Objective To compare the effectiveness between the posterolateral approach and the posterolateral combined posteromedial approaches in the treatment of Mason type 2B posterior malleolar fracture. Methods A retrospective analysis was performed on the clinical data of 79 patients with posterior ankle fracture who met the selection criteria between January 2015 and January 2022. There were 62 cases of Mason 2B Pilon subtype and 17 cases of avulsion subtype. Among Mason 2B Pilon subtype patients, 35 were treated with posterolateral approach (group A), 27 patients were treated with combined approach (group B). There was no significant difference in gender, age, injured side, cause of injury, time from injury to operation, preoperative hospital stay, preoperative visualanalogue scale (VAS) score, and intraoperative internal fixation between the two groups (P>0.05). All patients with Mason 2B avulsion subtype were treated by posterolateral approach, including 7 males and 10 females, aged from 25 to 68 years, with an average of 46.1 years. The operation time, intraoperative blood loss, postoperative hospital stay, and complications were recorded. The reduction quality was evaluated by Ovadia deals radiographic score, and the ankle function and pain were evaluated by VAS score, American Orthopaedic Foot and Ankle Society (AOFAS) score, and ankle range of motion. Results Mason 2B Pilon subtype: There was no significant difference in operation time, intraoperative blood loss, postoperative hospital stay, and follow-up time between the two groups (P>0.05). The radiological evaluation of Ovadia deals in group A was significantly worse than that in group B (P<0.05). The VAS score in the two groups significantly improved at each time point after operation, and the VAS score and AOFAS score further improved with the extension of time after operation, and the differences were significant (P<0.05). Except that the AOFAS score of group A was significantly lower than that of group B at last follow-up (P<0.05), there was no significant difference in VAS score and AOFAS score between the two groups at other time points (P>0.05). At last follow-up, the ankle range of motion in group A was significantly less than that in group B (P<0.05). There was no significant difference in the incidence of sural nerve injury, deep tissue infection, limitation of toe movement, and traumatic ankle arthritis between the two groups (P>0.05). Mason 2B avulsion subtype: The operation time was (119.47±20.61) minutes and the intraoperative blood loss was 50 (35, 55) mL. Seventeen patients were followed up 13-25 months, with an average of 18 months. The Ovadia deals score was excellent in 10 cases, good in 6 cases, and poor in 1 case at 1 week after operation, and the excellent and good rate was 94.1%. All fractures healed in 8-18 weeks with an average of 12.35 weeks. There were 1 case of sural nerve injury and 3 cases of traumatic ankle arthritis after operation. No deep tissue infection or limitation of toe movement occurred. The VAS score decreased significantly and AOFAS score increased significantly with time, and the differences were significant between different time points before and after operation (P<0.05). The ankle range of motion at last follow-up was (56.71±2.47)°. ConclusionCompared with the posterolateral approach, the combined approach is a better choice for the treatment of Mason 2B Pilon subtype. If the posteromedial bone block does not affect the reduction of the medial malleolus, the posterolateral approach can achieve good effectiveness for Mason 2B avulsion subtype.