Biomechanical evaluation of implant techniques for ipsilateral femoral neck and shaft fractures: A finite element analysis

Purpose No consensus has been reached regarding the treatment of ipsilateral femoral neck fractures and femoral shaft fractures (FNF + FSF). This study discusses the stability and differences between multiple single- and dual-implant strategies in the treatment of FNF + FSF and aims to provide a theoretical reference for clinical applications. Methods Based on multi-sample finite element analysis, models of basicervical FNF (bFNFs Pauwels III) combined with three different FSFs (proximal (PFSF), middle (MFSF), and distal (DFSF)) were developed. Five implant strategies were established: (A) reconstructive nail (RN), (B) proximal femoral nail antirotation II (PFNA-II), (C) three cannulated compression screws + retrograde intramedullary nail (3CCS + RIN), (D) dynamic hip screw + antirotation screw (DHS + AS) + RIN, and (E) femoral neck system (FNS) + RIN. The biomechanical characteristic of FNF + FSF treated with five strategies were statistically analyzed. Results In most cases, there was no significant difference between the single- and dual-implant groups in the FSF gait cycle (at 0 degrees hip joint pressure load or with FNF + MFSF). In other cases, the dual-implant group was predominant. Maximum mean stress of neck-screw: A (235.1 MPa) > B (194.1 MPa) > D (191.5 MPa) > E (181.9 MPa) > C (153.9 MPa) at 30 degrees hip joint loading; A (137.9 MPa) > E (126.3 MPa) > B (105.5 MPa) > D (104.1 MPa) > C (89.30 MPa) at 0 degrees; A (306.3 MPa) > B (261.6 MPa) > D (259.5 MPa) > E (246.2 MPa) > C (217.2 MPa) at -30 degrees. Meanwhile, group C had the lowest fracture interface stress and relative displacement of bFNFs. Conclusion Dual-implant strategy for combined fixation, which can effectively strengthen the integral structural stiffness of the femur, is recommended for FNF + FSF. 3CSS and DHS + AS in the dual-implant strategies have better regional stability of bFNFs.