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Introduction/Purpose: Fractures of the posterior malleolus (PM) are present in 7-44% of all ankle fractures. Controversy exists referring to the optimal strategy for the fixation of these fractures. The anatomical reduction of the PM has been related to better functional outcomes and lower rates of posttraumatic osteoarthritis. The posterolateral (PL) approach has proven useful for obtaining an accurate reduction of the articular step-off and remotion of intraarticular fragments that may interfere with the reduction. Common reported complications are wound dehiscence, sural nerve injuries and persistent intraarticular step-off of the PM. There have been no previous reports on the literature regarding the learning curve (LC) of this approach. The aim of this study was to assess the LC of performing a PLA by orthopedic surgeons. Methods: A retrospective study was performed including patients with posterior malleolar fractures treated by eight orthopedic foot and ankle surgeons between 2012 and 2018 in a Level-I trauma center. Open reduction and internal fixation using a PL approach was used in all patients. Demographic data, fracture pattern and approach-related complications were noted. Anatomical reduction or persistent step-off and of the PM was assessed with postoperative CT-Scan. The LC-CUSUM (Learning Curve - Cumulative Sum) quantitative assessment was used to evaluate the learning curve in terms of approach-related complications and quality of reduction. Based on the acceptable failure rate was defined by less than 10% of approach-related complications and less than 15% of patients with postoperative step-off greater than 1 mm. Results: We included 167 patients with a mean age of 47 years old (R22 - 75). PM morphology was classified according to Haraguchi being I:52.1%, II:46.1% and III:1.8%. Mean size of the PM was 29.8% (R13 - 58). The overall approach-related complications incidence was 10.2 % being the most frequent: wound complications and sural nerve paresthesias. Persistent step-off >1 mm was present in 23 patients (13.8%) on CT-Scan. LC-CUSUM score peaked at the 31st case for significant reduction of approach-related complications. There was a decrease in the incidence of approach-related complications from 19.4% in the first 31 cases and 8,1% in cases 32nd-167th. There was a significant reduction of persistent step-off >1 mm with the LC-CUSUM score peaking after the 28th case. This manifests in a decrease from 21.4% incidence in the first 28 cases versus 12.2% in cases 28th-167th. Conclusion: The learning curve for fixation of PM fractures using a PL approach, as indicated by a cumulative sum quantitative assessment, corresponds to 31 cases for achieving success in terms of approach-related complications and 28 cases for an acceptable quality of reduction. These results are useful for novice trainees in this approach for defining a point of competence and assess the feasibility to achieve expertise in centers with lower caseloads of PM fractures. [ABSTRACT FROM AUTHOR]