CASE 50 syndesmotic injury

A 43-year-old woman complains of right ankle pain and inability to bear weight after she slipped and fell while walking down her driveway. AP and lateral radiographs of the right ankle are shown in Figure 6–52A–C.

 

 

 

Figure 6–52 A–C

 

Which the following findings should raise one’s suspicion of an associated syndesmotic injury?

1. Tibiofibular clear space measuring greater than 6 mm in both the AP and mortise views

2. Tibiofibular overlap of greater than 1 mm in the AP view

3. A spiral fracture of the proximal third of the fibula

4. Dynamic fluoroscopic views that demonstrate decreasing degree of tibiofibular overlap with progressive internal rotation

Discussion

The correct answer is (C). A spiral fracture of the proximal fibula (Maisonneuve fracture) is associated with a syndesmotic injury. In both the AP and mortise views, the tibiofibular clear space should measure less than 6 mm. The tibiofibular overlap should be greater than 1 mm in the mortise view. In the absence of injury, both the tibiofibular overlap and medial clear space decrease normally with internal rotation.

The patient is indicated for open reduction and internal fixation. After fixation of the fibula and medial malleolus, a stress test is performed and the syndesmosis is

found to be unstable.

 

Which of the following statements is true regarding fixation of the syndesmosis?

1. Because of the morphology of the talus, the syndesmosis should be reduced with the ankle in dorsiflexion so as to not risk over tightening of the joint.

2. Cadaveric studies have demonstrated screws engaging four cortices to be stiffer compared to those engaging three cortices.

3. The trajectory of the screws should be oriented parallel to the tibiotalar joint in the coronal plane and parallel to the surface of the operating table with the leg in neutral rotation.

4. Syndesmotic screws should be inserted in a lag fashion to augment compression across the joint.

Discussion

The correct answer is (B). Cadaveric studies have demonstrated that engaging four cortices improves syndesmotic stability although it is unclear if this finding results in any difference in clinical outcome. Tornetta et al. demonstrated that maximal dorsiflexion during syndesmotic reduction is not necessary to avoid overtensioning of the syndesmosis. The trajectory of the syndesmotic screws should be 25 to 30 degrees obliquely from posterolateral to anteromedial to account for the posterior position of the fibula relative to the tibia in the axial plane. Syndesmotic screws should be fully threaded and not inserted in a lag fashion to avoid overtensioning.

Which of the following statements is FALSE regarding the fixation of medial malleolar fragments?

1. Non-comminuted fractures of the anterior colliculus larger than 1 × 1 cm can typically be fixed with a screw.

2. Screws should be inserted posterior to the anterior colliculus so as to diminish the likelihood of injuring the posterior tibial tendon.

3. Regarding the competence of the deltoid ligament, the size of the medial malleolar fracture has been shown to be the most important variable in determining stability.

4. Screws placed with the lag by method technique have been shown to be biomechanically superior to partially threaded screws placed with the lag by design technique.

Discussion

The correct answer is (B). In a cadaveric model, Femino et al. showed that screws inserted posterior to the anterior colliculus resulted in screw-posterior tibial tendon contact in all the specimens and frank tendon injury in 50% of the specimens. Tornetta demonstrated that the deltoid ligament is typically spared in supramalleolar fractures and incompetent in fractures of the anterior malleolus measuring less than 17 mm in the sagittal plane. Biomechanical analysis and prospective series have shown fully threaded screws using a lag by technique method to be biomechanically and clinically superior to partially threaded screws inserted in the lag by technique method for fixation of medial malleolar fragments.

 

Objectives: Did you learn...?

 

The radiographic findings suggestive of a syndesmotic injury?

 

 

Current concepts and understanding related to proper syndesmotic fixation? The proper technique for fixation of medial malleolar fracture fragment?