What is the pathology behind disc degeneration?
In disc degeneration, the matrix of the disc can no longer function normally because the extra cellular matrix (ECM) becomes degraded, losing some molecules, particularly proteoglycans and their constituent glycosaminoglycans. This process almost certainly involves the resident cells within the disc. While we know quite a lot about different enzymes and other molecules that can be involved, the exact sequence of events and trigger factors are not always clear. I suspect there may be many different pathways resulting in a similar endpoint. As with so many other things, our genes play a significant part in whether degeneration will happen or not.
What are the ways that cell therapy is being proposed as a treatment for disc regeneration?
It has not just been proposed—it has already been used in patients! For example, autologous cells from herniated discs cultured in vitro and injected back into the disc has been performed for some years in Germany, and mesenchymal stem cells from the patient’s bone marrow have been injected into discs in the USA and Japan.
Meantime, there are many aspects of cell therapy that are being researched, such as: attempting to identify the best cell type to use and whether this should be autologous or allogeneic; whether cells should be from the annulus fibrosus or nucleus pulposus; or whether they should be stem cells and if so from where—bone marrow or adipose tissue or somewhere else?; and should a carrier or scaffold be used?
What questions do we need to answer before we can routinely use cell therapy to treat disc degeneration?
A very important question is “which patients would benefit most from such treatment?” For example, should you select only very degenerate discs to treat? If so, the rest of the spinal structure, nutrient pathways, vascularisation etc. may not be able to support the implanted cells. But then would surgeons be happy to treat, and would patients want to have cells implanted into discs, if the degeneration (or more importantly, the pain) was not too bad?
More recently another big question has been raised and this is about how the cells should be introduced to the disc. I believe most people imagined, until a couple of years ago, that cells could be injected (minimally invasively) into the discs, but there are now several studies indicating that a needle hole, however small, may be very bad news for the disc long term and such a “puncture” can actually contribute to degeneration of the disc.
What role can spinal surgeons play in helping to answer these questions?
They can help researchers by providing clear grouping of (or characterising) patients in terms of diagnoses and phenotyping. They can work with scientists and other researchers in providing:
- Ideas and hypotheses to test
- Surgical samples for scientific investigations
- Being active in collaborative studies
These factors are really important to progressing the field of research in disc degeneration.