BACKGROUND:There is controversy regarding the need for marrow reaming in intertrochanteric fractures of the femur.Some believe that unreaming shortens operative time,reduces bleeding,and decreases intraoperative risk in elderly patients,but there is no basis for whether this move reduces the effectiveness of intramedullary nail support.Others believe that reaming allows for the selection of thicker diameter intramedullary nails for better mechanical support,but basic studies have shown that this approach carries risks such as fat embolism and destruction of bone(especially in elderly patients with osteoporosis). OBJECTIVE:To analyze the mechanical distribution characteristics of reamed and unreamed proximal femoral nail antirotation-Ⅱ in the treatment of type 31-A3 intertrochanteric fractures by finite element analysis. METHODS:A healthy volunteer was included,and CT scans of his femur were obtained in DICOM format,and the files were sequentially imported into Mimics,Geomagic Wrap,SolidWorks,Hypermesh,and Ansys software for processing.The A3.1,A3.2,and A3.3 intertrochanteric fracture models were obtained and assembled with 9 mm,11 mm diameter,and 170 mm length intramedullary nails,respectively,followed by assigning material properties,setting the interaction relationship of each contact surface and defining the load and boundary conditions,and then solved.The femoral stress distribution,internal fixation stress distribution,femoral displacement,and internal fixation displacement were observed in different models. RESULTS AND CONCLUSION:(1)The femoral stress was less than that of unreamed intramedullary nail fixation for each type of fracture,and the maximum stress value of the femur for A3.3 fracture was greater than that of A3.1 and A3.2.(2)The internal fixation stress was greater than that of unreamed intramedullary nail fixation for each type of fracture,and the maximum stress value of internal fixation for A3.3 fracture was greater than that of A3.1.(3)Reamed versus unreamed intramedullary nailing has less effect on femoral and internal fixation displacement and more effect on stress.(4)It is indicated that the use of reamed intramedullary nail fixation results in a reduction in femoral stress,an increase in the stress borne by the internal fixation as a whole,and a reduction in the stress borne by the distal locking nail.The use of reamed intramedullary nail fixation may provide better treatment results compared to unreamed intramedullary nail fixation.