[General Spine] Medical Device Engineer to answer questions you may have

[MDE]

Hello

That is correct herniated disc at both levels L5-S1 complete disc removed and bone material implanted L4-L5 Micro Disc with no implants. I was told at my first appointment to have Staxx xd implants never happened I suspect it was not covered with insurance?

Thank You

Gil

Obviously you're still less than 6 months post op so there is definitely still some recovery time. Has your surgeon determined which level is potentially causing the lingering issues?

Completely armchair quarterbacking here, but I would bet that it's the level that did not receive a complete discectomy. It's possible that over time the additional support will allow this disc to heal, which may take some time (obviously not what you want to hear). Unfortunately it's almost impossible to know for sure whether a disc will heal or just continue to degenerate after a microdiscectomy. The most telling covariant is age (younger the better).

[Susan.303]

Hello MDE,
I'm new to this forum, and may be going about this incorrectly....but I had asked if there were any devices in the works to add some flexibility for scoliosis fusions (I know this is a contradiction in terms, but I hope you understand the gist). Am I correct that your lack of a direct response is because fusion is the only option for scoliosis and nothing is being worked on to grant these long multiple level fusions any flexibility even at the two ends of a long fusion or at sacrum or hip?

Thanks,
Susan

[MDE]

Hello MDE,
I'm new to this forum, and may be going about this incorrectly....but I had asked if there were any devices in the works to add some flexibility for scoliosis fusions (I know this is a contradiction in terms, but I hope you understand the gist). Am I correct that your lack of a direct response is because fusion is the only option for scoliosis and nothing is being worked on to grant these long multiple level fusions any flexibility even at the two ends of a long fusion or at sacrum or hip?

Thanks,
Susan

Sorry for my delay in response. I'm trying to research this as it's an area I'm not familiar with. My gut instinct is that there isn't, based on the known physiological loads with adult scoliosis, I think it has to be a rigid construct. I Know there are some shrinking scapula rods, however I believe these are typically used in pediatric cases. Let me research this a bit more, and I'll get back to you.

[Susan.303]

Sorry for my delay in response. I'm trying to research this as it's an area I'm not familiar with. My gut instinct is that there isn't, based on the known physiological loads with adult scoliosis, I think it has to be a rigid construct. I Know there are some shrinking scapula rods, however I believe these are typically used in pediatric cases. Let me research this a bit more, and I'll get back to you.

Thanks MDE. I think your gut instinct is correct too, but I appreciate your checking into it. The 3-dimensionality of scoliosis curves, dips, bends and twists along with the fact that corrective fusion in adults isn't usually 100 percent correcting, make us unlikely candidates for anything other than fusion. Still scoliosis usually calls for the longest fusions...i.e.: they want to fuse me from T12-S1 and with that many vertebrae fused it sure would make sense to at least do something different at either end of the fusion line to help prevent the extra wear and tear (Obviously I don't speak all the spine terms very well yet). Maybe these long scoliosis fusions could have something more joint like at either end (less so, maybe, in the rib cage area)....or maybe in this age of micro surgery the bracing rods could have small temporary ports included so the Dr. could try adjusting them from the outside, or even running them from the outside, giving the muscles time to adjust to supportting this new form and maximizing the possible amount of correction Prior to fusing. Then after fusion, these exernal rods and temorary ports could more easily be removed....I know, I know, I watched too many episodes of the Jetsons as a child.

As for me…I'm scheduled for a laminotomy and discectomy left at L5-S1 mid January with the hope that the left leg nerve damage will stop so I can walk and stand longer than 5 minutes without doing harm. I'm grateful that I'm still able to work full time and have a great respect for the pain (I don't take pain meds during the day so I know when to sit.) My hope is that I'll then have another 5 years to exercise, swim, strengthen my back and research all my possible options before having to do that fusion. I know the odds are 50/50 that this surgery could make the 15mm left lateral slide I have at L4-L5 worse. For that reason I'm trying to educate myself now to all my options including the likelihood that there aren't many, so again thank you.

