Variability of intervertebral joint stiffness between specimens and spine levels

Area of Science:

• Biomechanics
• Spinal Engineering
• Computational Modeling

Background:

• Accurate characterization of passive mechanical properties of spinal joints is essential for musculoskeletal multibody models.
• Intervertebral joint stiffness is often literature-derived, neglecting inter-individual and spinal level variations.

Purpose of the Study:

• To evaluate an optimization method for personalizing intervertebral joint stiffness.
• To assess if this method captures expected variations between specimens and spinal levels.
• To determine the accuracy of using generic scaling ratios for spinal level dependency.

Main Methods:

• Created multibody spine models (T12 to sacrum) from CT data for six specimens.
• Developed models with uniform and level-dependent stiffnesses.
• Optimized initial stiffness values to minimize kinematic error under three loading conditions.

Main Results:

• Optimized stiffness varied significantly across specimens.
• Models with level-dependent stiffness were less accurate than those without.
• Personalized stiffness substantially reduced prediction errors.

Conclusions:

• Optimization successfully captured specimen-specific stiffness variations.
• Accounting for spinal level dependency is crucial for accurate kinematic predictions.
• Generic scaling ratios are insufficient for capturing spinal level dependency; personalized, load-specific stiffness is recommended.