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Talar fractures and dislocations

Description

Talar fractures and dislocations are relatively uncommon orthopaedic injuries resulting from high energy impacts such as severe motor vehicle accidents or falls from significant height. Their importance lies in the fact that the talus is integral to weight bearing in humans and the propensity for complications, such as avascular necrosis of the talus body.

Structure and function

The talus is an architecturally complex structure, whose shape allows body weight to be distributed from the plantar surface of the foot to the leg. Anatomically, the talus is composed of three region:

  1. Body - consists of a dome (articulates superiorly with the end of the tibia, the tibial plafond), a central portion, posterior process (under which the flexor hallicus longus tendon passed) and lateral process. The body has relatively poor blood supply; this blood supply runs distal to proximal and thus is at risk with any fracture displacement.
  2. Neck – most commonly fractured zone. This area has the main blood supply to the talar body, thus fracture displacement here at the talar neck is particularly risky for the development of avascular necrosis of the talar body.
  3. Head – articulates with navicular providing abduction and adduction movements at the talonavicular joint.

Epidemiology

Talar fractures are rare injuries, representing 0.1 – 0.85% of all fractures (Fortin & Balazsy, 2001). Significant force of impact is required for fracture formation. Their significance lies in the potential for morbidity.

Clinical presentation

Fractures of the talar neck result from extreme dorsiflexion of the ankle whereby the neck of the talus is pushed violently against the anterior edge of the tibia.
More severe force may result in fracture dislocations.
Fractures of the body are usually the result of a compression injury such as fall from significant height.
The patient presents with a history suggesting high--energy trauma and a painful and swollen foot. Displaced fractures may present with obvious deformity or skin tenting (a dangerous sign).
Talar neck fractures are usually classified according to the Hawkins (1970) classification system, which allows for treatment options and prognostic value (risk of AVN).
This is a controversial system because lack of treatment distinction between Types II-IV. Students are advised to concentrate especially on the distinction between displaced and non-displacedt.

Hawkins Type

Description

Risk of AVN (%)

Treatment

Type I

Nondisplaced

0-15

No reduction needed

Type II

Displaced with subluxation or dislocation of subtalar joint

20-50

Controversial (Closed Reduction vs Open reduction and internal fixation )

Type III

Displaced with dislocation of body from ankle mortise

20-100

Open reduction and internal fixation

Type IV

Displaced with subluxation or dislocation of the talonavicular joint

-

Open reduction and internal fixation


Fracture of the talar head, body and lateral and posterior processes are uncommon. It would be help simply to recall a key feature of each:

  • Fracture of the talar head: usually involves talonavicular joint.
  • Fracture of talar body: often has displacement best visualised using CT imaging.
  • Fracture of lateral and posterior processes: Usually associated with the same mechanism of injury producing ankle ligament strains (and thus an "ankle sprain" with a severe presentation should suggest investigation for this injury).


Red flags

Because of the risk of AVN, talar fractures must be scrutinized closely; that is, the injury itself is a "red flag". Beyond that, tenting of the skin is a particularly worrisome sign, as it may lead to skin necrosis.

Differential diagnosis

The main differential diagnoses are not rival diagnoses but concomitant ones: that is, because severe impact is required for a talar injury, other foot and ankle injuries may be produced by the same mechanism. Specifically, fractures of the calcaneus and distal tibia and subtalar or total dislocation of the talus should be excluded. Also, as noted, an "ankle sprain" may really be a lateral process fracture.

Objective evidence

Talus fractures can be missed on foot xrays series (and are especially at risk for being missed if the films are dedicated ankle xrays that do not (or barely) include the talus).
The standard imaging regimen includes anteroposterior, lateral and oblique x-rays. The Canale view provides the best view of talar arch.
CT imaging allows for better definition of the fracture and associated soft tissue injuries.
MRI is particularly useful in the diagnosis of osteochondral fractures of the talus which usually occur on the lateral part of the dome of the talus.


AP view. Talar body fracture, sagitally orientated. There is also disruption of the tibiotalar and subtalar joints.
AP view. Lateral process fracture. LP= Lateral Process. LM= Lateral Malleolus.
 

On follow up xrays, a radiolucent line may be seen in the subchondral area. This is a good thing! The line results from bone reabsorption and thus, for this line to be seen, the bone must have a retained its blood supply. This line is called "Hawkins sign". It suggests avascular necrosis likely will not occur.

Risk factors and prevention

Talar fractures and dislocations are the result of high-energy trauma. There is anecdotal evidence that snow boarding may be a risk

Treatment options

Swelling is a major problem in talar fractures and dislocations – it causes pain and makes clinical examination difficulty. Consequently, swelling should be addressed with realignment, splinting and elevation of the foot (Solomon, Warwick, & Nayagam, 2010). Ice packs and intermittent foot compression can be considered.
Once fracture pattern is identified, definitive treatment should begin.
Nondisplaced fractures are treated with immobilization and initial non weight bearing. Progressive weight bearing and therapy is begun.
Displaced fractures of the neck require reduction. If skin tenting, reduction acquires more urgency due to risk of skin necrosis. If there is only subluxation (Type II) closed manipulation under general anaesthesia can be attempted first. If closed reduction fails, open reduction and internal fixation is required. For fractures with dislocation of the joint, open reduction and internal fixation is needed.
Displaced Fractures of the talar body, head and processes also require accurate open reduction and internal fixation . Prognosis is poor with considerable incidence of malunion, joint incongruity, avascular necrosis and secondary osteoarthritis. In the case of head and processes fractures (but not of the body) excision of fragments that are small and highly comminuted may be preferable.

Outcomes

Assuming that there are no other injuries, and rapid and appropriate treatment, the expected out for non--displaced fractures is a return to normal function in 12 weeks.
The other fractures do not do as well.
Talar neck fractures with displacement are associated with high complication rates. Elgafy et al (2000) retrospectively reviewed 58 talus fractures followed for a period of 30 months. In their study, 53.3% developed subtalar arthritis, 25% had ankle arthritis and 16.6% developed AVN (Elgafy, Ebraheim, Tile, Stephen, & Kase, 2000). The incidence of AVN was much more common in displaced fractures.
Intraarticular fractures are more likely to lead to post--traumatic osteoarthritis.


Miscellany

The talus is covered with articular cartilage more than any other bone in the foot. That makes it difficult for blood supply to enter. Further it has a retrograde blood supply, that the artery feeding the proximal end enters the bone at the distal end. Together, these make the blood supply more tenuous and AVN after fracture more likely.
A fleck of bone seen posterior to the talus on lateral xrays, the os trigonum, may appear like a fracture fragment; it is not.

Key terms and competencies

Talus; Talar neck fractures; Hawkins; Open reduction and internal fixation
Recognize displacement of talar fractures


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