[sharman]

RISKS

1) How much trauma is caused by the implantation procedure (remember, the annulus is left in place).

The ADCT procedure is very minimally invasive. I believe both the harvesting and the implantation can be done through a needle, or small, blunt-tip cannula that causes minimal trauma to the annulus.

PDN, on the other hand. The first generation devices had high failure rates due to migration/extrusion out of the annulotomy, as well as subsidence into the endplates (due to poor fit with the endplates? due to the device being harder than a natural nucleus?) Several new implant designs, as well as redesigned surgical procedures, have been advanced and are still in trial and development phases. Reportedly, the new procedures have brought the implant failure rate down for Raymedica's PDN, but not solved the problem completely.

PDN is inherently more invasive than ADCT. The removal of the nucleus as the necessary first step is not a simple thing, judging from the discussion about techniques and surgical tools to effect this step. As for implantation of the device, it would seem that the injectable PDNs have an advantage, requiring smaller incisions/annulotomies, and possibly resulting in better fit and adherence.

2) Any risks associated with the materials? Toxicity, particulate wear, allergies?

ADCT obviously uses only the patient's cells and so compares favorably to foreign implants in this category.

PDNs appear to use materials well tested for biocompatibility. Unlike ADRs, there is no friction or hard surface that could result in particulate wear over time.

3) Any reported ill effects? How many patients have had the device implanted, and how long have they been walking around with it?

I'm not aware of any reports of ADCT causing complications, side effects, etc. There are the usual risks of the surgery. The first implant group was in 1996. I think I remember reading that about 250 patients total have had the procedure, but I cannot find that reference now, so I may be dreaming it. In the very similar technology of chondrocyte transplantation for other joints (e.g., knee cartilage repair), there is a good history of safety.

With PDNs, the big stumbling block has been implantation of the device. Early generations of the surgery had a high rate of migration of the device outside the annulus, subsidence into the endplates, etc. The latest products and procedures display a wide array of new approaches, which will hopefully eliminate such risks, or reduce them to minimal. But, we still don't know.

It appears that, once you get past the hurdle of implantation, PDNs have a good track record on safety (10 years) for patients who've been walking around with them for many years.

4) Might it wear out and need replacement?

There is a theoretical likelihood that the benefits of ADCT will fade over time, at least for older patients, due to cell senescence. However, unlike a foreign device that, if failed, must be removed or worked around (e.g., if an ADR wears out), ADCT does not create future problems not inherent in normal disc degeneration any way.

There is no clinical evidence either way yet, but it would seem theoretically possible that a PDN could wear out, or degrade over time.

5) Is it revisable if things go wrong?

Obviously, there have been many PDN revisions--but I can't quite figure out from the literature what they've done with those patients who've required "a second surgery" or "revision" if the implantation fails. Do they implant a second PDN? Revise to fusion or ADR? Obviously, they can't unscramble the egg.

6) Is there damage if things go wrong?

It seems like a failed PDN implantation could cause collateral damage--e.g., damage the nerve root if the device migrates outside the annulus. Are endplates damaged when there's subsidence? I could find little info.

7) Does it burn bridges for further surgeries?

Neither ADCT nor PDN would rule out future fusion or ADR at the same or other levels.