Ankle Dislocation

Etiology

The mechanism of ankle dislocation depends on whether it is associated with a fracture. A pure ligamentous dislocation has been reported to occur in multiple directions and by multiple mechanisms.[3] The most common injury pattern occurs when the ankle is maximally plantarflexed under axial load and forced into inversion.[4] This mechanism allows for anterior extrusion of the talus through the mortise and predisposes the ankle to damage and rupture of the anterior talofibular and calcaneofibular ligaments, leading to a posteromedial dislocation, which is the most common direction of dislocation in pure ankle dislocation. Cadaveric studies by Fernandes recreated this injury by placing the foot in maximum plantar flexion and applying stress in inversion or eversion. This subsequently resulted in a medial or lateral ankle dislocation without fracture and damage to the anterior talofibular and calcaneofibular ligaments.[3][5] Superior dislocation usually results when an everted foot is dorsiflexed. This leads to rupture of the tibiofibular syndesmosis, which, in turn, causes superior dislocation of the ankle joint.[1] Predisposing factors reported include weakness of the peroneal muscle, previous strains, ligamentous laxity, and shortness of the medial malleolus.[3][6]

The more common ankle fracture-dislocation occurs via similar mechanics as non-dislocated ankle fractures. The most likely fractures, bimalleolar and trimalleolar, often result from an abduction force and talus displacement, which is how the ankle appears to be dislocated at the time of evaluation. Sometimes these dislocations spontaneously reduce, leaving a malleolus fracture. These resulting ankle fractures are often classified according to the Lauge-Hansen classification system, which includes 4 types based on the position of the foot and direction of the force.[7] The 4 types include supination-adduction, supination-external rotation, pronation-abduction, and pronation-external rotation. Each of these types has a characteristic malleolar fracture; however, the intra- and inter-observer reliability of this classification system has been called into question in the literature.[8][9]

Epidemiology

A pure ankle dislocation without a concomitant fracture is exceedingly rare. The estimated incidence of pure ankle dislocation occurs in about 0.065% of the presentations of all ankle injuries, which includes soft tissue injuries of the ankle. This amounts to about 0.5% of all ankle dislocations, with over 99% being fracture-dislocations (note that the incidence of this injury may be underestimated given the likelihood of ankle reduction in the community without hospital involvement).[1] Tibiotalar dislocations have been shown to occur concomitantly in 21-36% of ankle fractures.[10][11] The injury most commonly occurs in males (72%) and is usually secondary to sporting accidents (31%) or motor vehicle accidents (30%). The direction of the dislocation is most commonly posteromedial (46%).[1] Rarely, irreducible ankle fracture-dislocations may be encountered due to the interposition of soft tissue or fracture fragments. The “Bosworth Fracture” has been described and occurs when the proximal fibular shaft is locked behind the tibia. This type of injury is often missed on plain x-rays and is not amenable to a closed reduction in the emergency department.[12]

History and Physical

Frequently, the patient presents with a dislocated foot relative to the tibia. All of these injuries benefit from appropriate analgesia and rapid realignment of the foot and ankle to proper anatomic position. If this is not done relatively quickly, the resulting skin breakdown and formation of fracture blisters can then lead to loss of skin coverage of the joint and permanent disability. After attending to other life-threatening injuries following the usual trauma protocols, an ankle dislocation should be reduced, preferably with procedural sedation, although an intra-articular block may be sufficient. Salen et al performed a study in which ankle dislocations were among the most common types of dislocation requiring procedural sedation.[13] While it may be quick to reduce, it is imperative to understand the significant pain that the patient is likely experiencing and to administer appropriate analgesia before any manipulation. Be aware that the vast majority of these injuries, particularly those with open fractures, require operative intervention. An orthopedic consultant should be notified of any open fracture, dislocation with vascular or sensory compromise, bimalleolar fracture, trimalleolar fracture, syndesmotic disruption, or pilon fractures (distal tibial impaction). 

