is diagnosed and the patient managed accordingly. If the patient is unable to perform a single-leg hop test, immobilization is continued for another week. If after three weeks of immobilization the patient remains unable to perform the test, a grade 2 injury is assumed and the patient is either referred to an experienced surgeon or advanced diagnostic imaging, usually MRI, is obtained to determine the extent of injury.

A fourth option for patients felt to be at higher risk for grade 2 injury based on the history and examination, or who require a definitive diagnosis due to the high demands of their sport or occupation, is to obtain an MRI as part of the initial evaluation. Given the limited outcome data pertaining to this subpopulation of patients, there are undoubtedly other good approaches to their evaluation, but all the options described above are reasonable.

Distinguishing between stable and unstable grade 2 injuries — The distinction between stable and unstable grade 2 syndesmotic ankle injuries may be important in athletes because conservative treatment of stable injuries allows for earlier return to play, while conservative treatment of unstable injuries may be inadequate and lead to delayed healing or complications. MRI or arthroscopy is necessary to distinguish clearly between stable and unstable grade 2 injuries.

Using MRI findings, the authors of a prospective study of 64 professional athletes with MRI-proven complete AITFL ruptures distinguished between those who were likely to have instability and require surgical fixation of the syndesmosis and those who were not [52]. Suspected instability (grade 2b), defined as AITFL rupture on MRI with either deltoid ligament injury on MRI or a positive squeeze test, was assessed with arthroscopy – widely considered the gold standard for diagnosis – and if confirmed, treated with fixation. The combination of findings used to define grade 2b injuries correlated closely with unstable injuries identified by arthroscopy and needing fixation (36 of 38 injuries). In contrast, MRI-proven AITFL ruptures associated with an intact deltoid ligament on MRI and a negative squeeze test were deemed stable injuries, and all 26 athletes with these findings did well with conservative management.

DIAGNOSIS

Overall approach — Definitive diagnosis of a high ankle sprain (syndesmotic injury) is made by magnetic resonance imaging (MRI), but this is often unnecessary, and a clinical diagnosis can be made based on the history and examination findings. High ankle sprains are suspected when a person (usually an athlete) sustains an injury by a mechanism involving forced dorsiflexion and external rotation or eversion of the ankle and complains of pain just proximal to the ankle joint. Pain is usually present along the lateral half of the distal leg, but not as distal or lateral as the more common anterior talofibular ligament and calcaneofibular ligament (CFL) injuries. Sensitive findings include inability to perform a single-leg hop, localized tenderness over the anterior inferior tibiofibular ligament (AITFL), and pain at that location induced by the dorsiflexion-external rotation test. Pain at the syndesmosis with the squeeze test is a specific finding. Radiographs are obtained to rule out fracture and frank syndesmotic diastasis. MRI is obtained when a definitive diagnosis is required or the extent of injury must be determined, as concomitant injuries are frequently present. Ultrasound and computed tomography (CT) are useful when MRI is not available. An algorithm summarizing our approach to diagnosis and management is provided (algorithm 1). (See 'Approach to imaging' above.)

Concomitant foot and ankle injuries are common with syndesmotic injury, and clinicians should look carefully for such injuries.

INDICATIONS FOR ORTHOPEDIC CONSULT OR REFERRAL — Orthopedic referral is indicated for grade 2 and grade 3 syndesmosis injuries because the resulting instability is debilitating, may not heal well or rapidly with conservative therapy, and may result in degenerative arthritis if not reduced. Any grade 1 injuries with associated fractures should be referred since they may require operative intervention as well [31] (see 'Injury grade' above).

According to a 2020 systematic review, 2.7 to 4 percent of high ankle sprains require surgery [15].

DIFFERENTIAL DIAGNOSIS — The differential diagnosis of high ankle sprains includes a number of bony and soft tissue injuries. Many ankle fractures have concurrent syndesmotic injury and three quarters of patients with syndesmotic injury who have normal radiographs have a concurrent bony or ligamentous injury.

●Fibular fracture – A lateral malleolar fracture may be sustained concurrently with syndesmotic injury. Tenderness along the posterior margin of the distal 6 cm of the fibula suggests such injury. A proximal fracture of the fibula (Maisonneuve fracture (image 1)) may be a complication of unstable syndesmotic injury. With this injury, the proximal fibula is markedly tender, typically around the fibular neck. Radiographs of the ankle and leg identify these fractures. (See "Ankle fractures in adults" and "Fibula fractures".)

