Does FNS outperform CCS in Pauwel's type III fracture fixation: a combined experimental and numerical study.

Open reduction and internal fixation (ORIF) is the gold standard for fixing femoral neck fractures in young patients. Traditionally, Cannulated Cancellous Screws (CCS) are used in such cases, while the newer Femoral Neck System (FNS) offers dynamic compression with minimal implant footprint. The current study compares the biomechanical performances of CCS and FNS implants for Pauwels type III fracture fixation through a combined FE and experimental evaluation using composite femurs. The material property of cortical bone samples was first characterized using three-point bend tests and nano-indentation. The average Young’s modulus obtained from three-point bend tests was 6.76 ± 1.20 GPa, and from the nano-indentation tests was 6.29 ± 1.46 GPa. Under a compressive load of 800 N, the maximum observed vertical displacements in the intact bone, the bones fixed with CCS, and FNS were approximately 0.94 mm, 1.26 mm, and 2.00 mm, respectively. The FE-predicted values were in close agreement with the experimental values (R ≈ 0.99, p < 0.01). Under physiological loading of normal walking, the FE-predicted maximum von Mises stress in FNS (535 MPa) was higher than CCS (344 MPa). In the CCS fixation, the highest stress was observed near the fracture plane of the bone, whereas for the FNS fixation, the maximum stress was located in the cortical screw adjacent to the sideplate. The results from the current study have shown that the new implant system, FNS, does not outperform CCS fixation from a biomechanical perspective.