Background: Trimalleolar fractures are often referred to as posterior malleolar fractures and have been the subject of continuing interest for a long time as one of the most controversial issues of the treatment of ankle injuries. The aim of this work was to evaluate the effect of posterior malleolus fractures direct reduction and internal fixation on syndesmotic injuries reduction, compared to the direct syndesmotic fixation in trimalleolar ankle fractures, on the functional and short radiological outcomes. Methods: This was a prospective randomized comparative study on the effect of posterior malleolus fractures reduction and internal fixation on syndesmotic injuries reduction, compared to the direct syndesmotic fixation in trimalleolar ankle fractures, on the functional and short radiological outcomes. Patients were divided into two equal groups: Group A: 15 patients with Posterior malleolar fracture left with no direct reduction and internal fixation and group B: 15 patients with posterior malleolar fragment that was fixed directly by screw or plate and screw. 1 case was excluded from group due to open syndesmosis during cotton test intraoperatively during fixing of posterior malleolus, so the patient needed trans syndesmotic screw. Results: Operative duration was significantly lower in group A than group B (p <0.001). Regarding the potential complications of procedures in groups A and B, infection occurred in only 1 (6.67%) patient in group B and didn't occur in group A, and mechanical irritation occurred in only 1 (6.67%) patient in group A and didn't occur in group B.