On examination, it is important to note the direction of the foot relative to the ankle mortise, the presence/absence of the dorsalis pedis and posterior tibial pulses, capillary refill of the distal foot, other associated injuries of the foot, and localizing areas of tenderness and swelling. The sensory exam should include the dorsum of the foot, the lateral and medial aspects of the foot, and sensation just proximal to the great and second toes, the area of the innervation of the deep peroneal nerve. The examiner should also note the ability to flex and extend the toes. These important physical exam findings should be documented before and after the manipulation of the foot.[14]

Evaluation

Plain x-rays should be obtained of both the ankle and tibia-fibula before an attempted reduction maneuver. Three views of the ankle should be obtained, including anteroposterior, lateral, and Mortise views. The Mortise view is obtained by aiming the x-ray beam in an anteroposterior direction while internally rotating the ankle 15 degrees. Obtaining full-length tibia-fibula x-rays is imperative to identify Maisonneuve-type injuries (transfer of energy through the interosseous membrane resulting in a proximal fibula fracture or proximal tibiofibular joint dislocation).

Occasionally, reduction may be necessary before imaging is obtained in cases of skin tenting or neurovascular compromise; however, Hastie et al observed a significantly higher rate of re-manipulation (44% before x-ray vs 18% after x-ray; p=0.03).[15]

In a pilon-type fracture, a computed tomography scan may be warranted. An orthopedic surgeon should be consulted before a computed tomography scan, as a fracture requiring temporizing external fixation should be imaged after it is completed for proper preoperative planning.

Treatment / Management

The ankle can be dislocated in 5 directions: anteriorly, posteriorly, laterally, medially, or superiorly. These descriptions describe the position of the talus when compared to the distal tibia. The first 4 dislocations can often be easily reduced while in the emergency department with procedural sedation. A superior dislocation usually results in a pilon fracture and, as stated above, requires orthopedic consultation. Both procedural sedation and intra-articular hematoma block are excellent options for reduction, and in ankle fracture-dislocations, intra-articular hematoma block can be considered as a first-line agent.[16]

The treatment goal is to obtain anatomic alignment of the distal tibia and fibula, with a congruent tibiotalar joint on the AP, lateral, and mortise views of the ankle. When properly reduced, the wider portion of the talar dome should be located back within the ankle mortise. The foot should be at neutral dorsiflexion on the lateral view with a fully congruent talar dome-distal tibia relationship.

Reduction of an ankle dislocation ideally requires 2 providers for the reduction and a single practitioner for procedural sedation, if available; however, a modified Quigley maneuver has been described that allows single-provider reduction and splinting.[17] This reduction maneuver relies on first flexing the knee to relax the gastrocnemius complex, then accentuating the existing deformity, followed by gentle traction, and finally applying a directional force opposite to the original injury. Specific maneuvers are discussed below.

Reduction of an anterior dislocation is performed in the following manner:

1. Slightly flex the knee.
2. While grasping the forefoot with 1 hand and the heel with the other, dorsiflex the foot to accentuate the deformity to disengage the talus.
3. While an assistant provides countertraction on the leg, apply direct traction to the foot and heel to extend the leg and move the foot and talus back into position between the tibia and fibula.

Reduction of a posterior dislocation is accomplished in the following manner:

1. Flex the knee.
2. While an assistant provides counter traction on the leg, grasp the heel with 1 hand and the dorsal metatarsals with the other.
3. Slightly plantar-flex the foot to disengage the talus.
4. Follow this by pulling on the foot with both the dorsum and heel (elongating the leg) while sliding the talus anteriorly into position. It may be necessary to have a second assistant put downward pressure on the tibia and fibula while the foot is pulled forward into position.

Reduction of a lateral or medial fracture-dislocation utilizes these same principles but requires manipulation of the foot by rotating the toes medially or laterally, respectively, into anatomic position so that the patella and foot are pointing in the same direction. Again, verify sensation, palpable pulses, toe movement, and capillary refill.

