M6-C Limitations

[brookscw]

For anyone out there that has done a lot of research, or has had ADR with the M6-C, I was wondering what limitations either you'd been advised about, or discovered post-surgery. From the doctors that I've spoken with that favor it, they present the M6 as the magical silver bullet...all up-side, and no down-side. It's almost like it's a bit too good to be true. From the research that I've done, and from what I've been told, it would seem to correct the potential issues that the ball-in-socket discs have (e.g. ProDisc, Prestige) when they put too much pressure on the facet joints due to the unconstrained rotation they have, and the lack of horizontal, lateral and vertical movement which places added stress on the adjacent levels. They also claim to have solved the problem the Bryan disc had where it would calcify about 12% of the time (I think that's the right term).

I've been told by one doctor that he knew of only one M6-C failure, and that was because there was a fusion at an adjacent level, so they suspect the additional stress at the ADR level was the cause. Has anyone else heard of any failures? I know in the early stages, there were problems with the available sizes of the implants and there was some trial and error with getting the right placement, but am I correct in assuming those issues have been corrected? What are the consequences if the M6-C fails? Obviously a revision would be in order, but are there any other concerns? For instance, if it fails, you have a 25% chance of being paralyzed, or something crazy like that?

If anyone has any literature that they might have found on the M6-C, I would very much appreciate a few links if possible. I've seen references where people said they have read this or that, but nothing substantial. Almost all of my information has come from doctors that I've spoken with, or from forums like this.

Thanks!

p.s. I don't have my sig up yet, but I'm potentially looking at a 2-level ADR, C5-C7.

[Katie]

Welcome brook! I probably would have gone with the M6 if not for metal allergy problems. It sounded pretty good to me too.

I ended up instead with the Nuvasive NeoDisc, an ADR with a very simple design that has been a great success with me so far. It is a silicone disc covered with a poly mesh that eventually bonds to the bone of the vertebrae. So the disc itself is free to move. My neurological problems have all disappeared and I suspect if there were ever any problems in the future, that revision surgery would me much simpler than any ADR with a keel that is embedded in the vertebrae.

The NeoDisc is not well known yet in North America, but has been used extensively by the surgeon I went to, Dr. Luiz Pimenta in Brazil. It is manufactured in California though.

I just wanted to let you know that it exists The M6, ProDisc, etc. are used more often in the US and Europe, but I think with time the NeoDisc will gain in popularity. There are some good articles here on the forum if you'd like to do some research.

I hope you get some good answers to your initial questions.

[Carson]

We take our chances with any and all devices. There is no magic bullet as you know. There is no perfect procedure or device. All devices have limitations of some sort compared to a natural disc. We're still very early on amidst the ADR time line.

All we can do is put forth due diligence in researching the available procedures, research the devices that facilitate those procedures, research the surgeons and the clinics that offer them and ultimately address the problem as best we can in a timely (relative to your condition) fashion.

Now 2011, I see no reason to use discs that were being used in 2002. All discs have limitations (negatives) but if asking for opinions than I'd agree with Katie above; the M6-C or Neo Disc would be the choice I would make based on my own unique condition, age, and what my doctor has discussed with me.

In my opinion, if Synthes (Pro-Disc) had their way they'd be the sole manufacturer of artificial discs for the next 100 years. I do not like their approach to business and, again, in my opinion, their aggressive patents have constricted the progress of better designs by competing companies.

[JPJH]

I've had my two level M-6 at C 4/5 & 5/6 for 6 months now and so far so good. Had it done by Dr. Clavel in Barcelona. Range of motion is fantastic, better than before surgery. Had some PT when I got home to work on strengthing some back muscles. The PT, who has worked with a bunch of fusion patients as well as several Pro-Disc patients could not believe the range of motion I had with the M-6. You're right not much out there about failures with the M-6, but anything is possible with any surgery. But for now the M-6 it the hot ticket. I'm sure like all things something new will come along, but when you are at that moment where you just can't put the surgery off anymore you just have to take a look at the options that are currently available and make the best possible choice for you at that time. Best of luck to you.