●Tibial fracture – An avulsion fracture of the anterior tubercle of the tibia can accompany unstable syndesmotic injury. The patient will be tender along the anterolateral tibia just proximal to the ankle joint line, adjacent to the anterior inferior tibiofibular ligament (AITFL). This can be detected by ankle radiograph in most cases, or by computed tomography (CT) or magnetic resonance imaging (MRI). (See "Overview of tibial fractures in adults".)

●Talar fracture – Fracture of the talar head, neck, or dome causes deep ankle pain. In head and neck fractures, tenderness is present at the dorsal midfoot at or distal to the tibiotalar joint line. With talar dome fractures, tenderness may be present at the joint line, or the fracture may be too deep to palpate, but an ankle effusion is typically present. Plain radiographs often reveal these fractures but miss a significant number. If talar fracture is suspected despite negative radiographs, CT or MRI should be obtained. (See "Talus fractures".)

●Anterior talofibular ligament (ATFL) sprain – Inversion ankle injuries cause most ATFL sprains, in contrast to the external rotation mechanism that produces high ankle sprains. However, these injuries can occur concomitantly. With ATFL sprains, maximal tenderness is present at the anterolateral ankle but more distal than with syndesmotic injury: just distal to the tibiotalar joint line at the anterior aspect of the lateral malleolus (picture 3). There is usually significant swelling and sometimes ecchymosis of the lateral ankle with ATFL injuries, whereas isolated high ankle sprains typically have minimal swelling. High-grade ATFL injury causes laxity with ankle drawer testing (picture 4). Resting or standing ankle radiographs do not reveal instability. (See "Ankle sprain in adults: Evaluation and diagnosis", section on 'Special tests'.)

●Calcaneofibular ligament (CFL) sprain — Inversion injury accounts for most CFL injuries. Tenderness is present at the lateral ankle just distal to the lateral malleolus. Concurrent ATFL injury is likely, and typically there is marked swelling and often ecchymosis at the lateral ankle. High-grade CFL injury causes laxity with inversion testing (talar tilt test (picture 5)). Resting or standing ankle radiographs do not reveal instability. (See "Ankle sprain in adults: Evaluation and diagnosis", section on 'Special tests'.)

●Posterior talofibular ligament (PTFL) sprain – Severe inversion ankle sprains may injure the PTFL. Tenderness is present at the posterolateral ankle. Concurrent sprain of the ATFL and CFL is likely, so significant swelling and likely ecchymosis too are found at the lateral ankle, in contrast to the minimal swelling associated with isolated high ankle sprains. Instability may be present with the drawer and talar tilt tests.

●Deltoid ligament sprain – Deltoid ligament sprains may occur in isolation or concurrently with syndesmotic injury. A mechanism involving ankle eversion is more likely to produce an isolated injury, whereas an external rotation mechanism that injures the syndesmosis is more likely to rupture the anterior portion of the deltoid ligament as well. Tenderness is present at the medial ankle just distal to the medial malleolus. Any widening of the medial clear space on mortise view radiographs suggests deltoid ligament rupture (image 4 and image 5). (See "Ankle sprain in adults: Evaluation and diagnosis".)

●Anterior ankle impingement – Injury to an intra-articular accessory ligament of the AITFL, called Bassett's ligament, can cause pain in the anterolateral ankle similar to syndesmosis injury. An ankle inversion mechanism is more likely to cause this injury, rather than external rotation, and it is generally associated with much less pain than a high ankle sprain. Tenderness may occur in the same location as the syndesmosis but is more often isolated to the joint line just at or distal to the AITFL. Pain is reproduced by forced ankle dorsiflexion, which impinges the injured Bassett's ligament between the talus and ankle plafond. No signs of instability of the syndesmosis are apparent on radiographs. Definitive diagnosis is by MRI or arthroscopy, and treatment is surgical excision of the accessory ligament [53].

●Bone bruises – Bone bruises can occur as isolated injuries from nearly any mechanism of ankle injury, or can develop concurrently with high ankle sprains. Focal bony tenderness (fibula, talus, tibia) with negative radiographs suggests the diagnosis. When necessary, MRI is the definitive method for establishing the diagnosis.

●Acute compartment syndrome – Severe injuries of the leg or calf, such as crush injuries, fractures, or severe contusions, can cause marked swelling within a soft tissue compartment that may compromise normal neurovascular function. This limb-threatening condition is termed acute compartment syndrome and it is a surgical emergency. ACS can develop in any of the leg compartments: anterior, lateral, deep posterior, or superficial posterior (figure 9). Findings associated with ACS include pain out of proportion to the injury, paresthesias, pain with passive stretch of the muscles in the affected compartment (eg, by passively flexing and extending the toes or ankle), and a palpably tense compartment. Imaging may detect various injuries but is not diagnostic for ACS. If ACS is suspected, immediate consultation with orthopedic surgery should be obtained for evaluation and likely measurement of compartment pressures. (See "Acute compartment syndrome of the extremities".)