When the foot is properly reduced, apply a posterior splint and an associated U-shaped splint (stirrup). Make sure to verify movement of the toes, palpable pulses, capillary refill, and sensation of the foot after manipulation and splinting, as well as confirming correct anatomic alignment using post-reduction radiographs. Be sure that your orthopedic consultant is aware of any manipulation that has been performed and is available to definitively manage the fractures associated with the dislocation.[18]

Simple ankle dislocations with concentric reduction can often be managed nonoperatively. Initial management regarding the type of immobilization and weight-bearing status is controversial and often depends on ankle stability noted on exam. There have been reports ranging from early weight-bearing in a CAM walker to 6 weeks of immobilization in a cast, followed by progressive weight-bearing.[1][19] If the patient continues to have pain and feelings of instability 2 to 6 weeks after injury, inversion and eversion stress x-rays should be obtained and compared to the noninjured side. These radiographs are assessed for talar tilt during stress. MRI imaging can also be obtained to assess for injury to the ligamentous complexes of the ankle.(A1)

Wight et al conducted a systematic review and reported that 88% of patients with closed pure ankle dislocations were treated without surgery.[1] Surgical treatments included deltoid ligament reconstruction or repair, screw or tightrope fixation of the tibiofibular syndesmosis, external fixation, and lateral ligament reconstruction or repair. Patients with open injuries were treated with surgical debridement in 95% of cases, with half of those patients undergoing acute ligamentous repair. (A1)

Ankle fracture-dislocations are often treated operatively as they result in unstable bimalleolar and trimalleolar fractures. After a concentric reduction, these injuries can be approached similarly to unstable ankle fractures that did not result in a dislocation. The main principles of surgical fixation are to obtain an anatomic reduction of the articular surface, restore fibular length, and use rigid fixation. 

The surgical approach is dependent on the nature of the fracture. Bimalleolar fractures are often approached with a 2-incision technique, with fixation of the fibula through a lateral approach and fixation of the medial malleolus with a medial approach. Trimalleolar fractures are also treated through a 2-incision approach with either a combined posterolateral and medial or posteromedial and lateral approach to gain access to the fibula, medial malleolus, and posterior malleolus.

Percutaneous techniques have been described for fixation of the medial malleolus; however, open approaches offer direct visualization of fracture reduction. The medial approach can be done with either a longitudinal incision or via the approach described by Colonna and Ralston in 1951.[20] This approach uses an incision beginning 4 inches above and 1 inch behind the medial malleolus, then curves anteriorly and distally to the midpoint of the malleolus, and then curves posteriorly and distally to the tip of the malleolus. Dissection is carried down to the bone and reflected subperiosteally, both anteriorly and posteriorly, while preserving the deltoid ligament. This allows access to a complete visualization of the fracture fragments to obtain anatomic reduction. The dissection can be taken posteriorly to access a posterior malleolar fragment if necessary. This is done by incising the tendon sheath of the posterior tibial and flexor digitorum tendons and reflecting the tendons anteriorly. The neurovascular bundle and flexor hallucis longus (FHL) tendon are retracted posteriorly, which gives access to the posterior malleolus.

Medial malleolus fixation involves anatomic reduction using a reduction clamp, followed by assessment of the reduction by direct visualization and fluoroscopic imaging. The mode of fixation of the medial malleolus depends on fracture orientation. Supination-external rotation, pronation-abduction, and pronation-external rotation type injuries often result in a transverse medial malleolar fracture.[8] These fractures are typically fixed with 1 or 2 screws placed from the tip of the medial malleolus and oriented perpendicular to the fracture line. Bicortical screw fixation offers greater construct stiffness than unicortical screws.[21] Supination-adduction injuries typically result in a vertically oriented fracture pattern. These fractures require a medial plate and screw construct placed in a buttress or anti-glide fashion to prevent proximal migration of the fracture fragment.[21] (B3)

