The effect of nucleotomy and the dependence of degeneration of XXXX intervertebral disc strain in axial compression.

@entity1 @entity85 @entity1797
STUDY DESIGN: Biomechanics of @entity1 intervertebral discs before and after nucleotomy. OBJECTIVE: To noninvasively quantify the effect of nucleotomy on internal strains under axial compression in flexion, neutral, and extension positions, and to determine whether the change in strains depended on degeneration. SUMMARY OF BACKGROUND DATA: Herniation and nucleotomy may accelerate the progression of @entity1797 . Removal of nucleus pulposus (NP) tissue has resulted in altered disc mechanics in vitro, including a decrease in internal pressure and an increase in the deformations at physiologically relevant strains. We recently presented a technique to quantify internal disc strains using magnetic resonance imaging (MRI). METHODS: Degeneration was quantitatively assessed by the T1   relaxation time in the NP. Samples were prepared from @entity1 levels L3-L4 and/or L4-L5. A 1000-N compressive load was applied while in the magnetic resonance scanner. Nucleotomy was performed by removing 2 g of NP through the posterior-lateral annulus fibrosus (AF). The discs were rehydrated, reimaged, and retested. The analyzed parameters include @entity85 , AF radial bulge, and strains. RESULTS.: The @entity85 was more compressive after nucleotomy. In the neutral position, the @entity85 after nucleotomy correlated with degeneration (as quantified by T1   in the NP), with minimal alteration in nondegenerated discs. Nucleotomy altered the radial displacements and strains in the neutral position, such that the inner AF radial bulge decreased and the radial strains were more tensile in the lateral AF and less tensile in the posterior AF. In the bending loading positions the radial strains were not affected by nucleotomy. CONCLUSION: Nucleotomy alters the internal radial and axial AF strains in the neutral position, which may leave the AF vulnerable to damage and microfractures. In bending, the effects of nucleotomy were minimal, likely due to more of the applied load being directed over the AF. Some of the nucleotomy effects are modulated by degeneration, where the mechanical effect of nucleotomy was magnified in degenerated discs and may further induce mechanical damage and degeneration.
