Biomechanical and clinical evaluation of the posterosuperior screw in-out-in in the inverted triangular cannulated screws fixation of femoral neck fractures.

Purpose: The aim of this study is to evaluate the mechanical performance and clinical outcomes of the posterosuperior screw In-Out-In (IOI) and All-In in the inverted triangular cannulated screws fixation of femoral neck fractures. Methods: Comparison of the mechanical properties of three inverted triangular cannulated screws fixation configurations, IOI, All In-Low (AI-L), and All In-Narrow (AI-N), for femoral neck fractures with different Pauwels angles using finite element analysis. Biomechanical experiments involving torsion, anteroposterior compression, axial compression, and cyclic loading were conducted using ORTHObones artificial femurs. We retrospectively analyzed postoperative data from 91 patients with femoral neck fractures. Based on hip CT scans, patients were divided into the IOI group (32 cases) and the All-In group (59 cases), and the incidence of nonunion and avascular necrosis (AVN) of the femoral head were compared between the two groups. Results: Finite element and biomechanical experiments demonstrated that the IOI group exhibited superior performance compared to the AI-L and AI-N groups in terms of torsional, bending, shear, and fatigue resistance. The clinical follow-up revealed that the incidence of nonunion in the IOI and All-In groups was 9.38% and 8.47%, respectively, and the incidence of AVN was 15.63% and 15.25%, with no statistically significant differences between the groups ( Conclusion: Our study demonstrated that the IOI configuration exhibited superior mechanical performance compared to the All-In configuration, while not increasing the risk of nonunion or AVN, and thus may not justify repeated fluoroscopy to avoid this trajectory. However, given the retrospective nature and limited sample size, these conclusions require confirmation through larger prospective studies with longer follow-up.