The fibula can be approached via a straight lateral or posterolateral approach. The posterolateral approach allows access to both the fibula and the posterior malleolus if needed. The lateral incision is placed midway between the anterior and posterior borders of the fibula and starts distal to the tip of the fibula and extends proximally. The length of the incision is dependent on the location and pattern of the fracture. Dissection is taken down to the bone, and the fibula is exposed by sharp dissection.[20] The surgeon must be aware of the superficial peroneal nerve, which typically crosses from posterior to anterior across the fibula approximately 12 cm from its tip. The fixation strategy again depends on fracture orientation and pattern. Principles of fixation include the restoration of anatomic fibular length, anatomic reduction in simple fracture patterns, and rigid fixation. Fibular length is assessed on mortise-view x-rays intraoperatively and can be estimated by comparing the talocrural angle of the injured and noninjured extremities.[22] Simple oblique fracture patterns can be treated with lag screw fixation perpendicular to the fracture to provide compression across the fracture site. Lag screws are typically augmented with a laterally based plate in a neutralization fashion to provide rotational stability to the fracture. Transverse fractures are typically treated with compression-type plating, and comminuted fractures are treated via bridge-type plating. Compression plating relies on an anatomic reduction and compression across the fracture site. This provides little to no micromotion at the fracture site, allowing primary bone healing without callus. Bridge plating works by allowing micromotion between comminuted fracture fragments. This allows for secondary bone healing via initial callus formation and then remodeling.

There is no consensus on the treatment of posterior malleolar fractures. For most orthopedic surgeons, the decision to fix the posterior malleolus is dependent on the size of the fracture. Small avulsion fractures typically do not need fixation; however, large displaced fragments often do. Many authors advocate for fixation of the posterior malleolus if it involves more than 25% to 30% of the articular surface.[23] The posterior malleolus can be approached via a posterolateral approach or the previously mentioned posteromedial approach. The posterolateral approach uses an incision midway between the Achilles tendon and the posterior border of the fibula. The sural nerve is found on the lateral border of the Achilles tendon and must be identified and protected. Deep dissection is done between the FHL medially and the peroneal tendons laterally. Dissection of the FHL muscle belly off of the posterior surface of the tibia gives access to the posterior malleolus fragment. The posterior malleolus fracture is typically vertically oriented and can be treated with either bicortical screws perpendicular to the fracture or can be treated similarly to the vertical type medial malleolus fractures described previously, with a buttress or anti-glide type plate to prevent vertical migration of the fracture.[23](B2)

After the malleoli have been addressed, the last structure to evaluate is the tibiofibular syndesmosis. Precise diagnosis of syndesmosis injury intra-operatively is difficult, and surgical indications for fixation remain controversial. Syndesmosis injuries occur in 10% to 13% of all ankle fractures.[24] Surgeons typically evaluate the syndesmosis using intraoperative stress radiographs. Two common stress tests used are the external rotation stress test and the lateral stress test. The external rotation test is performed by first obtaining a mortise view, then applying dorsiflexion and external rotation stress to the ankle, followed by a repeat mortise view. If there is additional gapping of the syndesmosis or a widened medial clear space, the syndesmosis is considered unstable and warrants fixation. The lateral stress test is accomplished again with a mortise view, then using an instrument such as a bone hook or pointed reduction clamp to pull the fibula laterally. If there is additional gapping of the syndesmosis, it is considered unstable and warrants fixation. A study by Stoffel et al concluded that the lateral stress test was more reliable than the external rotation stress test for detecting syndesmotic injury.[25](A1)

Syndesmosis fixation has classically been accomplished by compressive reduction with either a reduction clamp or manual reduction by the surgeon, followed by fixation with 1 or 2 screws placed from the fibula into the tibia parallel with the tibiotalar joint. More recently, there has been enthusiasm for the use of a dynamic suture button instead of screws, with the thought that these devices prevent diastasis while allowing tibiofibular rotational motion. A recent randomized controlled trial found improved patient outcomes and less radiographic syndesmotic widening with suture button use; however, concerns remain about the increased cost of these devices.[24](A1)

Postoperatively, patients are placed in a non-circumferential splint and made non-weight-bearing with crutches for at least 6 weeks. Patients who are diabetic may be kept without weight-bearing for longer periods, depending on radiographic healing and the surgeon's postoperative protocol preferences.

