Trimalleolar fractures, also known as posterior malleolar fractures, have been one of the most challenging aspects of ankle injury therapy for a very long time. This work purposed to measure influence 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 randomized prospective comparative study was 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. Two equal groups of patients were created: 15 patients in group A [posterior malleolus (less than 25% of articular surface) left untreated] and 15 patients in group B with posterior malleolar fragment (PMF) that was immediately fixed by screw or screw and plate. Results: Operative duration was considerably higher in group B than group A (p <0.001). Time to complete union and time to full ambulation were considerably higher in group B than A (p <0.001, =0.002 respectively). AOFAS score was substantially higher in group B than A (P-value =0.016). Conclusions: The results demonstrate longer operative time, higher AOFAS score in B than group A. In situations when the posterior malleolar fracture is fixed, transyndesmal screw fixation may not be necessary.