Type
Fahey and Murphy [11] classified this injury into five types based on the direction of the dislocation of the talar in relation to the tibia: anterior, posterior, medial, lateral, superior or any combination of these. According to Wight et al. [1], the most common type is posteromedial (46%), followed by medial (20%) and posterior (15%). Distinctly uncommon types are anterior, lateral, and anterolateral, as well as vertical dislocation in which the talus is displaced between the tibial and fibular. Furthermore, the open and closed injury occurrence rate is equal [1, 6]. When it comes to etiology, a review of the literature [4] indicated that road accidents (40%) are prevalent followed by sports trauma (35%), particularly motorcycle accidents (33%) and sports in which jumping is a fundamental component such as volleyball (13%) and basketball (8%) [4]. The diagnosis is made clinically according to the deviation orientation of the foot with respect to the tibia. Radiological examination is required to confirm the diagnosis and exclude the presence of fracture and other latent injury.
Mechanism
The rarity of ankle dislocation without fracture can be attributed to the complicated mechanism of the lesion. Plantarflexion of the ankle, axial loading and inversion violence contribute to posteromedial dislocations which are more common than any other types of dislocations because of the tendency to land with plantarflexion and inversion of the ankle in a fall from a height [4]. The body of the talus is trapezoidal shaped from front to back being wider anteriorly, and thinner posteriorly. The unstable position of the tibiotalar joint is plantarflexion because the narrow part of the talar body lies within the ankle mortise [11], which increases the flexibility of the ankle while decreases the stability of it. The tibiotalar joint have discrete stabilization structures medially and laterally regarding of the malleoli and the collateral ligamentous complexes while the anterior and posterior of the joint have no such structures to reinforce the thin capsule [4, 12], causing the tendency of dislocation on the anteroposterior direction without fracture. In addition, the fibular malleolus is approximately 1cm longer than the tibial one, thus eversion injury is less possible to occur with the bone intact. Furthermore, the deltoid ligament is much stronger than the lateral ligamentous complex, therefore being more protective. Our cases were all posteromedial dislocations but the rotary cultivator machine being the cause (patient #5, Fig. 3) has never been reported in the literature as far as we know.
Fernandes [13], who studied the mechanism of tibiotalar dislocation without fracture on cadaveric ankles, put forward that plantarflexion, axial loading and external rotation resulting in lateral dislocations while external rotation, dorsiflexion and axial loading contributing to superior dislocations. These two types could lead to tibiofibular syndesmotic disruption and therefore instability is expected [4]. Anterior dislocation is usually neglected in view of minimal deformity at the ankle joint [14, 15] of which the mechanism is plantarflexion, anterior force, axial loading [4, 16]. Rotatory dislocation is a typical type of low energy trauma with only a few cases been reported in the literature [2, 3, 15, 17, 18] since pure ankle dislocation is usually the result of high energy trauma such as traffic accident or fall from height [6]. The term rotatory refers to the spin motion of the talus in the frontal plane, which is still restricted in the ankle mortise without anteroposterior displacement [18].
The lesion needs adequate energy to make the talar been stuck by the structures around the mortise and cannot spontaneously return to its normal location when the force is eliminated. In most cases, the dislocation is open by the laceration of soft tissues on the opposite side of the dislocation, which make up the only covering of the malleoli [5]. In addition, neurovascular structures, tendons, and muscles are frequently involved in open dislocations. Aside from violent trauma, it has been postulated that predisposing factors that can contribute to the pathogenesis of this lesion are internal malleolus hypoplasia, lack of coverage of the talus, ligamentous laxity, weakness of the peroneal muscles, and previous ankle sprains [16, 19]. However, the literature lacked detail to prove these risk factors except for few cases [4, 10, 18]. We found no predisposing factors in our case series and it may attribute to the rarity of the injury.
Treatment Protocol
Regardless of whether the dislocation is open or closed, all the current authors agree of the necessity of an immediate reduction. Recovery of normal range of movement and the lower risk of complications depend on the swiftness of treatment [10]. Delayed repositioning is a negative prognostic factor [18] and repositioning prior to admission in the emergency department is recommended if the risks have been carefully assessed.
Anesthesia before reduction is recommended to permit complete relaxation of the muscles as well as eliminate patient’s pain and nervousness. The knee should be flexed to relax the pull of sural triceps on the calcaneus. Longitudinal traction is the first step with one hand hold the hindfoot and the other hold the forefoot. Pronation or supination of the foot is based on whether the shift is medial or lateral [4]. Dorsiflexion of the foot must follow longitudinal traction to allow the talus to return to its normal position in the case of posterior dislocation [4, 20]. To sum up, the reduction direction is just on the contrary of the dislocation direction and thorough knowledge of dislocation orientation and trauma mechanism is necessary for the maneuver.
