A microstructure-based model for a full lamellar-interlamellar displacement and shear strain mapping inside human...

Area of Science:

• Biomechanics
• Biomaterials Science
• Computational Biology

Background:

• The annulus fibrosus interlamellar zones are recently recognized for their critical role in intervertebral disc (IVD) mechanics.
• These zones influence transversal and volumetric responses, impacting the disc's 3D behavior.
• They are implicated as initiation sites for annulus fibrosus tears and disc delamination, a precursor to disc herniation.

Purpose of the Study:

• To incorporate the interlamellar zones into a complete human lumbar IVD model for the first time.
• To enable accurate visualization and replication of lamellar-interlamellar interactions.
• To identify critical interlamellar zones associated with disc failure modes.

Main Methods:

• Development and implementation of a fully 3D chemo-viscoelastic constitutive model into a finite element code.
• Inclusion of the physical, mechanical, and chemical contributions of interlamellar zones.
• Modeling of chemical-induced volumetric response using experimentally-based fluid kinetics for both lamellae and interlamellar zones.

Main Results:

• Computational simulations of simple and complex physiological movements were performed.
• Numerical analysis provided insights into displacement and shear strain fields within the disc core and interlamellar zones.
• Observed numerical results were compared with literature-based MRI experiments.

Conclusions:

• The developed model accurately captures lamellar-interlamellar-nucleus interactions within the IVD.
• Critical interlamellar regions with high delamination potential were identified.
• These critical spots were analyzed and correlated with local kinetics and microstructure, providing insights into disc failure mechanisms.