Review Question - QID 211297

The patient has sustained a Bosworth fracture-dislocation, which is a fixed dislocation of the fractured fibula behind the posterolateral tibial ridge. These fractures are generally irreducible via a closed means and require open reduction.

The initial radiographs in this vignette reveal posterior subluxation of the talus and fibula without significant coronal plane deformity. This deformity should raise the suspicion of a Bosworth fracture-dislocation, especially if closed reduction is unsuccessful. Bosworth fracture-dislocations can often be associated with posterior malleolar fractures, specifically of the posterolateral rim of the distal tibia. These injuries often fail closed reduction, given the engagement of the fibula behind the posterolateral tibial ridge, and frequently require open reduction. In this situation, the most effective method to reduce the fracture is through a posterolateral approach. This is the same approach that can then be utilized for the fixation of the posterolateral fragment and fibula.

Delasotta et al. discussed a case presentation of a 24-year-old male with a Bosworth fracture-dislocation in which the anterior compartment musculature was interposed within the fracture site, impairing both closed and eventual open reduction of the injury. The authors go on to discuss how 3D CT reconstruction of the bone and soft tissues can aid in both the diagnosis and preoperative planning of such injuries. They also note that these injuries should be admitted for compartment and neurovascular checks and undergo urgent surgical treatment.

Gardner et al. performed a cadaveric study directly comparing fixation of posterior malleolar fractures to syndesmotic stabilization in a simulated stage IV pronation-external rotation injury. Compared with the intact specimens, the authors found that fixation of the posterior malleolus restored 70% of the native stiffness, but syndesmosis stabilization only restored 40%. The authors concluded that given the likely integrity of the posterior inferior tibiofibular ligament in the setting of posterior malleolar fractures, anatomic reduction and fixation may be more appropriate than syndesmotic stabilization and better suited to restore stability.

Switaj et al. retrospectively evaluated the incidence of posterior malleolar fractures and posterior pilon variants in a 270 patients with operatively treated ankle fractures. The authors noted a relative frequency of posterior malleolar fractures of 50% and that of the posterior pilon variants of 20% within the entire cohort. While they found no significant difference in frequency of posterior malleolar or posterior pilon variants with regard to either AO/OTA or Lauge-Hansen classification, patients with posterior pilon variants were significantly older.

Figure A and B show the AP and lateral views of an ankle revealing a lateral malleolar fracture with tibiotalar subluxation and posterior dislocation of the fibula with respect to the posterolateral ridge of the tibia, consistent with a Bosworth fracture-dislocation.

Incorrect answers:
Answer 1: While a delay in treatment of ankle fracture-dislocations can lead to challenges with close reduction, a delay of one day is not excessive and the primary reason for failure of closed reduction is the incarceration of the fractured fibula behind the posterolateral ridge of the distal tibia.
Answer 2: The deltoid ligament may become entrapped in the medial clear space leading to persistent medial clear space widening, however this generally leads to only mild medial clear space widening and would not explain the significant displacement.
Answer 4: FHL tendon entrapment has been described as a block to reduction with lateral subtalar dislocation. However the primary reason for failure of closed reduction in the setting of a Bosworth fracture-dislocation is the incarceration of the fractured fibula behind the posterolateral ridge of the distal tibia.
Answer 5: Conversely, the EDB has been described as a block to reduction with medial subtalar dislocation, but not in the setting of a Bosworth fracture-dislocation.