INITIAL TREATMENT

Overview — Grade 1 injuries are managed conservatively with immobilization for one to three weeks followed by gradual return to activity, while grade 2 and grade 3 injuries require evaluation for possible operative management. An algorithm summarizing our approach to diagnosis and management is provided (algorithm 1).

Concomitant fractures — Syndesmotic injuries concurrent with ankle fractures should be splinted and referred urgently to an orthopedic consultant. Syndesmotic instability is treated with reduction of the fibula and surgical fixation.

Syndesmotic injuries without fractures — All syndesmotic injuries should be treated initially with splinting and non-weight-bearing. Early treatment for injuries of all grades should include PRICE-M (protection, rest, ice, compression, elevation, and medication) for the first two to four days:

●Protection is achieved optimally with a posterior leg splint (figure 10), as it prevents excessive dorsiflexion and is easier to don than a fracture boot, although a fracture boot may be used. (See "Basic techniques for splinting of musculoskeletal injuries", section on 'Posterior leg splint'.)

●Rest is achieved by non-weight-bearing using crutches.

●Ice – Cryotherapy applied as ice or cold water immersion is recommended for 15 to 20 minutes every two to three hours for the first 48 hours, or until swelling is improved – whichever comes first.

●Compression with an elastic bandage to minimize swelling should be applied early.

●Elevation – The injured ankle should be kept elevated above the level of the heart to further alleviate swelling.

●Medication – A short course of nonsteroidal antiinflammatory drugs (NSAIDs) and/or acetaminophen can be used for analgesia as needed.

High-grade syndesmotic injuries — Grade 2 and grade 3 syndesmotic injuries without fracture should be treated initially as described immediately above and referred urgently (within five to seven days) for possible operative management [31]. These injuries are uncommon without concomitant fracture, and research is extremely limited, but expert opinion strongly favors surgical treatment of grade 2 and grade 3 syndesmosis injuries. Some grade 2 injuries may be stable enough for conservative management [52], but we recommend that this determination be made only by clinicians skilled in the evaluation and treatment of such ankle injuries. (See 'Injury grade' above.)

FOLLOW-UP CARE

Immobilization — In five to seven days, patients with grade 1 injuries should be seen and reexamined. By this time, most swelling has resolved and more definitive protection or immobilization can be used. The patient should be immobilized initially with a removable fracture boot that prevents any ankle motion, using crutches for non-weight-bearing or partial weight-bearing as determined by pain and the clinical scenario, for one to three weeks [50,51].

Rehabilitation — Once partial weight-bearing is painless, the patient may progress to full weight-bearing. Weekly follow-up with the treating physician is recommended in order to determine the earliest safe time to discontinue immobilization. Once the fracture boot is discontinued, we suggest early referral to physical therapy to expedite functional recovery. However, protection should be maintained for several weeks using an off-the-shelf stirrup brace or articulated ankle-foot orthosis during weightbearing activity until full function is regained.

High quality evidence pertaining to physical therapy for syndesmotic injury is limited, but one prospective observational study involving 60 consecutive high level United States collegiate athletes with a clinical diagnosis of high ankle sprain describes the aggressive, accelerated implementation of a standard treatment protocol that resulted in a rapid return to play (average 13.4 days) [10]. All participants had radiographs showing no fracture or diastasis, and the rehabilitation program required close supervision in the training room. Athletes were immobilized and kept non-weight-bearing for only four days. On days 4 to 5 they began partial weight-bearing while protected with an ankle brace and performed range of motion, isometric strength, and light proprioceptive exercises. From day 6 onward they performed full weight-bearing and continued progressive motion, strength, and proprioceptive exercise. When they were able to perform 10 single-leg hops on their toes without noticeable difficulty, they were allowed to begin progressive functional and sport-specific training while protected in an ankle splint. During their return to sport, athletes had their ankles taped and wore an ankle splint for protection. Fifty-three of the 60 athletes treated were polled six or more months after injury, and 66 percent rated their outcome as "excellent," while the other 34 percent rated it as "good."

Surgical treatment — Those patients with acute grade 2 or grade 3 injuries treated with surgery undergo reduction of the syndesmosis and fixation with cortical screws or suture buttons. Surgical technique depends on any concomitant fractures, concomitant ligament injuries (eg, deltoid ligament), surgeon preference, and patient needs [51,54]. Subacute injuries (six weeks to six months) with instability typically undergo ligament reconstruction and syndesmosis fixation, whereas chronic injuries (older than six months) are often treated with syndesmotic fusion [54]. Rehabilitation after surgical management should be determined by the surgeon and physical therapist.

