Intradiscal Pressures 1

Animal models to understand the human lumbar intervertebral disc.

intradiscal pressures in sheep

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, including proteoglycan loss with accompanying water loss and 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 helpful way to understand the internal aspect of the disc.

Disc degeneration is regarded as one of the major causes of persistent low back pain. It is believed to be connected with structural changes, including a gradual breakdown of proteoglycans and a steady loss of intervertebral disc height and water content. A better understanding of disc function and technical advances in tissue engineering have resulted in several ways to repair or regenerate different disc compartments following herniation or in the early phases of painful disc degeneration over the past two decades. Based on this approach, some have worked to implant cellular scaffolds to stimulate differentiated in situ regeneration of the structurally altered major disc compartments, the nucleus pulposus and annulus fibrosus. However, extensive preclinical testing is required to demonstrate the safety and efficacy of any new therapeutic option before any of these strategies can be implemented clinically. Models of large animals are particularly helpful for assessing the feasibility and practicability of numerous surgical operations.

Sheep have been increasingly used as animal models for intervertebral disc studies since the early 1990s. In early in vivo investigations, the structural similarities between humans and sheep were used to justify the use of sheep. Comparative biomechanical and anatomical research proved that humans and sheep are comparable. Because biological factors, such as the disc’s cellular and biochemical makeup, were also similar between species, it was established that the sheep represents a valid in vivo model for disc regeneration procedures. Biomechanically, however, it is still controversial whether animal models should be used or not for spinal research. Due to the upright position of humans, quadrupeds do not appear to be suitable as representative in vivo models for spinal applications and, consequently, for disc regeneration procedures. Reliable in vivo data, however, are still missing. Intradiscal pressure (IDP), an essential biomechanical parameter for the cellular differentiation of the disc, has never been studied in sheep in vivo and compared to humans. To give a full physiological understanding of the ovine intervertebral disc, the current work by Wilke et al. aimed to assess the IDP throughout 24 hours in vivo. Two intervertebral discs, L2-L3 and L4-L5, were studied to assess any potential dependence of IDP on the spinal level. The IDP measures of sheep were compared to previously published human data and aided in the scientific interpretation of past and future sheep investigations.

These researchers embedded a pressure transducer within the nucleus at this animal’s L2-3 and L4-5 levels. 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 than humans. One would think because of their quadruped orientation and the horizontal nature of the spine, the pressures would have been considered to be less. This was not the case. Some 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, the spine would sag if the distance between the forelimbs and hind-limbs increased.

Another interesting finding was they found intradiscal pressures lowest during the surgical procedure. They hypothesized that the medication may have caused the muscles to relax and thus reduce 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 it still requires supporting research.

Overall, research like this is fundamental if we use animal models to study human intervertebral discs. Dynamic Disc Designs is committed to highlighting fundamental research to foster research ideas to improve outcomes. Our spine education models help facilitate discussion.

Dynamic Disc Designs

At Dynamic Disc Designs, we create models demonstrating disc dynamics that can include both an annulus and a nucleus. With this unique and much-needed designs, now education can include the discussion of intradiscal pressures and how it relates to the biomechanics of a spinal motion segment. Explore