Objective To observe the clinical efficacy of internal fixation through a modified posterolateral approach in the treatment of lateral and posterior malleolar fractures.Methods From January 2015 to January 2018,25 patients with fracture involving the lateral and posterior malleolus were treated at Department of Orthopedics,The Second Affiliated Hospital to Wenzhou Medical University.They were 13 males and 12 females,aged from 18 to 70 years (mean,43.1 years).By the Lauge-Hansen classification for ankle injury,9 cases belonged to supination-supination type of degree Ⅲ,11 to supination-supination type of degree Ⅳ,and 5 to pronation-supination type of degree Ⅳ.By the Haraguchi classification,all the posterior malleolar fractures in this series belonged to type Ⅰ.Internal fixation through a modified posterolateral approach was performed for all the lateral and posterior malleolar fractures.Their operation time,fracture healing time and postoperative complications were observed.At the last follow-up,ankle joint function was assessed by the American Orthopedic Foot and Ankle Society (AOFAS) ankle-hindfoot scale.Results In the 25 patients,the operation time ranged from 50 to 100 min (mean,70 min).Of this group,21 patients were followed up for 12 to 18 months (mean,14 months).Bony union was achieved after 3 to 5 months after operation.Superficial wound infection was observed in 3 cases.No such complications occurred like postoperative adhesion,deep infection,contracture of flexor hallucis longus tendon,or loosening or breakage of implants.By the AOFAS ankle-hindfoot scale at the last follow-up,the ankle function was excellent in 13 cases,good in 6 and fair in 2.Conclusion The modified posterolateral approach is worth popularizing in clinic because it provides possibilities of fixating the lateral and posterior malleolar fractures by the same incision,not stripping the muscular origins of the flexor hallucis longus and reducing postoperative adhesion of the flexor hallucis longus.