Talus dislocations

                                     DR KS Dhillon

Anatomy of the talus

The talus is the second largest tarsal bone, and it is situated posteriorly in the hindfoot between the tibia and the calcaneus. Two-thirds of the talar surface is covered with articular cartilage and it has a tenuous blood supply. It has 5 articular surfaces and there are no muscles or tendons attached to it. The talus has 3 parts, namely the head, neck, and body. There are two processes on the talus (the lateral and posterior process).

The talus has seven articular surfaces.

Superiorly the talus through the talar dome forms the mortise joint of the ankle with the tibia, medial and lateral malleoli.

Inferoposteriorly there is a large oblique facet that is concave which articulates with the calcaneus to form the talocalcaneal joint.

Anteroinferiorly there are two facets that articulate with the calcaneus to form part of the talocalcaneonavicular joint. The talar head articulates anteriorly with the navicular to form the talonavicular joint.

Blood supply is provided by the posterior tibial artery into the medial side of body and sinus, anterior tibial artery/dorsalis pedis artery into head and neck, and peroneal artery into the lateral side of the body and sinus. 

Robust peritalar ligaments provide stability to the talus. These include:

• Anterior talofibular ligament
• Posterior talofibular ligament
• Talocalcaneal ligaments
• Tarsal sinus ligaments
• Cervical ligament
• Talocalcaneal interosseous ligament
• Deltoid ligament
• Anterior tibiotalar ligament
• Posterior superficial tibiotalar ligament
• Posterior deep tibiotalar ligament
• Dorsal talonavicular ligament

Talus dislocation

There several types of talar dislocation given its multiple articulations. These include tibiotalar dislocation, subtalar dislocation, total talar dislocation, and talonavicular dislocation.

1.Total talar dislocation.

Total talar dislocation is also known as extrusion of the talus or pan-talar dislocation. It involves a tri-articular dislocation of the talus at the tibiotalar, talonavicular, and subtalar joints.  Most injuries are compound.

It usually occurs due to a high‐energy impact to an inverted, plantar‐flexed foot resulting from a fall from height or from a motor vehicle accident.

Total dislocation of the talus is a rare injury and it accounts for only 0.06% of all dislocations and only 2% of talar injuries [1]. 

Limited blood supply and numerous articulations of the talus along with the fact that the injuries are frequently open, make the treatment of total talar dislocation difficult. Such injuries are often associated with complications such as avascular necrosis (AVN), infection, and osteoarthritis [2]. 

In patients with close dislocation, a close reduction is carried out under GA and if the reduction is stable a cast is applied for 6 weeks. If the reduction is not stable percutaneous pinning can be carried out to maintain the talus in its position. If a close reduction is not successful, open reduction is carried out.

In patients with open dislocation, wound irrigation, debridement, and temporary internal or external stabilization of the ankle is carried out.

If the talus is lost and cannot be found, tibiocalcaneal fusion and fibular graft is a surgical option.

Primary talectomy is not recommended. All attempts must be made to preserve the talus even in patients with total extrusion of the talus with significant contamination.

Besides the total dislocation of the talus, neurovascular, capsular, and ligamentous injuries and pressure necrosis are early concomitant injuries.  Late complications include AVN, infection, and post-traumatic degenerative arthritis. Post-traumatic osteoarthritis can occur after several years. 

Incidence of AVN after total dislocation of the talus varies between 24% [3] and 88% [4]. The incidence of posttraumatic osteoarthritis (PT) varies between 10% [3] and 44% [4].

Open talar dislocations are often complicated by soft‑tissue infection. The incidence of infection ranges from 11.5% to 38% [5,6]. Infection rate as high as 88.9% has been reported in the older days [7]. Over the years, infection rates have been brought down through improvement of staged procedures for wound care and soft‑tissue management and adapted antibiotherapy.

2.Subtalar Dislocation

Subtalar dislocations are also known as peritalar dislocations. Subtalar dislocation is a rare injury that accounts for 1%–2% of all dislocations. In subtalar dislocations, there is a separation of the talonavicular and talocalcaneal articulations. These dislocations are commonly caused by falls from height, motor vehicle crashes, and twisting leg injuries. The dislocations are divided into anterior, posterior, medial, and lateral types based on the direction in which the distal part of the foot moves in relation to the talus. The most common type is medial dislocation which results from an inversion injury. A medial dislocation occurs in about 71.5 % of the patients, lateral in 26.0%, posterior in 1.6%, and anterior in about 0.8% of the patients [8]. Most of the dislocations are close. An open dislocation occurs in about 22.5% of the patients [8]. Sometimes subtalar dislocations are associated with fractures of the navicular, calcaneus, and talus. Additional bony injury is seen in about 61.4% of the patients [8].

