Post-Myelogram Update

Liz · #1 (**permalink**) 02-26-2009, 08:58 PM

thanks, that's what i thought, i just didn't want to give it away! i've heard Dr. B does that sometimes. Does having it upside down increase wear particles? Also, can you elaborate on the mechanical advantages of this?

mmglobal · #2 (**permalink**) 02-26-2009, 11:54 PM

I'm going to explain what I think the theory is. I am not an engineer. I may be all wet. I can't engage in a discussion about this, I can just pass on what I think I understand.

ProDisc comes with lordotic angles, 6 and 11 degrees. The lower plate that the core snaps in to is flat. The upper plate has the angle. The purpose of the angle is to bring the plates of the prosthesis near parallel.

With the angled plate being the top one, that configuration effectively brings the surface of the upper plate closer to parallel to the lower plate. If the lower endplate is parallel to the floor and the the upper plate is parallel to the lower plate, the ball and socket will have zero sheer force acting upon it (from the pull of gravity... you can load in other ways.) If the upper endplate of the vertebral body is not parallel to the floor, then there will be sheer force acting upon the ball and socket. If you flip the disc, instead of the angled plate bringing the upper plate parallel to the lower plate; the angled plate below will bring the lower plate of the prosthesis closer to parallel to the floor. (Clear as mud?)

It makes sense, but there is a trade-off. I believe that the flipped configuration MAY increase the likelyhood of migration of the lower plate as the sheer force doesn't just disappear. It is reduced on the ball, but I believe it still exists or may even be increased on the lower plate. IMHO, migration used to be a more serious consideration before they got good at sizing, placement and before we had the coated plates. IMHO, while the trade-off needed to be resolved in terms of less risk of migration in the early days of ProDisc, improvements made it more reasonable to work the trade-off towards less sheer force on the actual joint instead of on the bone-metal interface. This should result in less significant wear.

Again... I may be all wet here and may have this completely wrong. Take this for what it's worth... just my layperson's opinion.

Mark

trkdoc714 · #3 (**permalink**) 02-27-2009, 12:41 AM

That was a great explanation Mark. That's actually why I'm not considering any disc with polyurethane inserts. At my age (52) my spine will degrade naturally over time. All of the angles will be altered even if only slightly. The poly cores will not react well to that I fear.

That is one of the properties that makes the Maverick more appealing to me. With a single alloy used in both inferior and superior components, sheer wear is nearly non-existent. If only they offered a zerk fitting for lubrication.......

I had actually emailed Justin when I saw the inverted plate. Thanks for clearing up the mystery of the symetrical endplates.

Bob

johnb · #4 (**permalink**) 02-27-2009, 01:02 AM

I believe if I'd had the DSS and a better diagnosed and addressed decompression procedure, I'd be singing a different and better tune right now. There are many differences between the DSS and the Dynesys. A very important one is the fact that the dynesys is rigid in flexion which is big negative when you think about the implications. IMHO, that affected my situation with low disc height in a very negative manner. I'm 4 months out from removal and I need to update my thread. Mark, I've since read some even newer research on the dynesys and I'd be more than happy to contribute to your PDS discussion. A recent study shows that the dynesys does not slow disc disease and contributes to adjacent disc disease as well. My surgeon confirmed the latter part about the adjacent disc desease as he has seen it in some of his patients where he extended the dynesys. I'll gather up my links an update my progress and my thread as my own case may be of some help to others.

I want to thank Justin for sharing his situation with us so we can all learn and become more empowered regarding our own situations.

mmglobal · #5 (**permalink**) 02-27-2009, 01:28 AM

Bob, we all have to pick what we are afraid of. See the video of me playing tennis with Charite' pt. number 1 from 1984, before they new about oxidation, sterilization, packaging issues with poly, sizing, placement, etc.... Why would you be more afraid of poly wear as related to sheer force than metal ions? We reduce the risk of wear being an issue by getting a proper installation. For me, revisability is more of an issue than wear. Explanting a Maverick at L4-5 is much more difficult than a poly core device. Having said all that, I believe that properly implanted in a properly selected patient, they will all work fine. Avoiding improper implantation is the key to success.

John, rigidity in flexion depends on the tensioning of the cord. Extension limits depend on the size and retained rigidity of the spacer. Not all are fixed.

Dynesys results vary so greatly from one surgeon to the next. Some surgeons report 25% screw breakage/loosening, while others report zero or close to zero. Application of Dynesys for varying inidications has also been all over the place. I look forward to your update... I hope it's good.

I agree... thanks to Justin... this gives us an opportunity to learn a ton.

Mark

treefrog · #6 (**permalink**) 02-27-2009, 05:43 PM

Quote:

Originally Posted by mmglobal

Avoiding improper implantation is the key to success.

I agree... thanks to Justin... this gives us an opportunity to learn a ton.

Mark

Which is why I want to have Dr. B's opinion (and probably surgeon) on my back. I believe he, better than almost anyone else, will be able to tell me if and what type of surgery is best for me.

I don't know if Justin is too thrilled to be the subject of our learning opportunity though.

Justin · #7 (**permalink**) 03-05-2009, 03:18 PM

Before my hiatus on the forum, I wanted to give everyone an update as to not leave you guys hanging.

About the Surgery: the DSS technology looks very promising to me. From the publications I've read about the system in biomechanic journals, the studies look good and the DSS is accomplishing what it is intended to do (decrease unnatural flexion and extension of the spine). This device looks like it will work well in concert with my 2-level ADR. I know it hasn't been studied extensively, but the DSS design is based on -- unfortunately -- the failures of stabilization devices that are "too rigid" such as the Dynesys (sorry for everything you been through John). A plus in theory to this device is the relatively easy conversion to a "traditional" fusion (the dynamic coupler that is attached to the two screws would just be swapped out).

The surgery would last about 2 hours with ~3-6 day hospital stay. Cost around $26k.

Goal of the Surgery: to remove as much as the osteophyte as possible given difficult access and stabilize the spine minimizing the L4 anterolisthesis. This would relieve the compression on the cauda equina and nerve roots--hopefully reducing/eliminating my bilateral leg pain.

Surgery Date: the surgery is elective. This means the limiting factors are how much pain I can endure and if there are any signs of paralysis.

Recovery / Prognosis: Drs. Fenk-Mayer and Bertagnoli could not give me a definitive on this, which is completely understandable regarding my past surgical history, etc. Dr. F-M did say that I would be able to "take longer walks around the 3 week mark."

The Positives: I had a cervical MRI that came back clean before the new year and the rest of my lumbar spine looks really good. Most of my back problems have been the result of trauma, not widespread "genetic DDD."

$26k is a lot for a poor, extremely in debt student.