[MDE]

Thanks MDE. I think your gut instinct is correct too, but I appreciate your checking into it. The 3-dimensionality of scoliosis curves, dips, bends and twists along with the fact that corrective fusion in adults isn't usually 100 percent correcting, make us unlikely candidates for anything other than fusion. Still scoliosis usually calls for the longest fusions...i.e.: they want to fuse me from T12-S1 and with that many vertebrae fused it sure would make sense to at least do something different at either end of the fusion line to help prevent the extra wear and tear (Obviously I don't speak all the spine terms very well yet). Maybe these long scoliosis fusions could have something more joint like at either end (less so, maybe, in the rib cage area)....or maybe in this age of micro surgery the bracing rods could have small temporary ports included so the Dr. could try adjusting them from the outside, or even running them from the outside, giving the muscles time to adjust to supportting this new form and maximizing the possible amount of correction Prior to fusing. Then after fusion, these exernal rods and temorary ports could more easily be removed....I know, I know, I watched too many episodes of the Jetsons as a child.

What you're talking about (external fixation) is actually something they do a lot in other areas of the body, however it doesn't work very well in spine. There are a lot more negatives to doing something like this in the spine versus a tibia. I'm assuming you've tried using a brace? Obviously braces aren't always effective, but conservative treatment should always bet tried first.

As for me…I'm scheduled for a laminotomy and discectomy left at L5-S1 mid January with the hope that the left leg nerve damage will stop so I can walk and stand longer than 5 minutes without doing harm. I'm grateful that I'm still able to work full time and have a great respect for the pain (I don't take pain meds during the day so I know when to sit.) My hope is that I'll then have another 5 years to exercise, swim, strengthen my back and research all my possible options before having to do that fusion. I know the odds are 50/50 that this surgery could make the 15mm left lateral slide I have at L4-L5 worse. For that reason I'm trying to educate myself now to all my options including the likelihood that there aren't many, so again thank you.

If I was you, I'd also look into some of the alternative scoli treatments including the ones based on trying to "retrain" the neurological control of the muscles. I really am limited in knowledge to the surgical treatments of such pathologies, and I don't want to point you away from surgery as it is probably the right answer, but in the mean time you may want to contact Scoliosis Correction Center - Alternative Scoliosis Treatment to see if this type of intervention helps. Obviously the L5-S1 fusion would still occur, and you'd be doing physical therapy for that, so perhaps you could work with your Physical therapist to try and incorporate some of the scoli treatments into your PT.

The inherent problem with spine surgery is two fold. You never want to operate on a pathology that can be resolved non surgically, but you also see a LOT of literature point to better outcomes when surgery is performed sooner. Surgeons have to balance these data points and manage it on a patient by patient basis.

[Susan.303]

What you're talking about (external fixation) is actually something they do a lot in other areas of the body, however it doesn't work very well in spine. There are a lot more negatives to doing something like this in the spine versus a tibia. I'm assuming you've tried using a brace? Obviously braces aren't always effective, but conservative treatment should always bet tried first.

I never used a brace. Even in my 30s I was told my scoliosis was mild so now that I'm discovering a problem at 51, a brace would only weaken my muscles. I'm with you on conservative measures. I did just engage a chiropractor to assist me in gently unlocking my ribcage and neck area. My hope is that this upcoming Laminotomy and Discectomy L5-S1 will buy me some PT years before looking at fusion so I can also strengthen the Lumbars.


If I was you, I'd also look into some of the alternative scoli treatments including the ones based on trying to "retrain" the neurological control of the muscles. I really am limited in knowledge to the surgical treatments of such pathologies, and I don't want to point you away from surgery as it is probably the right answer, but in the mean time you may want to contact Scoliosis Correction Center - Alternative Scoliosis Treatment to see if this type of intervention helps. Obviously the L5-S1 fusion would still occur, and you'd be doing physical therapy for that, so perhaps you could work with your Physical therapist to try and incorporate some of the scoli treatments into your PT.

Thanks for the Scoliosis Correction Center link. I'll look into it.

The inherent problem with spine surgery is two fold. You never want to operate on a pathology that can be resolved non surgically, but you also see a LOT of literature point to better outcomes when surgery is performed sooner. Surgeons have to balance these data points and manage it on a patient by patient basis.

