Bone remodelling around internal fracture fixations used for treating femoral neck fractures: A finite element analysis

Femoral neck fractures necessitate effective fracture fixation techniques to ensure optimal outcomes. The study evaluates the bone remodelling around Dynamic Hip Screw with anti-rotational screw (DHS + AR) and Femoral Neck System (FNS) used for treating femoral neck fractures of Pauwels types I, II and III. Femur models were developed using CT imaging data. Fractures were modelled assuming smooth fracture surfaces. Isotropic heterogeneous CT-grey value-based bone material properties were employed in the bone model, and Ti-alloy was incorporated as implant material. Bone remodelling algorithm based on strain energy density was employed to predict the implants' effects under two loading conditions: normal walking and stair climbing. The density change (Δρ) was iteratively updated until convergence occurred (Δρ < 0.005 g/cm³ between two consecutive iterations). The investigation compared post-operative (PO) conditions with equilibrium (AE) states. Results revealed that strain shielding was approximately 27% lower in FNS-implanted models than DHS + AR models, indicating better biomechanical performance under adopted modelling assumptions. From PO to AE, axial deformation and rotational stability of the femoral head were reduced more in FNS models, with reductions of up to 13.57% and 83%, respectively. Micromotion was (below 100 μm) in all models except for FNS in Pauwels III fractures under PO conditions. However, it was reduced below 100 μm at AE. Lower bone loss was observed in FNS-implanted models while DHS + AR implanted models exhibited higher resorption. These findings suggest that FNS implants are predicted to provide better stability and favourable bone remodelling outcomes compared to DHS + AR screws.