On the mechanical behaviour of intervertebral discs

Area of Science:

• Biomechanics
• Spinal Mechanics
• Computational Modeling

Background:

• Intervertebral disc (IVD) degeneration affects millions, leading to pain and mobility issues.
• Understanding IVD biomechanical response is crucial for developing effective treatments.
• Existing models often simplify the complex layered structure of the annulus fibrosus.

Purpose of the Study:

• To theoretically model the mechanical response of a lumbar intervertebral disc.
• To investigate the effects of compression, shear, bending, and axial rotation on disc properties.
• To analyze fibre strains under physiological loading conditions.

Main Methods:

• A theoretical disc model was developed.
• The annulus fibrosus was simulated using ten fibre layers with alternating inclinations.
• The nucleus pulposus and inter-fibre substance were modeled as incompressible fluids.
• End-plate bulging was incorporated into the model.
• Model geometry was optimized for lumbar disc representation.

Main Results:

• Disc stiffness significantly increased with higher axial loads.
• Substantial fibre strains, exceeding 10%, were observed during normal physiological motions.
• The model captured the complex response to various loading types (compression, shear, bending, axial rotation).

Conclusions:

• Axial loading plays a critical role in modulating lumbar disc stiffness.
• High fibre strains during physiological movements suggest potential mechanisms for disc injury.
• The theoretical model provides valuable insights into IVD biomechanics and injury risk.