Subject-specific finite element models can accurately predict strain levels in long bones

Area of Science:

• Orthopaedic Biomechanics
• Computational Mechanics
• Medical Imaging

Background:

• Accurate prediction of bone stress and fracture risk using patient-specific finite element models remains a challenge.
• Existing strain prediction accuracy in literature is variable and often unsatisfactory.
• Subject-specific finite element models require reliable material property assignments.

Purpose of the Study:

• To evaluate if selecting an appropriate density-elasticity relationship improves strain prediction accuracy in subject-specific finite element models.
• To assess the impact of different density-elasticity power relationships on numerical predictions.
• To determine if a single relationship is sufficient across the entire bone density range.

Main Methods:

• A combined numerical-experimental approach was used.
• Finite element models were generated from CT data of eight cadaver proximal femurs.
• Strain gauges measured experimental strains under six loading scenarios; these were compared to model predictions.
• Three literature-derived density-elasticity power relationships were implemented.

Main Results:

• The choice of density-elasticity relationship critically influences the accuracy of numerical predictions.
• One tested constitutive law demonstrated excellent agreement between predicted and measured strains (R(2)=0.91, RMSE < 10%).
• A single density-elasticity relationship applied across the full bone density range yielded sufficient accuracy for many applications.

Conclusions:

• Optimizing the density-elasticity relationship is crucial for accurate bone biomechanical modeling.
• The study validates a specific relationship for reliable strain prediction in orthopaedic biomechanics.
• The findings support the use of simplified, yet accurate, material property assignments in patient-specific bone models.