Animal models to understand the human lumbar intervertebral disc is an important topic. Recently, Wilke et al. looked at intradiscal pressures during daily activities in sheep-one of the most comparable animal models to humans.
Back pain is most linked to intervertebral disc degeneration which includes proteoglycan loss with accompanying water loss as well as disc height loss. But to understand the complexities of this, ethical approval to use humans in an in-vivo setting is challenging. Therefore, animal models have been and will continue to be a useful way to understand the internal aspect of the disc.
These researchers embedded a pressure transducer within the nucleus at the L2-3 and L4-5 levels of this animal. They then divided the measures into two main categories: active phase and rest phase. This was an arbitrary division because sheep do not have the same rest schedules as humans do. Interestingly, they found that intradiscal pressures were on average two to four times higher compared to humans. One would think because of their quadruped orientation and horizontal nature of the spine, the pressures would have thought to be less. This was not the case. Some of the ideas around why this was the case included the active muscular contraction of the longitudinal muscles to keep the forelimbs and hind-limbs in approximation with one another. In other words, if the distance between forelimbs and hind-limbs increased, the spine would sag.
Another interesting finding was they found intradiscal pressures lowest during the surgical procedure. They hypothesized that it was the medication that may have caused the muscles to relax and thus reduce the intradiscal pressures. Conversely and postoperatively, the pressures were highest. Clinically, could the effect of muscle relaxants help reduce intradiscal pressures in humans? This could likely be the pharmaco-mechanical mechanism in prescribing muscle relaxants in humans but still requires supporting research.
Overall, research like this is fundamental if we are to use animal models to study human intervertebal disc. Dynamic Disc Designs is committed to highlight fundamental research in the spirit of fostering research ideas to improve outcomes. Our spine education models help facilitate discussion.