Objective:To revise the 2017 classification of irreducible intertrochanteric fractures and summarize reduction techniques of 2021 classification.Methods:A retrospective analysis was conducted of the 17 patients with irreducible intertrochanteric fracture who had been treated at Department of Orthopaedic Surgery, The Ninth People's Hospital of Shanghai, Shanghai Jiaotong University School of Medicine from January 2015 to December 2019. They were 7 males and 10 females, with an age of (73.2 ± 16.1) years. On the basis of 2017 classification, the irreducible intertrochanteric fractures were classified into 2 types in the present 2021 classification. Type Ⅰ were interlocking fractures which were further classified into 3 subtypes: type ⅠA were sagittal interlocking ones (7 cases), type ⅠB greater trochanter interlocking ones (one case) and type ⅠC lesser trochanter interlocking ones (one case). Type Ⅱ were separating fractures which were further classified into 4 subtypes: type ⅡA were sagittal separating ones (4 cases), type ⅡB coronal separating ones (one case), type ⅡC rotational separating ones(one case) and type ⅡD complete separating ones (2 cases). All patients were treated by closed reduction and intramedullary nailing with different reduction strategies corresponding to their fracture types (application of ejector rods, clamps or prying techniques, etc.). A total of 132 patients with reducible femoral intertrochanteric fracture who had been admitted during the same period were selected as the control group. The fracture reduction time, intraoperative blood loss and Harris hip score at the last follow-up were compared between the 2 groups.Results:The 2 groups were comparable because there was no significant difference in their preoperative general data ( P>0.05). Type ⅠA accounted for the highest proportion of irreducible intertrochanteric fractures [41.3% (7/17)], followed by type ⅡA [23.6% (4/17)]. The fracture reduction time [(44.6 ± 6.7) min] in the irreducible group was significantly longer than that in the control group [(39.2 ± 9.6) min] ( P<0.05). There was no significant difference in intraoperative blood loss or Harris hip score at the last follow-up between the 2 groups ( P>0.05). Conclusions:Compared with the "2017 classification" , the "2021 classification" is more concise and easy to remember, and can directly prompt the corresponding proper fracture reduction techniques. The patients with irreducible intertrochanteric fracture using proper reduction techniques can obtain functional recovery similar to that in the patients with reducible intertrochanteric fracture after reduction and fixation.