Abstract
BACKGROUND: The optimal treatment method for managing unstable Pauwels III femoral neck fractures remains undetermined. The aim of this study was to compare the biomechanical properties of two types of Femoral Neck Anti-rotation and Support System (FNAS) and a Femoral Neck System (FNS) in unstable Pauwels III femoral neck fractures. METHODS: Eighteen synthetic femoral models were implanted with one of three fixation devices: FNS, FNAS I, or FNAS II. An unstable Pauwels III (OTA/AO 31-B2.3) femoral neck fracture was simulated using a custom-made needle and osteotomy guide. Torsion and axial compression loading tests were conducted, and the torque, torsion angle, load to failure, displacement, and stiffness values were recorded. RESULTS: FNAS II exhibited significantly higher torsional stiffness (0.67 ± 0.10 Nm/°) compared to FNAS I (0.52 ± 0.07 Nm/°, P = 0.01) and FNS (0.54 ± 0.07 Nm/°, P = 0.005). FNS demonstrated significantly greater mean axial stiffness (239.24 ± 11.38 N/mm) than both FNAS I (179.33 ± 31.11 N/mm, P = 0.005) and FNAS II (190.07 ± 34.11 N/mm, P = 0.022). FNAS I (302.37 ± 33.88 N/mm, P = 0.001) and FNAS II (319.59 ± 50.10 N/mm, P < 0.001) showed significantly higher initial axial stiffness compared to FNS (197.08 ± 33.68 N/mm). Both FNAS I and II improved resistance to deforming forces at a load level before approximately 1000 N, which is sufficient to withstand the load from most daily life activities. No significant differences were observed in compression failure load among the groups. The failure patterns at the point of failure included the pull-out of the distal locking screw and reverse oblique intertrochanteric femur fracture for FNS, while for FNAS I and II, the failures were characterized by a cleft on the calcar femorale and a decrease in the load-displacement curve. CONCLUSIONS: In unstable Pauwels III femoral neck fractures, the FNAS II enhances stability and is easier to manage for reoperation. The results of the current study support the potential of FNAS II as an alternative option for treating unstable Pauwels III femoral neck fractures in young individuals.