Biomechanical study of internal fixation methods for undisplaced femoral neck fractures with osteoporosis based on the Pauwels angle: Fixed angle device versus three cannulated screws.

Background: This study compared the biomechanical properties of three cannulated screws (3-CSs) and a fixed angle device (FAD) for treating undisplaced femoral neck fracture (FNF) Pauwels types I and III, using finite element analysis (FEA) models created with nonlinear material properties; accurately reflecting the bone quality of osteoporotic patients.

Materials and methods: FEA involved three patients with a history of undisplaced FNF. Mesh generation was performed using the preoperative CT data. Two internal fixation models:3-CSs and FAD were created for Pauwels type I and III models with a fracture angle of 30° and 70°, respectively. Compression force and relative displacement of the fracture site, and von Mises stress (VMS) of the implants were evaluated. Data analysis involved paired t-test at p < 0.05 statistical level of significance.

Results: No significant difference was seen in the compression force between the two implants for Pauwels 30° and 70°models. There was no significant difference in the relative displacement and VMS between the two implants for Pauwels 30° model. However, both relative displacement and VMS were significantly higher in 3-CSs than in FAD for Pauwels 70° model.

Conclusion: Results indicate the need for FAD when treating Pawels Type III FNF with osteoporosis, since FAD fixation exhibited superior mechanical stability compared to 3-CSs. However, for the Pauwels Type I FNF, both fixation methods provided comparable stability. When considering the implant's simple and minimally invasive features, the clinical use of 3-CSs may be applicable. These findings highlight the importance of evaluating the Pauwels angle when determining the optimal fixation method for undisplaced FNF.