Impact of Age-Related Decline in Bone Mineral Density on Internal Fixation for Nondisplaced Femoral Neck Fractures: A Finite Element Analysis Using Virtual Simulation Models

Background As the global population ages, the incidence of femoral neck fractures (FNFs) is rising. While internal fixation is generally preferred for nondisplaced FNFs, clinical outcomes in elderly patients remain controversial due to high complication rates associated with osteoporosis. This study aimed to establish a novel finite element analysis (FEA)-based evaluation method using virtual models to isolate the independent biomechanical effect of age-related, region-specific decline in bone mineral density (BMD) on the stability of internal fixation for nondisplaced FNFs. Methods A 70° Pauwels angle nondisplaced FNF model was created using CT data from a 30-year-old woman and was fixed with a fixed angle device. Eight virtual femur models, simulating ages 30 to 100, were generated by adjusting regional volume-BMD (vBMD) based on established longitudinal aging data. Linear FEA was performed to simulate single-leg standing. Evaluation parameters included mean von Mises stress (VMS) on screws, the fracture risk index (FRI) of the surrounding cancellous bone, and the relative displacement of the fracture fragments. Results Increasing simulated model age was associated with progressive decrease in regional vBMD across all areas. This decline led to a concomitant increase in mean implant VMS and the FRI of the bone surrounding the screws, particularly in load-bearing regions and around screw threads. Between simulated ages 30 and 80, the FRI increased by 101% to 125% across the three screws, with the distal screw showing the greatest increase. Furthermore, fracture fragment displacement increased with advancing model age, indicating reduced construct stiffness. Conclusions Age-related reduction in vBMD alone significantly compromises the biomechanical stability of internal fixation in nondisplaced FNFs, even when fracture morphology and implant configuration are identical. These findings suggest that BMD assessment is essential for surgical planning; in cases of severe osteoporosis, surgeons may need to consider alternative strategies, such as arthroplasty, despite the absence of fracture displacement.