The literature recommends six- to eight-week immobilization without bearing weight on the concerned extremity [4, 21, 22]. After that, a gradual increase of load and remobilization therapy can be started adapted to the level of pain and swelling, in which proprioception and pronation training playing an important role [23]. The average 6 weeks immobilization length recommended by the literature may be sufficient for ligaments healing and shorter immobilization times may minimize ankle stiffness and ROM loss. Controlled ankle motion (CAM) orthosis may shorten the immobilization period allowing patient to weight bearing walk as tolerated with crutches [24]. We also applied similar orthosis in some cases of ours.
Open injuries usually have a propensity for neurovascular deficits and infections, therefore appropriate treatment should never be postponed [6, 25]. Intra-venous antibiotics should be administrated promptly, and tetanus vaccination for immunization is recommended. Thorough debridement and abundant washout are principle. The application of drainage apparatus and vacuum-assisted closure therapy (VAC) depends on the concrete conditions of the contamination of the wound. External fixation is suitable for the primary stabilization of the affected joint [22, 23, 25, 26] especially in open cases with severe compound wound just as we showed in the 5 cases. However, there were two out of five patients immobilized with external fixators complaining of stiffness. And it is similar to the outcome of Wight [1] with 3/7 patients immobilized with external fixators developed stiffness while 23/134 (17.2%) patients immobilized with cast did. We postulated that external fixation increasing the probability of stiffness compared with short or long leg cast, although the small sample size of the series may make the outcome not be convincing enough or statistically significant. Otherwise, Sayit et al. [26] applied external fixator for primary stabilization and stated that rigid fixation of the ankle at a dorsiflexed position for 6 weeks shortens the disability period and assists in a faster recovery.
Whether To Repair The Ligaments?
Sufficient force in inversion usually results in tear of the anterolateral capsule attachments and the anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL), while eversion injury which is rare commonly results in tear of medial capsule attachments and the deltoid ligament [2, 4, 5, 7, 13, 20, 27]. Whether the torn ligaments should be repaired is still in controversy [1, 8, 12].
Most authors recommended that closed reduction followed by immobilization in a cast for six to eight weeks should be performed for closed tibiotalar dislocation if neurovascular involvement was excluded [5, 10, 28]. Toohey [8] reported a good long-term prognosis in closed pure tibiotalar dislocations treated with conservative treatment. Moehring [6] recommended nonoperative treatment for closed dislocation that is stable and have a congruent ankle mortise stating that instability is rare despite massive ligamentous disruption.
More controversy remains with regard to acute ligament repair for cases of open dislocation. Some authors recommended ligaments repair [5–7, 10, 29]. On the contrary, many authors had reported good function in their patients with open dislocation who were treated without ligamentous repair [3, 21, 30, 31]. Wilson et al. [20] believed that operative treatment was unnecessary. Tarantino [21] hold that ligaments repair is unnecessary since they are usually shredded and contused.
The deltoid ligaments
According to Garbuio et al. [5], it is not necessary to repair the medial collateral ligament. They stated that patients with open dislocations who were treated with only repair of the capsule had no difference in joint stability and long-term functional outcome with patients treated conservatively for a closed dislocation. Ucar et al. [31] reported favorable long-term results without ligament and even capsule being repaired in open pure ankle dislocations. Colville et al. [7] and Moehring [6] concur with the viewpoint that it is not necessary to repair the medial collateral ligament. But it is a remarkable fact that all the cases they reported were posteromedial dislocations. According to Moehring [6], the deltoid ligament is always injured but usually retains significant portion of its integrity in posteromedial dislocations, except in gross displacement. As is known, deltoid ligament is the primary stabilizer of the ankle, restricting talar anterolateral rotation in the ankle mortise. The disruption of deltoid ligament producing a marked decrease in the tibiotalar contact area, thus the severity of a medial injury will determine the reduction of ankle stability [32]. Kaneko et al. [29] and Demiralp et al. [33] reported that they performed medial capsule and deltoid ligament restoration in posterolateral cases and gained satisfactory follow-up outcome.
For ankle joint fracture combined with deltoid ligament injury, some authors suggested that repair of the deltoid ligament is unnecessary if the fibula was rigidly fixed and achieved an anatomical reconstitution [34, 35]. Similarly, we can speculate that the theory can be in common use with pure ankle dislocation since the fibula is intact. We concur with the viewpoint that it is not necessary to repair the medial collateral ligaments regarding none of the cases demonstrated obvious instability though only one patient got the torn ligaments repaired.
The lateral ligaments
Elisé [10] and Colville [7] reported a good long-term functional outcome with repairing of the lateral ligaments and capsule in open cases. Moehring [6] recommended repair of the torn lateral ligamentous complex and immobilization with short leg walking cast in the position of 90–110° of dorsiflexion in open posterior/posterior variant cases. Wroble et al. [3] stated that repair of the medial and lateral ligament complexes does not seem to have any effect on long-term outcome. They hold the view that closed reduction is almost invariably accomplished easily, and optimum treatment is immobilization in a short leg cast for 6 weeks with no weight bearing for the first 3 weeks. Previous randomized controlled trials have shown that, for complete lateral ankle ligament ruptures, 2–3 weeks of immobilization in a walking cast or orthosis [36] followed by range of motion exercises provided patients with similar outcomes to ligament repair [37, 38].
