BACKGROUND: Recent literature has focused on the role of the posterior malleolar fracture on syndesmosis stability. The primary purpose of this study is to determine if fixation of the posterior malleolus in SER IV ankle fractures would decrease the need for syndesmotic screw fixation. METHODS: A retrospective chart review was performed on all adult patients with trimalleolar or trimalleolar equivalent ankle fractures treated by two attending surgeons (TVL, ML) between October of 2006 and April of 2011. Preoperative standard three-view ankle x-rays and CT scans of the ankle were evaluated to confirm the diagnosis of trimalleolar fractures and to classify the pattern in regards to the Lauge-Hansen. Operative notes and intraoperative fluoroscopic stress views were reviewed to evaluate ankle stability. Finally, postoperative radiographs were evaluated for fixation patterns. RESULTS: A total of 143 trimalleolar or trimalleolar equivalent ankle fractures were evaluated for the study. Of these, 97 patients (average age 44 [range, 19-85]) sustained fractures classified as SER IV (69%) type injuries. Seventy-four of the 97 patients (76%) with SER IV patients had sizable posterior malleolus fragment for fixation. Thirty-four received posterior malleolar fixation and 40 did not. Among the 34 SER IV with posterior malleolar fixation, only 7 (20.6%) required additional syndesmotic fixation while when the posterior malleolar fragment was not fixed, 27/40 (68%) required syndesmotic fixation (P=0.0002). 15/34 posterior malleolar fixation was performed with indirect reduction using an anterior to posterior screw. 19/34 was performed with direct reduction using posterior plate fixation. 7/15 (anterior-posterior screw fixation) still required syndesmotic stabilization (46.7%). 0/19 (plate fixation) required syndesmotic stabilization (P=0.0012). CONCLUSION: Fixation of the posterior malleolus fracture in SER IV ankle fractures could restore syndesmotic stability and, thus, lower the rate of trans-syndesmotic fixation. Subsequently, this would eliminate the need for transyndesmotic screw removal.