Foot and Ankle cases 20

A 26-year-old man sustained an injury to his right ankle when he was caught in an avalanche while snowboarding. He was unable to bear weight on the right foot and was taken to the emergency department for evaluation. His right ankle is noted to have mild to moderate edema with soft foot compartments, intact pulses, and intact light touch sensation. There are no fracture blisters or open wounds. Radiographs and CT of the right ankle are obtained in the emergency room (Figs. 5–42 and 5–43A and B).

 

 

 

Figure 5–42 Lateral radiograph of the ankle.

 

 

 

Figure 5–43 A: Axial CT. B: Sagittal CT. C: Coronal CT.

 

What is the best course of treatment?

1. Splinting the ankle in neutral position to prevent equinus contracture and plan for nonsurgical management

2. Urgent external fixation placement

3. Application of short-leg cast

4. Open treatment of the talus fracture in a timely manner

 

Discussion

The correct answer is (D). The imaging studies show a comminuted and displaced talar neck fracture. Hawkins described a classification system for talar neck fractures. Type I fractures are nondisplaced, type II fractures are displaced with subluxation or dislocation of the subtalar joint, and type III fractures are displaced with subluxation or dislocation of both the subtalar and tibiotalar joints. Canale and Kelly later added a fourth type that is a type III fracture with concomitant talonavicular dislocation (J Bone Joint Surgery, 1978). Operative treatment should

be considered in all displaced talar neck fractures, including Hawkins type I fractures.

Splinting the ankle in neutral dorsiflexion, while minimizing the chance of equinus contracture, may further displace the fracture. This fracture would likely not have significantly improved alignment with external fixation placement, and the current state of his soft tissue envelope does not preclude open reduction with internal fixation at the index procedure. Cast treatment would not be appropriate for this displaced fracture.

When considering the surgical approach for fixation of this fracture, what structures may be at risk during the dissection?

1. Superficial peroneal nerve

2. Branches of the dorsalis pedis artery

3. Branches of the posterior tibialis artery

4. All of the above

 

Discussion

The correct answer is (D). A displaced talar neck fracture with extensive comminution and extension to the talar head and the lateral process/body is best approached through a dual incision technique. The dual incision approach allows for mobilization of the fracture and verification of an adequate reduction. Often, the medial talus has extensive comminution. A dual incision technique allows for internal fixation along the medial and lateral aspects of the talus (Fig. 5–44), which often helps to prevent varus malunion. Medial dissection, particularly along the inferior talar neck should be done very carefully to avoid further injury to the deltoid branches and the artery of the tarsal canal, which supply the majority of the blood supply to the talar body. Extensive dissection along the dorsal talar neck may disrupt vascular branches from the dorsalis pedis artery that supply the talar head and neck. The superficial peroneal nerve may be at risk during the lateral approach to the talus and should be identified and protected. The artery of the sinus tarsi from the peroneal artery, which forms an anastomotic sling on the inferior surface of the talar neck, is also at risk with the lateral approach.

 

 

Figure 5–44 A: Intraoperative Canale view of the talus showing medial and lateral fixation. B: Intraoperative lateral view.

 

Based on the preoperative imaging studies, what is the patient’s approximate risk of developing avascular necrosis (AVN) of the talus?

1. Less than 15%

2. 15% to 50%

3. 50% to 75%

4. Greater than 75%

 

Discussion

The correct answer is (B). The Hawkins classification system is predictive of the risk of development of avascular necrosis of the talus. Based on the imaging studies, this fracture is classified as a Hawkins II fracture because of the mild subluxation of the subtalar joint seen best on the sagittal CT image. In Hawkins’ study on talar neck fractures, a 42% rate of AVN was seen in type II fractures. Subsequent studies, including Vallier et al. (J Bone Joint Surg, 2004) found that Hawkins type II fractures had an AVN rate of 39%.

 

Objectives: Did you learn...?

 

Describe the Hawkins classification for talar neck fractures?

 

Describe the importance of using a dual incision technique to obtain an anatomic reduction and avoid varus malunion?

 

Identify relevant vascular supply of the talus?