Differential Diagnosis

An ankle dislocation or fracture-dislocation is evident on physical exam, and noting the position of the foot relative to the tibial crest and patella is central to making the correct diagnosis. A subtalar dislocation can occur independently or in conjunction with an ankle dislocation or fracture-dislocation. These injuries, in isolation, can be mistaken for an ankle dislocation on physical exam; however, plain films show a reduced tibiotalar joint space. Higher energy mechanisms can also result in total talus extrusion (tibiotalar and subtalar dislocations). This injury is also identified on plain radiographs and requires immediate orthopedic consultation.

Prognosis

For pure ankle dislocations, the overall prognosis is favorable. In a systematic review of pure ankle dislocations, Wight et al found that most patients were asymptomatic after appropriate treatment. Those who were symptomatic (primarily female) complained of stiffness or post-traumatic arthritis. Closed dislocations were associated with fewer symptoms than those with open dislocations. Prognostic factors that have been associated with worse outcomes include advanced age, presence of vascular injury, delay to reduction, and inferior tibiofibular ligament injury.[1] Late complications reported include stiffness, degenerative changes, joint instability, and capsular calcification.[6]

The prognosis for ankle fracture-dislocation is variable. Compared with non-dislocated ankle fractures, ankle fracture-dislocations have worse long-term outcomes. SER and PER ankle fracture-dislocations were found to have significantly poorer results on the Foot and Ankle Outcome Score as measured by increased pain and decreased activities of daily life.[26][27] A recent study by Pincus et al demonstrated a higher rate of ORIF revision for ankle fracture-dislocations compared with the non-dislocated group (OR, 1.82; CI, 1.26-2.6).[28] Evidence of post-traumatic osteoarthritis of the ankle (PTOA) has been reported in up to 63% of patients sustaining an ankle fracture-dislocation.[11] Factors contributing to this result include the type of fracture, the patient's sex, and the accuracy of reduction. In the earliest and largest prospective study of ankle fracture-dislocations (as described below), an "excellent" to "good" outcome was observed in 82% of patients at 2 to 6 years of follow-up.[29]

Complications

The outcome and complication rate after an ankle dislocation or fracture-dislocation are multifactorial. Complications most commonly include infection, malunion or nonunion, skin necrosis, and post-traumatic arthritis. Factors that can influence a patient’s outcome include the mechanism of injury, fracture type, open fractures, and medical comorbidities. Higher energy mechanisms are more likely to result in more severe fracture patterns and open fractures.

Open injuries carry a high rate of deep infection (8%) and skin necrosis (14%) after immediate fixation.[30] Surgical-site infection after fixation was shown by Thangarajah et al.[31] to be higher in patients who smoke and those with bimalleolar fractures; not all of these injuries were fracture-dislocations. Complications include malunion, wound healing issues, and deep infection. These are seen at a higher prevalence in diabetics with ankle fractures treated both operatively and non-operatively, with a rate as high as 42% in diabetic patients compared to a matched cohort of nondiabetic patients in a report by McCormack et al.[32] Lindsjo et al conducted the largest and earliest prospective study of 306 patients with ankle fracture-dislocations who underwent operative fixation and were followed for up to 6 years after surgery.[29] The author reported an infection rate of 1.8% and a post-traumatic arthritis (PTOA) rate of 14%; more recent studies have reported a PTOA rate of up to 63%.[11]