Effect of circumferential constraint on nucleus pulposus tissue in vitro.

BACKGROUND CONTEXT

Degeneration of the intervertebral disc (IVD) involves structural changes in the annulus fibrosus (AF), which could alter the mechanical forces imposed on the nucleus pulposus (NP) tissue. This could contribute to degenerative changes that occur in the NP.

PURPOSE

The purpose of the study was to determine whether circumferential constraint affects anabolic and catabolic gene expression, biochemical composition, and mechanical properties of NP tissue.

STUDY DESIGN

Nucleus pulposus cells were isolated from bovine caudal IVD and allowed to form tissue for a period of two weeks. The effect of no, intermediate, or high circumferential constraint on biochemical composition (cellularity and proteoglycan and collagen synthesis), gene expression, and compressive mechanical properties was evaluated.

RESULTS

Increasing the rigidity of circumferential constraint surrounding in vitro formed NP tissue resulted in decreased gene expression of aggrecan and type II collagen and increased expression of MMP-1 and ADAMTS-5. This was associated with decreased accumulation of extracellular matrix and a deterioration of the compressive mechanical properties of the tissue.

CONCLUSIONS

As increased circumferential constraint can have a significant negative effect on the composition and quality of NP tissue and this raises the possibility that the AF may contribute to the degenerative or age-related alterations that occur in the NP. Further study in a functional spinal unit is required to validate this.