During the physical examination, the neurovascular status must be carefully assessed. Subtalar dislocations are treated with closed reduction under sedation. In about 14% of the patients close reduction is unsuccessful. If close reduction fails, immediate open reduction should be carried out. After reduction of the dislocation, X-rays and if necessary computed tomography scan should be performed to evaluate the alignment of the bones and evaluate the presence of fractures.

The overall outcome of treatment of subtalar dislocations is good in 52.3%, fair in 25.2%, and poor in 22.5% of the patients.

The most frequent late complications following subtalar dislocations include pain, decreased motion, subtalar instability, and degenerative joint disease [9,10]. Other complications that have been reported include avascular necrosis of the talus, RSD (reflex sympathetic dystrophy), and recurrent dislocation [11]. Some authors have reported no AVN following subtalar dislocations [11,12] while others have reported a low incidence of 4% to 6% [9,10]. In patients with severe open fracture-dislocations of the subtalar joint a high incidence of 33% has been reported [13].

About 80% of patients with subtalar dislocation show significant restriction of motion and about 30% show roentgenographic evidence of arthritis [14].

3.Talonavicular Dislocation

Isolated dislocation of the talonavicular joint is a rare injury. These injuries are caused by severe adduction or abduction force applied to the forefoot. 

A medially or laterally directed force applied to the foot causes dislocation of the talonavicular joint without dislocation of the subtalar joint. The calcaneum along with the remaining foot swivels on the intact interosseous talocalcaneal ligament. The dislocation can be medial or lateral depending on the direction of the force applied to the foot. Medial dislocation is more common than a lateral dislocation.

The dislocation is treated by close reduction and cast immobilization. If close reduction fails, an open reduction is carried out, and if the reduction is not stable, internal fixation with K-wires can be done. The leg is immobilized with a cast. 

4.Tibiotalar dislocation

The tibiotalar joint is formed by the tibia, fibula, and talus. Stability is provided by the strong medial (deltoid) and lateral ligaments.

Tibiotalar dislocation is also known as talocrural or ankle dislocation. Tibiotalar dislocations without associated fractures are very uncommon. More than 50% of these dislocations are posteromedial and 25% are pure posterior dislocations [15]. The majority of dislocations are open injuries. On rare occasions, the dislocation can be anterior/anterolateral, medial, or lateral.

The usual mechanism of injury is a fall on a fully plantarflexed foot. The fall forces the talus into a position posterior to the tibia. Other causes of dislocation include motor vehicle accidents and sporting injuries. 

Most cases of closed tibiotalar dislocations can be treated by close reduction under sedation and cast immobilization for 6 to 9 weeks [15].  Open injuries are treated with thorough wound lavage and débridement followed by reduction of the dislocation, stabilization with K-wires if necessary, repair of ligaments and capsule, and immobilization in a slab followed by casting.

The overall prognosis for tibiotalar dislocations is favorable. The majority of patients are asymptomatic following appropriate treatment [16]. Those who are symptomatic (primarily female) complain of ankle stiffness. Ankle instability is rare. Closed dislocations are associated with fewer symptoms as compared to open dislocations. Some of the prognostic factors that are associated with worse outcomes include advanced age, presence of vascular injury, delay in reduction, and inferior tibiofibular ligament injury [16].  Late complications reported include stiffness, degenerative changes, joint instability, and capsular calcification [17]. 

The incidence of posttraumatic osteoarthritis is about 25% and it often occurs in patients with open dislocations [18]. 

Conclusion

There several types of talar dislocation given its multiple articulations. These include tibiotalar dislocation, subtalar dislocation, total talar dislocation, and talonavicular dislocation. Most of the time these dislocations result from falls from a height. Other causes include motor vehicle accidents and sports injuries. 

The injuries can be open or close. Open dislocations are treated with wound debridement. The dislocation can be treated with close reduction. If close reduction fails open reduction can be carried out. If the reduction is stable the limb is immobilized with a cast for 6 to 8 weeks. If the reduction is not stable then the fragments can be stabilized with k-wires or external fixation.

The complications include loss of motion, instability, AVN, and posttraumatic arthritis. Generally, the clinical outcome is good. Open dislocations can result in poorer outcomes.

Reference

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