JPJH

[jss]

Brook,

I have two cervical fusions and two M6-C's, one above the adjacent fusions, and one below. This week I'll have had the M6's for 17 months and as of yet have been blessed with no problems.

I was given no limitations unique to the M6, but was concerned that it might not be SCUBA friendly. A medical device engineer on this site has assured me that even in the worst case scenario that SCUBA would not present a problem.

I wouldn't consider the M6 a "silver bullet" because it comes with many of the same post-surgery limitations common with all other ADR devices; but the M6 was specifically designed to address all of the problems, like the ones you mentioned, created by the ball-and-socket type devices. I've not yet heard of an M6 failure, but have seen posted two cases where M6's had to be explanted. In one case an osteophyte had begun growing into the neural foramen at the operative level, and in the other the patient was not an ADR candidate and should have undergone fusion to start with.

I've not heard any figures on probability of certain types of injuries on an M6 failure, but the M6-C has only been in widespread use for about six years. I don't doubt that there have been failures. A concern I do have with the M6 is infection. That is a concern with all ADRs, but to me seems would be much more problematic in the M6 (and NeoDisc).

Good luck, Jeff

[brookscw]

Thank you all for your replies! It's so great to be able to speak with people who have experience with these devices and not have to solely rely on a surgeon's advice. Not that I don't trust surgeons, but generally they aren't the ones having to live with the implants, so they may not always understand completely.

@Jeff

What are some of the post-surgery limitations you've been told? I've heard from a German doctor that, within reason (whatever that means), there are no restrictions, and from Dr. Boeree that bungee-jumping and trampolining are not advisable, but those were the only two specific examples he gave me. At the same time, he also said roller coasters were ok, so I'm not sure why trampolining would be so bad.

I'm also an avid SCUBA'er...one of my favorite things to do is spearfishing, which often involves dives up to 110'. Why did you have concerns about the M6 with regard to SCUBA? Was it because there are air pockets in the device? If you can remember, why did the medical device engineer say not to worry? I've read every article on this site that has the word M6 in it, but I didn't see that thread for some reason. As long as the air pockets are relatively small and the outer sheath is stretchable (which I'm almost positive it is), then I would think it would be ok. Was there another concern you had?

Also, why would you expect the M6 and NeoDisc to have a greater risk of infection than other types of implants?

[jss]

Brook,

I was given no post-surgery limitations. The only post-surgery limitation that I've read that my surgeon (Dr Pablo Clavel, Barcelona, Spain) has ever given anyone was to contra-indicate contact sports. I have many self imposed limitations because they seem prudent.

• No driving my 67 Mustang (no head rest)
• No roller coasters (too many very sharp ... bumps and jerks)
• No more firing big bore rifles (will miss a moose hunt this winter)
• No more snow skiing

I haven't attempted a trampoline or bungee jumping since surgery ... but that sounds intriguing. Given Dr Boeree's words, perhaps I'll do a roller coaster again?

I'll address the SCUBA and infection issues in separate posts (they're quite long).

Jeff

[jss]

Brook,

My concern with SCUBA ...

Per the engineers at Spinal Kinetics there are two vent holes in the polymer sheath on the M6 that let our lymph fluid flow into and out of the implant. The purpose of the sheath is to contain wear debris from the implant. As a diver yourself you know that at depths below 33ft that our blood, lymph and all tissues will have nitrogen dissolve into them at levels higher than those at one atmosphere; and that as we ascend that nitrogen will leave the solution of our fluids and can form bubbles of nitrogen. If there is enough nitrogen leaving the solution of our fluids at once then the bubbles can become large enough to cause problems; severe pain and even death.

The scenario with which I was concerned was this. When the lymph that has vented into the M6 is saturated with nitrogen, and I begin to ascend, that nitrogen will come out of my lymph solution to form bubbles; and because a gas bubble takes up more physical space than lymph fluid, this will cause an outflow of lymph from the implant. The outflow of of lymph would cause movement of the wear debris trapped inside the implant and potentially stop of the two vent holes in the polymer sheath; causing the M6 to now be air tight; something that it was not designed to withstand. As I continue to ascend and then walk around for some hours on the boat/beach, more nitrogen comes out of the solution of my lymph inside the air tight M6, causing the sheath to swell. Would that swell damage the sheath? Would it swell enough to push on my spinal cord or root nerve? Or force wear debris through the vent holes? That was my concern.