The inferior tibiofibular ligaments
In the majority of medial and posteromedial dislocations, the inferior tibiofibular ligaments are spared [6, 7]. However, in the case of superior and lateral pure ankle dislocation, the syndesmosis rupture and instability are expected [20]. Furthermore, regarding the mechanism of superior and lateral dislocations, the inferior tibiofibular syndesmosis and deltoid ligament are inevitably both involved. Burns et al. [39] showed that adding deltoid disruption to syndesmotic injury increased fibular diastasis by 0.7 mm which results a 39% decrease in tibiotalar contact area and a 42% increase in intraarticular pressure. Close [40] and Boden et al. [41] showed similar viewpoint that addition of medial injury to syndesmotic injury increased mortise width significantly. Sagi et al. stated that malreduction of a ruptured ankle syndesmosis is associated with poor clinical outcomes [42]. Therefore, ankle syndesmosis reduction and fixation in superior and lateral dislocations is necessary.
The literature review and recommendation
According to the systematic review of Wight [1], 46% of patients had nonoperative treatment; ligamentous repair was described in 48% (37/77) of open dislocations and 5% (4/76) of closed injuries, in which 27 (66%) repaired lateral ligaments, 10 (24%) medial ligaments and 24 (58%) anterior capsules. Ankle instability was rare (2.6%) (4/154) and not influenced by acute ligament repair.
An open dislocation permits exploration and repair of the ligamentous injuries. However, for open injuries, primary introduction of foreign materials does not seem to be advisable to begin with regarding the risks of infection. Studies have suggested that ankle ligaments repair should only be considered in cases of chronic ankle instability after failed functional rehabilitation [43] and that acute ligaments repair has similar outcomes to non-surgical management [10, 38]. Post-traumatic, clinically relevant instability of the upper ankle joint is rare [4, 21]. Finkemeier et al. [28] recommended non-operative treatment in both open and closed tibiotalar dislocations without fracture and late ligament repair if there is problematic instability. We concur with the viewpoint after reviewing of the literature and analyzing the outcome of cases we treated.
Prognosis
Although some late complications are reported such as stiffness, degenerative changes and joint instability [4, 10, 44], the result remains satisfactory in most cases over a long term, particularly in closed dislocations which are usually treated by nonoperative methods [8, 10, 12, 44]. The functional result for open dislocations is relatively worse and the complication rate is higher [1, 8]. The negative prognostic factors include advanced age, involvement of inferior tibiofibular ligament, presence of vascular injuries, delayed reduction, open dislocation, cutaneous necrosis, and infection [5, 8, 18].
According to Wight [1], Neurovascular compromise prior to reduction occurred in 30 cases (19%), while most of them were resolved after reduction. Particular attention must be paid to neurovascular complication such as dorsal pedal artery, superficial and deep peroneal nerve [4, 44] and neurovascular involvement can seriously compromise the foot’s vitality [31] and lead to paralysis or functional deficits. The literature reported some cases of amputation caused by vascular lesions [3, 6, 30]. De-Giorgio et al. [45] presented a case of a 55-year-old man died from anterior and posterior tibial artery tear following a pure anterolateral dislocation of the ankle. Elisé reported residual paresthesia in 25% of his 16 cases [10]. One chronic deep peroneal nerve paresthesia was reported by Rivera [4] as well as the author. Few infections occur in open cases with a rate of 8% [1, 6], and the only superficial infection in our cases was eliminated after appropriate treatment.
The most common complication in the literature is stiffness [1]. We postulate that it is associated with immobilization time and measurement, while rehabilitation exercise plays an important role to reduce its occurrence. Limited ankle range of motion is frequent long-term complication, which is found in 4 out of 8 of Wroble’s series [3] with a mean follow-up of 11.5 years postinjury. This often leads to a functionally not significant loss of motion with restriction of mobility in the tibiotalar joint between 0 and 10° [8, 12, 33] and our cases presented similar outcome. The literature reported 10% cases developed arthritis [1]. Narrowed joint space was found in five out of nine cases in Garbuio’s study [5] and Elisé S [10] reported four out of 16 cases, with two of which presented an overall narrowing of the joint over 50%. In our cases, patients developed more severe posttraumatic arthritis in whom the intraoperative exploration found tibiotalar facet chondral lesions. Lui [9] hold the view that the chondral lesion is the single most important contributing factor to the development of the posttraumatic ankle degeneration. It is reported that osteochondral lesions of the talus occur in up to 50% of acute ankle fractures and sprains [46] and more severe fracture pattern correlates with more severe chondral lesions [47]. We have reasons to believe that it is the same with ankle dislocations. However, the patients may have joint space narrowing but good outcomes [31].
Preventive measures such as proprioceptive reflex and pronator training seem advisable regarding the injury mechanism [23]. It is possible that high-top shoes and taping of the ankle joint might improve resistance to an inversion injury by limiting the degree of passive inversion and improving the muscle reaction time of the peroneus brevis muscle of unstable ankles [3, 48].