Ratcheting Behavior of Intervertebral Discs Under Cyclic Compression: Experiment and Prediction

Area of Science:

• Biomechanics
• Spine Research
• Materials Science

Background:

• Intervertebral discs (IVDs) are crucial spinal components subjected to repetitive mechanical stress.
• Understanding the cumulative deformation, or ratcheting behavior, of IVDs is essential for diagnosing spinal defects and developing effective repair methods.

Purpose of the Study:

• To investigate the ratcheting behavior of lumbar intervertebral discs (IVDs) through experimental testing and theoretical modeling.
• To analyze the influence of varying stress parameters and disc segments on IVD ratcheting.

Main Methods:

• Lumbar spines from sheep were used, with IVDs prepared in situ for uniaxial cyclic compression testing.
• Tests were conducted using an Electronic Universal Fatigue Testing System, varying stress amplitude, stress rate, and examining different lumbar segments (L5-6, L6-7).

Main Results:

• IVD ratcheting strain showed distinct stages of rapid increase followed by stability.
• Increased stress variation and decreased stress rate led to greater ratcheting strain and strain rate.
• Higher stress rates and variations enhanced compression stiffness; the L6-7 segment demonstrated greater resistance to ratcheting compared to L5-6.

Conclusions:

• Intervertebral discs exhibit ratcheting behavior consistent with general mechanical principles.
• A developed constitutive equation effectively predicts IVD ratcheting strain evolution.
• Findings are significant for understanding IVD defects and guiding the development of regenerative therapies.