At my age the curves cause irregular degenerative wear on the facet surfaces and the older I get, the bigger the curves and the harder it is to fuse or recover from surgery, so I understand why the literature points that way. The best I can do right now is to choose the most knowledgeable and conservative surgeon which I did. Dr. Bitan is the chief of Spine Surgery at Lenox Hill hospital in NYC, a renowned scoliosis specialist, and he believes he can start with laminotomy and discectomy, and when fusion becomes the best option, he'll look to try just an L4-S1 fusion before considering T12-S1 if possible.

I guess that even if they did have devices to help reduce the stress and wear on adjoining segments of a long fusion, the unique twists and curves of scoliosis would exclude us from being able to use them.

Thank you MDE for your time and assistance as I explore my options. I hope you and yours have a blessed Holiday Season and a Healthy New Year! Thanks Again!

[Genn]

the whole situation left me in a real conundrum.... i was told not to get a prodisc for several reasons (some unique to me; some not), and the nickel risk wasn't worth it to me. my insurance would have paid.... god knows what would have happened had there been problems w/ it down the road, b/c it's a royal mess to fix.

also have heard of the PE inlay coming out, esp in young women at L5/S1 - since it goes in as 3 pieces, 1 can always come out... the plastic part. forces at that level put a lot more wear and strain than at others.

there are case reports out of TBI of young women (like me) getting lymphocytic granulomas in their spines around older implants.

instead of incurring those risks - known, but none of which has a known/good "fix" -- i went with the more upside/uncertain downside approach. the truth on the M6 is that all we know is what we're told, and i hope that anyone w/ a negative experience would pipe up and say so, even in an anonymized fashion.

stenum is putting in how many hundreds a month? though i will say, i see fewer people complain about any outcome of an M6 than a Prodisc... but there is NO DATA... for better or for worse.

Doc, MDE~ This is exactly what has left me in a conundrum, as well. Although, I am looking at a Hybrid w/ ADR @ L4/L5. The thought of having a ProDisc implanted keeps me up all night- when I should finally be at peace with an operative decision! I am Not!

We are of the same age, etc. and, I have the same concerns listed above with addition to wanting to preserve my facet joints as much as possible, with an appropriate device.

Unfortunately, I've been unable to find much Current first-hand info on other implants (besides the M6).

I'm almost at the point where I'm willing to split this procedure into 2 parts- Have the L5/L6 fusion done here and possibly travel at a later date for the device implantation. Unfortunately, this may not be an option for me in the future if I wait.
My L5/L6 has completely collapsed in 2-3 years time of being bedridden and my degenerative facets, arthritis, etc at this level have been noted as 'rare' in the aggressive degenerative progression. My surgeon has mostly seen this with failed surgeries or discograms (infection in the disc). So, waiting to do the L4/L5 at a later date may very well remove me from being a ADR candidate at this level.

I hold great disdain towards my previous NS for making me wait this long. However, it is what it is now.. And, I have to deal with the 'Now'.

What to do with L4/L5? There must be more options...

Any advice or info would be greatly appreciated.

GG

[MDE]

I personally feel that there is a bit of skewed perception of results A) with ADRs in general, and B) with Prodisc.

When you look at the long term follow up studies that have been done, All ADRs show equivalence to fusion, and most show superiority. People hear of the worst of the worst ADRs and I think a lot of the original Charite and Prodisc issues are caused by surgeons who were still at the short side of the learning curve. I don't believe Charite is a great device personally, pro-disc is better, but I believe because these two were the first on the market, they show much higher failure rates because surgeons didn't know what they were doing. They've also been on the market longer which means there are thousands more implanted, and they've been implanted for 5-15 years longer. It's expected that there are more "bad experience" stories out there with these devices. The industry has learned a lot about UHMWPE (what the inlay is made of) and how to make it more wear resistant over the past 15 years (and the type/shape of wear particles that are created has changed as well.. it's amazing how detailed this gets)

The only true problem with Pro-disc is it's ability to be revised. The need for a revision is mostly determined by bone quality (to avoid subsidence issues) and surgeon skill. Bone density can be tested, and surgeon skill is comfort with the system. I would say any surgeon doing ~50 discs a year isn't going to run into problems. Unfortunately, not all of the new systems (including M6) really do anything about this problem either. (the ability to compress may reduce the likelihood of subsidence problems, but if it has to be revised you're still left with a difficult procedure) If you have those two things going for you, my gut instinct would place success rates at about ~95%. (this is purely speculation based on reading a lot of clinical literature.)

