Abstract
Introduction
Intervertebral disc degeneration has been associated with low back pain (LBP) which is a major cause of long-term disability worldwide. Observed mechanical and biological modifications have been related to decreased water content.
Clinical traction protocols as part of LBP management have shown positive outcomes. However, the underlying mechanical and biological processes are still unknown.
The study purpose was to evaluate the impact of unloading through traction on the mechanobiology of healthy bovine tail discs in culture.
Method
We loaded bovine tail discs (n=3/group) 2h/day at 0.2Hz for 3 days, either in dynamic compression (-0.01MPa to -0.2MPa) or in dynamic traction (-0.01MPa to 0.024MPa). In between the dynamic loading sessions, we subjected the discs to static compression loading (-0.048MPa). We assessed biomechanical and biological parameters.
Result
Over the 3 days of loading, disc height decreased upon dynamic compression loading but increased upon unloading. The neutral zone was restored for all samples at the end of the dynamic unloading. Upon dynamic compression, the stiffness increased over time while the hysteresis decreased. Upon dynamic unloading, sulfated glycosaminoglycan (sGAG) release in the medium was lower at the endpoint. In the outer annulus fibrosus (AFo), we saw a higher water/sGAG of at least 30%. In the nucleus pulposus, COL2 mRNA was expressed more highly upon dynamic unloading while MMP3, iNOS and TRPV4 expression levels were lower. In the AFo of the unloading group, COL2 expression was higher but COL1 was lower.
Conclusion
The biomechanical and biological results consistently indicate that dynamic unloading of healthy bovine discs in culture facilitates water uptake and promotes an anti-catabolic response which reflects a function optimization of the disc.
This work combines biomechanical and biological results and opens the door to evidence-based improvement of regenerative protocols for degenerated discs and conservative LBP management.
This study is funded by AO Foundation and AO Spine.
