The significance of reduction of valgus-intercalated femoral neck fracture with valgus angle > 15°and the selection of internal fixation by finite element analysis

Currently, consensus is lacking on the necessity of internal fixation after reducing valgus-intercalated femoral neck fractures with abduction > 15°. This study employs finite element analysis to compare the biomechanical differences between the femoral neck dynamic cross nail system (FNS) and inverted cannulated screw (ICS), aiming to provide a foundation for clinical procedures. Human femur CT scan data were processed using MimICS21.0 and Geomagic 2021 software, imported into Solidworks2021 to create fracture models, based on Garden I abduction and Valgus-intercalated femoral neck fractures. The internal fixation model was divided into two groups: A-Anatomic reduction group; B-Valgus-intercalated femoral neck fracture group. ANSYS software facilitated meshing, material assignment, and data calculation for stress and displacement comparisons when ICS and FNS were applied in reduction or non-reduction scenarios. Without internal fixation, peak femur stress in both groups was 142.93 MPa and 183.62 MPa. Post FNS fixation, peak stress was 254.11 MPa and 424.81 MPa; peak stresses for the two FNS models were 141.26 MPa and 248.33 MPa. Maximum displacements for the two FNS groups were 1.91 mm and 1.26 mm, with peak fracture-end stress at 50.751 MPa and 124.47 MPa. After ICS fixation, femur peak stress was 204.76 MPa and 274.08 MPa; maximum displacements were 1.53 mm and 1.15 mm. ICS peak stress was 123.88 MPa and 174.61 MPa; maximum displacements were 1.17 mm and 1.09 mm, with peak fracture-end stress at 61.732 MPa and 104.02 MPa, respectively. Our finite element study indicates superior mechanical stability with internal fixation after reducing valgus-intercalated femoral neck fractures (> 15°) compared to in situ fixation. Additionally, ICS biomechanical properties are more suitable for this fracture type than FNS.