COMPLICATIONS AND PROGNOSIS — If not treated with surgical reduction, grade 2 and grade 3 injuries are associated with high rates of chronic, painful disability (eg, painful push-off, ankle swelling and stiffness) and increased risk of degenerative arthritis of the tibiotalar joint [31].

Heterotopic ossification (HO) at the syndesmosis has been noted on plain radiographs at late follow-up of high ankle sprains. However, evidence is limited and the reported incidence at least six months after a grade 1 sprain ranges from 2 [10] to 50 [20] to 90 percent [55]. No difference in ankle function or symptoms at long-term follow-up was noted in one small retrospective study of patients who developed HO, but ankles with HO were associated with higher rates of recurrent lateral ankle sprain [55].

Chronic ankle symptoms such as pain, stiffness, and swelling occur in approximately 20 to 40 percent of patients, even after a grade 1 high ankle sprain [6,55]. However, ankle function is rated as "excellent" or "good" in the large majority of patients [10,55].

RETURN TO SPORT OR WORK — Compared with most lateral ankle sprains, syndesmotic injury, whether isolated or concomitant with an ankle fracture, causes a significant delay in return to sport [56]. In a 2022 meta-analysis, the mean time for return to sport was 52 days, with an average of 39.3 days in patients treated nonsurgically and 70.9 days in those requiring surgical repair. Despite these delays, the overwhelming majority of athletes fully recover and resume their previous level of play [57-59].

Grade 1 sprains treated conservatively — Recovery from a high ankle sprain takes two to four times as long as the more common lateral ankle sprain. Return to work or play generally requires two to nine weeks for conservatively treated grade 1 high ankle sprains, depending upon the severity of injury, compliance with physical therapy, and other factors [8-10,20,46,55,60,61].

According to a retrospective study of foot and ankle injuries among collegiate American football players using a national database, the average time needed to return to play (RTP) was 12.0 days in players with partial tears (grade 1 injury) [3]. In a prospective study of 20 Division I American collegiate football players with clinically diagnosed, stable, high ankle sprains, the mean time for RTP was 15.5 days (range 2 to 30 days) [62]. If ultrasound showed an intact AITFL, RTP averaged 3.3 days; if ultrasound showed a ruptured AITFL, RTP averaged 19 days. Length of tenderness along the interosseous membrane (IOM) also correlated with RTP, with players whose tenderness extended more proximally requiring more time before RTP.

Close supervision by athletic trainers or physical therapists and frequent follow-up likely minimizes the time needed for recovery. Treatment must be individualized based upon response to treatment. Criteria for return to full sport or heavy labor include the following:

●Minimal or no tenderness

●Full ankle range of motion

●Ankle and leg strength that is at least 90 percent of the uninjured extremity

●No instability during single-leg hops and lunges

●Ability to complete sport-specific functional testing

Patients should be reassured that some pain, swelling, and stiffness is likely to persist for several months.

Magnetic resonance imaging (MRI) was found to be useful in predicting practices and weekly games lost in a retrospective review of 36 professional American football players (National Football League) with syndesmotic injuries, but without radiographic diastasis, who were treated conservatively. Players with involvement of only the anterior inferior tibiofibular ligament (AITFL) missed two practices and 0.25 games on average. Players with involvement of the AITFL and IOM missed 8.2 practices and 1.6 games. Players with injured AITFL, IOM, and posterior inferior tibiofibular ligament (PITFL) missed 21.1 practices and 3.8 games. The extent of injury (partial versus complete) for each ligament was not specified; however, all three players with triple-ligament injury underwent surgery at the end of their season [46].

Grade 2 and grade 3 sprains — Recovery from surgically treated grade 2 or grade 3 injuries depends upon the presence of concomitant fractures or ligamentous injuries. Isolated grade 2 and grade 3 syndesmotic injuries are uncommon, and data on their postsurgical outcomes are extremely limited. One series of professional athletes with isolated, stable (grade 2a) injuries (ruptured AITFL but intact deltoid ligament on MRI and negative squeeze test) reported return to sport after a mean of 45 days (range 23 to 63) following conservative treatment [52]. Return to sport has averaged 64 [52,63] to 103 days [64] in professional athletes with unstable (grade 2b) injuries (ruptured AITFL and deltoid ligament injury on MRI and positive squeeze test).

