Fractures of the talus are relatively uncommon (5%–7% of all foot fractures) but can result in significant morbidity. Subtle talus fractures can often go unrecognized on plain radiographs of the ankle. The posterior process is best evaluated on lateral views, whereas the lateral process should be evaluated on both lateral and AP views. The talar neck should be examined for subtle fractures. The talar dome may be the site of minor osteochondral injuries. Osteochondral injuries and fractures of the lateral and posterior processes without severe displacement often may be treated conservatively.
Fractures of the talar neck and body (which are the most common talar fractures with high energy trauma) are associated with arthritis, malunion/nonunion, and an increased risk of AVN, as the blood supply is predominantly retrograde from arteries that enter through the sinus tarsi into the talar neck. Mechanisms of injury are usually due to a dorsal force on the foot when it is plantar flexed (classically in a head on motor vehicle collision while pressing on the brake) or an axial load while the foot is inverted.
Talar neck fractures are classified by the Hawkins system.
The risk of AVN increases as the 4 grades increase:
- Type I is a simple nondisplaced fracture of the talar neck (AVN risk: 10%).
- Type II is a displaced talar neck fracture and subluxation or dislocation of the subtalar joint (AVN risk: 30%).
- Type III requires subluxation or dislocation of the subtalar and tibiotalar joint as well (AVN risk: 60%–90%).
- Type IV requires subluxation or dislocation of the talonavicular joint (AVN risk: nearly 100%).
Management is often operative. Hawkins I may be treated conservatively with immobilization and nonweightbearing. It is vital to recognize the fracture because, if it is goes unrecognized and is treated as a sprain, nonunion or AVN become more likely. Hawkins II may have a trial of conservative management if postreduction alignment is acceptable. However, up to 50% will require eventual open reduction, internal fixation (ORIF); therefore, in practice, most will be reduced operatively at the time of injury. Hawkins III and IV will always require ORIF.
Follow-up radiographs or MRI should be performed to assess for AVN in all fractures of the talar neck and body. MRI is sensitive for AVN as soon as 3 weeks after initial injury, although its detection may be hindered by an artifact generated by orthopedic fixation hardware.
Hawkins sign refers to subchondral osteopenia of the talar dome at 6 to 8 weeks after injury. This indicates bony resorption from disuse and implies a preserved vascular supply via the artery of the tarsal canal and the artery of the tarsal sinus.