Periprosthetic fracture is one of the leading causes of knee implant failure. Risk factors are associated with a reduction in bone density or stock. The purpose of this study was to evaluate the reduction in bone stiffness with the risk of fracture using finite element (FE) analysis. The femur geometry was acquired from a three-dimensional reconstruction of magnetic resonance imaging (MRI) scans and the knee implant was digitized and imported into FE software. The anterior flange, screw region, and posterior supracondylar regions were crucial regions in determining the risk of fracture. The risk of fracture was accessed by compressive stress yielding criteria. With an increasing flexion angle and decreasing bone stiffness, the compressive stress of the trabecular bone approached its yielding point. This outcome also suggested that normal bone stiffness/stock at high flexion angles could also contribute to stress yielding, notwithstanding the small yielding volume. Yet, osteoporotic patients could have impaired bone reparability and accumulated bone yielding with a reduction of bone stiffness and sustainability. Physicians should be careful in their consideration of knee replacements for osteoporotic patients to reduce the possible risk of periprosthetic fracture.
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