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Increasing Gradients of Compressive Stress Can Lead to Annular Delamination, Collapse, and IVD Degeneration

delamination, annulus

A ISSLS Prize-winning study 1 examined how increasing gradients of compressive stress within the intervertebral disc (IVD) contributed to the progress of dis degeneration. The research findings suggest that an increased grade of disc degeneration created decreased nucleus pressure and compressive annulus stress, but anterior annular stress gradients increased by approximately 75 percent, and by 108 percent in the posterior annulus—findings that are clinically significant.

The neural arch may provide a stress-shield for the degenerating disc during mechanical loading, but delamination and collapse of the annulus are most likely caused not by loading, but by increasing gradients of compressive stress, leading to advanced disc degeneration, despite the stress-shield.

The Study

Using 191 motion segments from 42 cadavers of varied ages, researchers measured the intradiscal stresses under 1 kN of compression. A pressure transducer was pulled along the midsagittal diameter of the disc to measure the intradiscal stresses. Stress gradients in the annulus were quantified using a formula that averaged the rate of increase in compressive stress between the area of maximum stress in the anterior or posterior annuls, and the nucleus. Measurements were compared before and after applied creep-loading, as well as in flexed or erect postures. A scale of 1to 4 was used to describe the amount of macroscopic disc degeneration observed.

Results

An increase of disc degeneration from 2 to 4 decreased by 68 percent the amount of pressure in the nucleus, and compressive stress in the annulus was decreased by 48-64 percent, depending on the simulated posture of the segment and the location of the disc. However, anterior annular stress gradients showed an average 75 percent increase in the flexion position, and posterior annular stress gradients increased 108 percent in upright posture.

Conclusion

The neural-arch provides stress-shielding, but compressive stress gradients are significantly increased with an increasing grade of disc degeneration. Adjacent lamellae are sheared by the stress gradients, which may contribute to the delamination and collapse of the annulus.

Summary
Delamination of the annulus and reduction in nuclear pulposus pressure
Article Name
Delamination of the annulus and reduction in nuclear pulposus pressure
Description
Stress-shielding by neural arch is important as is the stress gradients through the lamellae play a part disc collapse of the annulus.
Author
Publisher Name
Dynamic Disc Designs
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