This is Part II, describing the competing technologies of nucleus regeneration (ADCT) and nucleus replacement (PDN).
ADCT
ADCT, autologous disc (or disc-derived) chondrocyte transplantation, is a procedure where cells from the patient's nucleus are removed, cultured in a lab and then inserted into the nucleus of the degenerated disc. It is often done in conjunction with a discectomy, where discectomy is indicated to address a herniation. "Chondrocytes" are cells that produce proteoglycans. Proteoglycans are hydrophilic: they are the substance that sucks water into the nucleus to give it its strength and turgidity, and also to create the pump effect (water expressed from the disc when loaded, sucked back in when rehydrated) that serves to transport nutrients and wastes to and from the vertebral endplates.
Obviously, the theory behind ADCT is that the nucleus has degenerated because of the decline in the number of chondrocytes that produce the essential proteoglycans, and upping their numbers will restore the nucleus to healthier function. This may seem far-fetched, but in fact there's a fairly impressive track record being built with similar therapies to repair/regenerate other joint tissues, such as knee cartilage. (Those tissues are also chondrocytes; this technology goes by the acronym "ACT," for "[generic] autologous chondrocyte transplantation.") And given that the nucleus is mostly water any way, with the living cells comprising only .25 to .5%, nucleus regeneration through transplantation of chondrocytes would seem to have a good chance for success.
The best quick source for information is the website of Co.don, a German company at the forefront of marketing the cell biology technology (they do the cell culturing). Their marketing rep is also very good at responding to email questions. Email address and website are:
info@codon.de
http://www.codon.de/_/
There are two procedures involved in ADCT, one to harvest and one to implant. If done in conjunction with a discectomy, the material removed in the discectomy is used for the culture. Implantation takes places about three months after the discectomy, to give the annulus time to heal. At implantation, the disc is first pressure-tested to make sure the annulus is competent enough to proceed.
If not done in conjunction with a discectomy, the recruited cells are (I believe should be) harvested from healthy discs, to lessen the trauma to the vulnerable disc. The time needed for culturing the cells in the lab is two to four weeks, so that would be the minimum time between procedures. Presumably, you could pressure-test the disc in the first procedure, to determine up front if you are not a candidate.
Improvement comes gradually over a few months.
From what I can tell (and that is what the Co.don representative told me), you'd have to go to Germany for this procedure (two trips or one long stay).
PDN
Prosthetic Disc Nucleus replacement entails removing the nucleus and implanting a prosthetic device intended to mimic the natural function of the nucleus.
There are a mind-numbing array of different PDN devices, in various stages of development, trials and use. You thought it was frustrating trying to decide between a charite and a pro disc? Hanh!
There are two basic kinds of PDN, prefab devices that are inserted (usually in a dehydrated state) into the disc, and fluids that are injected, and then cure in the disc. Among the prefabs, there are design differences such as unconstrained versus constrained (surrounded by a web envelop to hold in shape, and in place); differences in materials used; and differences in shape and size. One device is a spiral coil, which allows the device to exert a mechanical tension on the annulus.
The materials/devices that interest me the most are the hydrogels, a material that has hydrophilic properties, and thus act like the proteoglycans of the natural nucleus. While all the devices strive for a soft, elastic pillow that mimics the cushioning provided by a normal nucleus, and all the devices appear to absorb water, it is not clear to me (at least there is no claim) that all the devices also serve the function of transporting wastes/nutrients through the disc. The hydrogels do make this claim: "The hydrogel's ability to rehydrate itself mimics an important characteristic of an intact nucleus pulposus [namely, pumping up at night, and pumping fluid out during the day]... The "pumping action" of the hydrogel closely mimics the nutrient cycle that is constantly ongoing in a natural disc." "The value of the Neudisc and PDN hydrogel technology is the ability to mimic the intact nuclear material's ability to "uptake" water, continuing the nutrient cycle through the vertebral endplates."
Next, there is an even more bewildering array of options for implantation of the device (both in device design and surgical procedure)--the issue that so far has been the achilles heel of this technology. On the subject of implantation, the injectable prosthetics have the obvious advantage of a less invasive procedure, smaller annulotomy and possibly also maximize fit, and minimize the risk of migration after surgery.
Nucleus replacement has been around for about 10 years. Some devices have their European CE mark. There are at least two investigational trials now underway in the US. One note of caution if you pursue inclusion in a US trial: injectable PDNs (like ADCT) have been most often used in conjunction with discectomies. When used as an adjunt to discectomy, they only inject enough to replace the material removed for the herniation, they don't replace the entire nucleus. Unless I'm reading incorrectly, it appears the injectables will be tried out for total nucleus replacement too. The US trials going on right now, tho, are only for partial replacement as an adjunct to discectomy.
Even with the least invasive, injectable PDN, this is a far more invasive procedure than a simple injection. Among other things, remember, the nucleus has to be removed, which will require endoscopic instrumentation.