Can you describe the radiograph?

This is a lateral radiograph of the left ankle showing a displaced talar neck fracture. The subtalar joint is clearly dislocated, but the tibiotalar and talonavicular joints are congruent. This therefore represents a Hawkins type II fracture.

1.   How are these injuries classified, and what is the importance of the classification system?

These are described as follows, according to the Hawkins classification. The impor- tance is that the grade of injury can predict subsequent risk of developing AVN.

Type I – Undisplaced neck fracture: 10% risk

Type II – Displaced neck fracture with subluxation/dislocation of the subtalar joint: 30–60% risk

Type III – Displaced neck fracture with subluxation/dislocation of the subtalar and tibiotalar joints: 60–90% risk

Type IV – Displaced neck fracture with subluxation/dislocation of the subtalar, tibiotalar and talonavicular joints: Up to 100% risk

2.  What is the typical mechanism of injury?

The classical mechanism is an axial load to the dorsiflexed foot. This commonly occurs in road traffic accidents whereby the load from the pedal forces the talar neck against the anterior tibial plafond.

3.   How would you initially manage this injury?

This is a high-energy injury and should therefore be managed in the emergency department with concurrent assessment and resuscitation as per ATLS guidelines.

I would assess the neurovascular status of the limb and perform a circumferential examination of the skin to look for any signs of an open fracture. I would ensure the patient had satisfactory analgesia and place the patient in a below knee backslab prior to obtaining a CT scan.

4.  How would you definitively manage this fracture?

I would treat this displaced talar neck fracture with open reduction and internal fixation. I would approach this using an anterolateral incision and possibly an addi- tional anteromedial incision.

The anterolateral approach involves a longitudinal incision in the line of the fourth metatarsal, centred on the extensor digitorum brevis which directly overlies the subtalar joint and lateral talar neck. The superficial peroneal nerve is at risk here and full-thickness incisions without undermining are imperative. The extensor digitorum brevis is split and retracted, exposing the lateral aspect of the talar neck. Since the majority of fractures on the lateral side are simple compared with com- minution on the medial side, a ‘cortical key’ can be achieved to obtain reduction. If this is not possible, additional access and exposure can be obtained through an additional anteromedial approach.

The additional anteromedial approach involves an incision from the medial malleolus proximally to the base of the first metatarsal distally. The dissection is between the tibialis anterior and tibialis posterior, protecting the saphenous vein. This exposes the medial aspect of the neck and the body, although it may endanger the deltoid branch of the posterior tibial artery, which is often the only remaining supply to the body of the talus. This dual approach can be used when there is dif- ficulty with reduction.

I would debride the subtalar joint to remove any debris and confirm the frac- ture reduction using image intensification. Once reduced, I would fix the fracture temporarily with K-wires before applying definitive fixation with two cannulated, partially threaded, cancellous screws.

5.   What complications would you warn the patient about?

Starting with early complications, these would include wound dehiscence and infec- tion, particularly in open fractures. Compartment syndrome of the foot may com- plicate this high-energy injury.

Late complications include AVN, secondary OA, delayed union, mal-union and non-union.

Mal-union typically produces a varus deformity of the hindfoot due to compres- sion of the comminuted medial portion and subsequent loss of length of the medial column of the foot.

6.  What is the blood supply to the talus?

The talus has a complicated blood supply which is formed by three main arteries:

1.        Posteror tibial artery, leading to:

a.     Artery of the tarsal canal (main supply to the body)

b.     Deltoid branch (may be the only remaining supply in a displaced neck fracture)

2.        Dorsalis pedis artery (supplies the talar head and neck)

3.        Peroneal artery, leading to: Artery of the tarsal sinus