Category: Ankle; Trauma Introduction/Purpose: The controversy surrounding the indications for fixation of posterior malleolar fractures remains unresolved, particularly in cases of middle-sized fragments that make up between 10-25% of the joint surface. Although several studies have been conducted, the evidence to support the need for fixation of such fragments is limited, with a lack of level 1 evidence. This study aimed to assess patients with ankle fractures involving middle-sized posterior fragments and compare those who received posterior malleolus fixation to those who did not. The hypothesis was that fixation of middle-sized (10-25%) posterior malleolar fractures would result in superior functional and radiological outcomes in the short to mid-term follow-up. Methods: A prospective randomized-controlled study was conducted to assess the effects of posterior malleolus fixation in patients with acute rotational ankle fractures involving a middle-sized fragment. Eligible patients were included and randomly allocated into two groups, Group 1 receiving open reduction and internal fixation without posterior malleolus fixation, and Group 2 receiving the same procedure with posterior malleolus fixation, following informed consent. Prior to the study, a power analysis was conducted, indicating that a minimum of 16 patients in each group would be necessary to achieve 80% power and a 5% significance level. The randomization was conducted using an even/odd numbers technique, resulting in 20 patients in each group. Patient clinical and functional status was evaluated annually postoperatively, utilizing the VAS pain scale, AOFAS and SMFA scales. Radiological evaluations were conducted through direct radiographs, utilizing articular step-off evaluation and the Kellgren Lawrence osteoarthritis grading system. Results: The groups were comparable in terms of age, BMI, gender, and fracture type distribution. There were no significant differences in average follow-up times, posterior malleolus size, or height values. However, articular step-off greater than 1mm was more common in Group 1 (p=0.04). Despite slightly better functional outcomes in Group 2, there were no significant differences between the two groups in terms of VAS pain, AOFAS, or SMFA scores (functional, bothersome, and total). However, there was a trend towards significance in the SMFA Function score difference (p=0.07). Multivariate analysis showed that Haraguchi type 1 fractures had better functional outcomes in only the SMFA Bothersome parameter (p=0.03). Patients with articular step-off greater than 1 mm had significantly worse outcomes in all SMFA and AOFAS parameters (p < 0.05). Conclusion: In patients with closed rotational ankle fractures involving medium-sized (10-25%) posterior fragments, there was no significant improvement in functional or radiological outcomes with posterior fragment fixation at short to mid-term follow-up. Patients without posterior fixation were more likely to have articular step-off greater than 1 mm, which was associated with poorer functional outcomes. Despite similar outcomes in both groups, posterior fragment fixation may decrease the incidence of articular step-off and contribute to improved functional outcomes.