[sharman]

III Thermal annuloplasty/ablation of granulation tissue

A normal disc is avascular, has no blood supply and, as previously noted, only the outer third of the annulus is innervated (has nerve endings and therefore, pain sensitivity). There is however blood supply to the innervated outer third of the annulus (or just outside? I'm not certain which). Part of the normal inflammatory healing response is neovascularization, the growth of new blood vessels into a wound. The neovascular tissue is 'granulation tissue.' The granulation tissue grows into the annular tear, and the new blood supply brings new nerves with it. A hallmark of disc degeneration is a more vascularization and innervation deeper into the disc than normal.

Annular tears usually develop from the inside out, from the interface with the nucleus (where there is no blood/nerve tissue) out into the outer third. Is that how back pain progresses? The tear first hits the sensitive outer third of the annulus, then neovascularization brings the growth of nerves to the previously insensitive inner annulus? Perhaps the pain mechanism is contact between these new nerves in the tear and the caustic material of the nucleus (a good reason the inner part of the annulus is nerveless in the first place). Perhaps it is simply the multiplication of nerve endings in a wound (the tear) that does not adequately heal. (IMO, mechanical low back pain, pain that increases with activities that load the disc and are relieved with rest, is more likely due to pressure on the innervated tear than chemical toxicity from nuclear material invading the tear. But it could be some of both.)

The body's normal healing process thus apparently works against it with damaged discs, bringing nerve endings to a space where they're likely to encounter chronic irritation.

Thermal annuloplasty

Thermal annuloplasty is the application of heat to the annular tear. The heat causes the tear to shrink (how collagen reacts to heat). It is also hypothesized that the procedure may depopulate the nerve endings in the tear, tho the claim is usually phrased as "maybe" and "partially." The procedure has been done with IDET and discTRODE (same concept, just different heating methods); Yeung does it in conjunction with his SED, with the advantage of being able to view the tear as it's being treated.

I'm leery of thermal annuloplasty. It seems obviously to carry the danger of further damaging the annulus, even when the procedure is visualized and thus more controlled (the surgeon can see the tear react to the heat--is it shrinking or enlarging?), as in Yeung's SED.

IDET has proven disappointing and new studies from Yeung tell us that even patients who enjoy an initially successful result deteriorate again in a few years. (Consistent, by the way, with the mechanism of pain relief being depopulation of nerve fibers--the same as RF ablation of the facets, which also sees improvement eroding when nerves grow back.)

Ablation of granulation tissue.

Now the granulation tissue. Ablation is again the application of heat. Used on granulation tissue, my understanding is that it is akin to cauterizing a wound. I imagine it stops further progression of capillary formation? I can see maybe where that prevents further, more painful deterioration--how does it relieve pain? Do you cure inflammed tissue by heat-blasting it? Frankly, granulation tissue is where I give up. I would truly welcome any insight or info anyone may have into how this tissue plays a role in back pain, and why it's a good idea to ablate it. I am aware of no one but Yeung doing this. And again, I am leery of using heat to alter disc tissues.

IV The Biologicals

Combining biological enhancements is a variation discussed not infrequently in connection with ADCT (that is, the little you see ADCT discussed) and the SpineWave bit I quoted above suggests that they can be combined with PDN as well: "The material [injectable hydrogel] [can be used] as a cell-delivery vehicle for disc repair and reconstruction." [The company is being coy with information, so I'm speculating here. Is the delivery being made to the cells of the annulus and/or endplates (given the nucleus has been removed)? Or is this only intended to be used when their PDN is used as an adjunct to a discectomy, and much of the nucleus remains?)

The notion here is that biological enhancers like growth factors can be embedded into the hydrogel or matrix on which the ADCT cells are grown (the matrix then to be injected with the cells).

I believe there are now clinical trials underway testing intradiscal injection of growth factors as a DDD therapy (at least one in Los Angeles); if that bears out as a therapy, it certainly makes sense to add it to ADCT and possibly PDN. Mark tells me that Dr Garcia in Florida will be starting a trial for intradiscal injection of BMP.

With an ADCT, of course, it will also always be possible to inject biologics at any time--before, maybe during, and certainly months or years after the procedure. With PDN, I don't know. All or most of the PDNs appear to be porous, or at least wet. Can you inject these manmade nucleuses with therapeutic agents, and get them to the annular or endplate tissues you wish to repair?

(And for that matter, to digress, can you do provocative discography on a PDN'd disc? If problems develop down the road, how can you tell if you need to revise the PDN to an ADR or fusion?)

Another possible biologic enhancement for ADCT (now in animal trials at the Cleveland Clinic?) is gene therapy, where through genetic engineering the cultured cells are amped up, so that they produce more of the proteoglycans that keep the nucleus hydrated, and possibly even reproduce more readily. Among other things, this would hopefully combat the senescence that may make an older patient a less good candidate for ADCT.

The final biologic agent in this category is disc prolo, the dextrose solution that is thought to kickstart a healing cycle in the annular tear (which I've tried with some success and some failure). Disc prolo could be done before or after an ADCT, not sure about a PDN.