I always go back to my personal preference. I would rather have the "worst" designed device implanted in me by a surgeon who uses that device all the time and is very familiar with it's use (problems and how to avoid them etc) versus the best device implanted by a surgeon not familiar with it. On top of that, I'd seriously consider a two level fusion instead. Facet joints will take move abuse with a ADR than fusion because when it's fused, they're not loaded whatsoever.


Sorry for the delay, and I hope this puts your mind at ease a bit.

[ADRboy]

Greetings MDE,

I am in my late twenties and facing lumbar disc replacement. Scary!

I have been in contact with a Mr Boeree, and his website recommended this forum.

I have been reading about the M6 on internet forums and blogs, and I do have some concerns about it's durability.

I have read testing has been performed in the lab for 20 million cycles.

My question is how representative is this testing of the actual lifespan of the artificial disc? I have seen lots of debate about this, but no really informed answers! Is it an unknown?

In another ladies blog, who had an M6, she had mild scoliosis which had pushed the disc slightly to the side. She is fine though! I would've thought this extra load would put even more weight on the disc?

Love to hear your thoughts!

Regards,
Paul.

[MDE]

*Short version*
Mechanical testing is done in a way that controls as many variables as possible and evaluates how it may fail in a typical situation. Unfortunately, there are hundreds of other variables present in actually surgeries. Companies do not publish this data as rarely is the patient the one making the device decision, and they do not want their competitors to know test data values. Also, the 20 million cycles is not the life of the device, but I'll get into that more below.
*end short version*

The average person loads a disk approximately 1 million times per year. This is directly dependent on how active a person is, but 1-3 million cycles per year is the textbook value. Literature values range, so for completeness, another source states 85 million cycles = 40 years. 40 years is widely recognized as the goal for device lifespan.

Those 1 million cycles in a year have a varied load. Sometimes you're just walking (each step is 1 cycle) These are relatively low load cycles. So if you take 1 million steps in a year, how many are while carrying heavy loads or landing on your feet after a 4 foot drop etc. Those more extreme conditions would increase the force on the disc in that one (or more cycles).

Mechanical testing is done assuming that worst case scenario loading. Typically they use what has been found clinically to be the absolute maximum the vertebral bodies/discs will take (between 2-6kN of force typically) and repeat using that force for the entire fatigue testing, which would be XX million cycles at 6kN of force in compression.

So there is one other trick to keep in mind. For ADRs that are have bearing surfaces, you stop the test every million cycles to analyze the wear particles that have been generated. This includes the total mass of wear particles, composition, the shape of them, etc. This gives you 10 data points on wear particle generation through a 10 million cycle test which then gives you a pretty good data set that can be analyzed and extrapolated from. Basically, even though you only tested to 10 million cycles, you know how much and what kind of wear you would have at 85 million cycles.

For discs like the M6, it's not quite so easy. First of all the wear is not created from the load bearing surface and the wear isn't really the main concern. Realistically the biggest area of concern is the PE (annulus) to titanium bond strength which is something that data cannot be extrapolated from, it either fails or it doesn't. So there are two ways to "cause" a failure, load (increasing the force you're applying) or life (increasing the number of cycles).

I would really really hope (and expect that) the engineers responsible for the product would know how the device responds to both. They won't publish that type of information because a) device companies HATE releasing any sort of valuable test data to their competition, and b) most of the patients reading it wouldn't really understand what it was saying.

The wear that may be created (from PE on PE in the annulus) really comes from a large number of surfaces, that will all wear at different rates depending on the type of cycle. While still able to be extrapolated from, the type of wear created is less predictable and thus requires longer fatigue life testing to evaluate.

Unfortunately defining "a cycle" and how a worst case scenario cycle for a ball and socket style disc is different than a worst case scenario cycle for an M6 style disc is another long discussion. End point is that it's just another reason why it's difficult to compare testing of different designs. Needless to say, each company has their own test methods and while industry works with ASTM to create testing standards, many times the worst case test for devices will be different.

There is a book: http://www.amazon.com/Motion-Preserv.../dp/1416039945 That has a lot of good information, however it isn't completely unbiased as the authors have some financial ties with specific devices. It's also expensive.