Defining an Anatomic and Radiographic Safe Zone for Posterior Malleolar Ankle Hardware Fixation

Abstract

Category: Ankle; Trauma Introduction/Purpose: There is a lack of consensus regarding optimal management of Posterior Malleolar Fractures (PMFs). Indirect reduction and fixation with posterior-anterior (PA) screw shows promise of avoiding the risks associated with direct reduction or indirect anterior to posterior (AP) approaches. Some authors have raised concerns about potential risk to nearby structures with PA technique, including hardware prominence into the syndesmosis. This study highlights the use of a posteromedial vertical syndesmotic line as a fluoroscopic landmark, helping surgeons avoid intra-syndesmotic placement. Methods: Indirect PA screw placement was completed on ten cadaveric specimens, followed by fluoroscopy in mortise and lateral views. Dissection was performed to assess screw placement relative to the posteromedial border of the syndesmosis. The posterior border of the syndesmosis was marked with a radiopaque wire. Repeat imaging was completed to validate the fluoroscopic posteromedial vertical syndesmotic line is representative of the posteromedial border of the tibial incisura. Results: On dissection, 9 of 10 cadavers had accurate screw placement with no penetration into the syndesmosis (Figure 1, bottom left & bottom right). Corresponding imaging showed the screw head to be medial to the marker on mortise view. For the specimen with penetration into the syndesmosis, imaging confirmed that the screw head was lateral to the marker on mortise views (Figure 1, top center & top right). The radiopaque marker correlated with the posteromedial vertical syndesmotic line for all specimens when comparing anatomic to radiographic findings. A radiographic safe zone is defined for the PA screw 12 mm medial to the vertical syndesmotic line to ensure no iatrogenic injury to the FHL tendon. Conclusion: This study demonstrated that the posterior incisura tibialis fluoroscopic landmark is unambiguous in localizing the posterior syndesmotic border (Figure 1, top left) and that screws medial to this line are safely out of the syndesmosis, while screws placed lateral are either in or at risk of intra-syndesmotic placement. A safe zone is defined for screw placement.