Surgical options include cortical screws, suture buttons, and hybrid approaches. Fractures repaired with cortical screws usually require hardware removal at three months postoperation [31], whereas those with suture button usually do not need hardware removal. Due to these advantages, suture-button fixation is becoming more widely used in elite athletes and laborers requiring rapid return to work [50]. Nevertheless, decisions about the best surgical approach vary by clinical circumstance and local expertise and are best made after discussion between the surgeon and patient.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Ankle sprain".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: How to use crutches (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Epidemiology and anatomy – A syndesmotic ankle sprain (ie, high ankle sprain) is an injury to one or more of the ligaments comprising the distal tibiofibular syndesmosis. Syndesmotic ankle injury is much less common than the typical ankle sprain but is associated more often with significant morbidity and the need for surgical treatment. Syndesmotic injury is more common among athletes playing high level sport. Participants in American football and ice hockey appear to be at increased risk. Relevant ankle anatomy is reviewed in the text. (See 'Epidemiology and risk factors' above and 'Clinical anatomy and biomechanics' above.)

●Mechanism of injury – Syndesmotic ankle injury typically occurs during high-intensity athletic activities such as American football, soccer (football), ice hockey, and other contact sports, and downhill skiing. An external rotation force applied to a dorsiflexed ankle is the most common mechanism. This can happen when the leg is rotated forcefully against a planted foot or toe. Most injuries occur during contact with other athletes either when the athlete is standing and the foot is forced into dorsiflexion and external rotation (figure 7), or when the athlete is prone on the ground and another athlete steps or lands on their posterior leg while the foot is externally rotated. (See 'Mechanism of injury' above.)

●History and examination – Pain is usually focused along the anterolateral ankle but may be more diffuse and severe if medial ligaments are disrupted. Athletes with severe injuries are usually unable to continue activity due to severe pain with any weight bearing. Common findings include antalgic gait or inability to bear weight, lateral and possibly anterior ankle edema, and tenderness over the anterior inferior tibiofibular ligament (AITFL) (picture 2 and picture 3) and possibly more proximally along the interosseous membrane (IOM). Sensitive signs for syndesmotic injury include tenderness over the AITFL, inability to perform a single-leg hop, and a painful dorsiflexion-external rotation test. A painful squeeze test is a specific finding (picture 7). (See 'Clinical presentation and examination' above.)

●Diagnostic imaging – Plain radiographs of the ankle are the initial studies obtained if a syndesmotic injury is suspected. If plain radiographs identify a fracture or diastasis between the distal tibia and fibula but no fracture (ie, grade 3 syndesmotic injury), the patient is referred to an orthopedic surgeon. The best approach to subsequent imaging for patients with a clinical diagnosis but normal plain radiographs remains controversial.

Stress radiographs are of uncertain usefulness and decisions whether to obtain them should be deferred to surgical consultants. Musculoskeletal ultrasound appears to be accurate for determining injury grade. When there is concern for a severe injury, a magnetic resonance imaging (MRI) study is the best technique for assessing sprain severity and detecting concomitant injury. (See 'Injury grade' above and 'Diagnostic imaging' above and 'Approach to imaging' above.)

●Diagnosis – An algorithm summarizing our approach to diagnosis and management is provided (algorithm 1).

Definitive diagnosis is made by MRI, but this is often unnecessary, and a clinical diagnosis can generally be made based on the history and examination findings. Distinguishing between grade 1 (partial tear of AITFL; treated conservatively) and grade 2 (complete tear of AITFL; generally treated surgically) injuries can be difficult. Evidence pertaining directly to the evaluation of these injuries is limited and any of several reasonable approaches may be used. These are described in the text. (See 'Distinguishing between grade 1 and grade 2 injuries' above and 'Diagnosis' above.)

●Indications for surgical referral – Referral to a knowledgeable orthopedic surgeon is indicated for grade 2 and grade 3 syndesmosis injuries and any grade 1 injury associated with a fracture. (See 'Indications for orthopedic consult or referral' above and 'Injury grade' above.)

●Differential diagnosis – The differential diagnosis for syndesmotic injury includes ankle fracture (eg, fibula, tibia, talus), ligament sprain (eg, ATFL, CFL, PITFL, deltoid), anterior ankle impingement, and acute compartment syndrome of the leg (a surgical emergency). Key clinical features that help to distinguish among these diagnoses are provided in the text. (See 'Differential diagnosis' above and "Acute compartment syndrome of the extremities".)

●Management – Basic initial care, including non-weightbearing, is provided for all injuries. Subsequent management depends upon the extent of injury (algorithm 1). Isolated grade 1 injuries are treated with physical therapy; injuries of grade 2 or 3 and those associated with fractures or other significant soft tissue injury are referred to an orthopedic surgeon. (See 'Initial treatment' above and 'Follow-up care' above and 'Return to sport or work' above.)