The medical device engineer (his handle was MDE) knew how to calculate nitrogen saturation levels in blood, lymph, etc... He assured me that in that scenario that the sheath would swell less than 1mm. He assured me that my spinal cord and root nerves were more than 0.5mm from the sheath of the M6 and then, based on his familiarity with the materials of the sheath stated a confidence that the sheath would not be damaged by that amount of swelling.

Make sense?

Since time I've been diving only once. The maximum depth was 48 feet and I experienced no issues. I plan to dive the Santa Rosa Wall in Cozumel again this summer; which is a depth of 85-100 feet. Sure hope that MDE was right!

Jeff

[jss]

Brook,

My concern with the M6 (and NeoDisc) regarding infection...

When we have any part of our anatomy removed, like an intervertebral disc, we have our capacity to mount an immediate immune response in that area removed as well. Meaning that if a foreign body invades, like a bacteria, that the immune response must come from other parts of our body. Macrophages, mast cells, antibodies, b-cells, t-cells, lymphocytes, etc... have to migrate with the flow of our lymph fluid to the infected area before they can begin to either kill the invaders or signal our immune system that there is an invader. (google chemotaxis)

Unlike most ball-and-socket designs, the M6 and NeoDisc allow much slower access of lymph, and thus our immune response to the inside components of those devices because they are mostly sealed. So our immune system will have a much harder time reaching and eradicating an infection that becomes established inside one of those prosthesis than if such an infection tried to establish within a ProDisc or especially a Prestige.

When a bacterial colony grows to a certain size it will begin to behave differently than a smaller colony. This is how staphylococcus aureus in a kotex was able to kill young women in their periods in the late 70's and early 80s via "toxic shock syndrome". (google quorum sensing)

If you opt for ADR, especially if you choose an M6 or NeoDisc, I would encourage you to be vigilant concerning bacterial diseases. When medical questionnaires ask if you have any artificial joints, this problem is why they are asking. When I go to the dentist, when I get into the chair I always remind them that I have two artificial joints. To date the dentist has always asked where, and then disappeared from the room only to return with an antibiotic.

Make sense?

Jeff

[brookscw]

I have seen recommendations that you should take antibiotics before and after a dental cleaning (or any other dental work for that matter) to guard against infection no matter what implant you get. It makes sense that if an infection did get inside the sheath somehow, it might be harder to squash than with another type of implant. I wasn't aware that the sheath had vent holes. Wonder why they just didn't vacuum out the air and seal it up?

It makes sense now that you might have been concerned about the nitrogen buildup in the lymph fluid. From what I've read though, I haven't seen a lot of evidence that would suggest there is a lot of wear debris contained within the sheath. Have you been told differently? Do you know the size of the holes relative to the debris? I would think the holes getting plugged would be an issue if the debris is big enough just with the lymph fluid sloshing around. Anyway, assuming you are doing things correctly, in theory at least, the nitrogen should never get the chance to bubble. However, that dynamic might change since the flow of liquids is different within the implant than it would be around a normal disc.

Aside: If you don't dive with nitrox yet (basically any mixture that has better than 21% O2), then I would strongly recommend it. You'll have to do a check-in-the-box class and checkout dive (they're both a joke because all modern dive computers have nitrox tables now, and all you really need to know is your depth limit with a given mixture), and it's a little more expensive than air (maybe $5-10/tank), but way, way safer and you can stay down longer at depths around 85-100'. Like I mentioned, it has a hard bottom limit (you're pretty much dead-meat if you go below your mixture's max operating depth), so you'd have to be extra vigilant on a wall dive, but in the case where you are already concerned about nitrogen absorption, any way to decrease that would be a good thing the way I see it.

Also, I'm not sure I understand your numbers...MDE said the sheath was at least .5mm away from all important structures, but it should only bulge 1mm, so there shouldn't be an issue. My math says there definitely might be a problem in a worst case scenario, so hopefully you've got a decimal in the wrong place...