The Prognosis of the Posterior Malleolar Fracture in the Syndesmosis Injury

Category: Trauma; Ankle Introduction/Purpose: Syndesmosis injuries, often involving the posterior malleolus (PM), are common in rotational ankle fractures. Concomitant intra-articular involvement, along with deltoid ligament rupture and open reduction and internal fixation (ORIF) affects outcomes predisposing to postoperative complications. Our study aims to investigate the outcomes of posterior malleolar fractures with concomitant syndesmosis injuries and identify prognostic factors associated with these injuries. Methods: This retrospective study investigated posterior malleolar ankle fractures with syndesmotic injury in 71 patients between January 2004 and March 2021. Among these, there were 54 cases of trimalleolar fractures and 17 cases of trimalleolar equivalent fractures. After receiving IRB approval from a single Korean center institution, demographic data, revision surgeries, syndesmotic implant removal, deltoid ligament rupture, deltoid ligament repair, types of implants, and insurance status were evaluated by an expert surgeon affiliated with the institution. Weight-bearing plain radiographs were analyzed for various parameters including superior and medial clear space (MCS), tibiofibular overlap, tibiofibular clear space, implant height, fibular shortening, and synostosis. Radiographic parameters were recorded preoperatively, postoperatively, at 3-month follow-up, and final follow-up. CT scans were utilized to assess posterior malleolar fracture involvement and evaluated using the Haraguchi classification. The severity of ankle joint obliteration was determined. Fibular shortening and synostosis presence were assessed from follow-up radiographs. Results: All radiographic parameters showed significant improvement over time (p-=0.001). No significant differences were found between groups with and without deltoid ligament rupture, except for postoperative 3-month TFO, which showed a significantly higher value in group of the deltoid ligament rupture (p=0.001). Fixation of the posterior malleolar fracture was significantly associated with a preoperative MCS with optimal cut off value of 3.72 mm as absolute value and 84% as the percent divided by the superior clear space as in area under curve (p=0.001, AUC=0.717). Male sex was significantly associated with unexpected syndesmotic implant removal. Deltoid rupture was significantly associated with postoperative ankle osteoarthritis. Preoperative TFC and ORIF of the posterior malleolar fracture were negatively associated with postoperative ankle osteoarthritis. Conclusion: A preoperative medial clear space measurement of 3.72 mm or more in posterior malleolar fractures with syndesmotic injury may be beneficial in deciding the fixation approach for posterior malleolar fractures. Male gender is identified as a risk factor for unplanned removal of syndesmotic implants. Deltoid ligament rupture, preoperative tibiofibular clear space (TFC), and the need for posterior malleolar fixation may be regarded as risk factors for postoperative ankle osteoarthritis.