Tuesday, August 10, 2010
Nation: Question for our Readers
Recently, an anonymous source wrote TSB and asked that we pose the following question; "has anyone in TSB Nation (doctors are you listening) heard any complaints regarding a high incidence of peroneal neuralgia's following a 1-level fusion utilizing the StaXX cage in conjunction with an ISPD? It seems that there have been reports of patient complaining of a burning sensation on the foot and lower leg. Could the possibility be that the nerve-root is being overstretched? TSB wants to know what our readers have heard. You know what Linda Richman of Coffee Talk use to say; "Talk amongst yourselves." Or you can call in on 555-4444.
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No. Regardless of how much disc space distraction is attempted the annulular wall is the limiting factor in the anterior column. Think about the same force ocuring during flexion. The radicular symtoms can only come from something mechanically or chemically directly effecting the nerve.
ReplyDeleteRegards-The Professor
Professor - Are you saying that it is not possible to over distract because of the annular wall? If I remember correctly over distraction was a problem during the cage rage and can cause radicular symptoms at adjacent levels. Although the much of the annulus is removed in ALIF's and TDR's and it is well known that over stuffing can be a problem for adjacent levels. The StaXX device definitely has a mechanical advantage over the annulus, much like the tangs for the cylindrical cages did, coupled with an ISPD that may have been too large and stuffed posteriorly can definitely cause problems at adjacent levels.
ReplyDeleteLike most "professors" you are an idiot. Where do I start... too little time to comment further
ReplyDeleteAnonymous-thought we were having a discussion, leave what sales and marketing taught you at the door. Discussions amongst gentlemen seldom include the word idiot, in most circles.
ReplyDeletePlease expain, if you are willing and in medical terminology, how distraction of the disc space at a motion segment in the anterior column can cause unilateral radiculopathy at that level.
flhr- please site the literature on this. As I recall a majority of the cage problems (when used properly) were related to endplate distruction during reaming and nerve root irritation,at that level, when used for PLIFs (over retraction of the proximal nerve root).
The stretching of the nerve root (from retraction) results in temporary "foot drop"=medical term neuropraxis.
This is in all probability what is taking place- it is independent to what is going on in the disc space (surgical technique). Transverse stretching rather then axial.
The Professor
Professor - you are correct that subsidence and excessive nerve root retraction were a huge problem. Subsidence was particularly a problem without ped screws. I did a quick search, without wasting to much time, and found only one article which states we are both correct: Wetzel, F. T., LaRocca, H.. The failed posterior lumbar interbody fusion. Spine, 16: 839-845. 1991. Most of the over distraction came from the anterior procedures as I mentioned above. I am still standing by my opinion that jacking open the interspace with a car jack like the StaXX, even though it is slightly lordotic, has a huge mechanical advantage over the annulus. Keep in mind the reason that you are removing the disc at this particular level is because it is diseased. Does everybody do a discogram on every disc they operate on to see where and if the have any lesions anteriorly or laterally or posteriorly. I don't think so. If you add an ISPD to this it will make subsidence of the StaXX very difficult and hence the possibility for a radiculopathy at an adjacent level due to over distraction. In fact, I believe it is being used off label for an interbody in the US so there is not a proven technique for this device as an interbody. As stated on teir website: "The StaXx® XD Expandable Device is indicated for use as a Vertebral Body Replacement device inside the U.S." If SpineWave has that data and isn't trying to obtain approval for an interbody to relieve their customers from any liability by giving them instruction on the safest way to use the device in the interspace instead of using it off label that is a shame. If they are instructing the surgeon on how to use it off label ,oops I'm sure not. I don't know why anybody would use it when considering the liability and how many VBR's have been approved as interbodies. The risk isn't worth "wow this is cool!". Seriously, when is 1 more mm too much, just right or too little or maybe it is not 1 but 2mm or 3mm. MO industry needs to relieving their customers of liability when possible. Regards
ReplyDeleteGreat comments. Thanks for the feedback!
ReplyDeleteflhr: I believe one of the major barriers to getting the StaXx approved as an interbody is that it cannot contain graft. While it is only rarely noted, but the official device description would be: "intervertebral fusion device with bone graft, lumbar"
ReplyDeleteWhile not proof, if you look at LDR's ROI it is still classified as a VBR ( perhaps because it can't actually "contain" bone graft) whereas all their other enclosed IBFs have been reclassified as such.
Then why use it in the interspace? What is the indication for the StaXX in the interspace?
ReplyDeleteJust an FYI. Cages (interboby devices) were downclassified a couple of years ago allowing for approval via 510(k). The approval has nothing to do with whether or not you can put bone inside. They all need something inside. It is really just different astm biomechanical tests, etc. Given how difficult the FDA is these days, some companies may have just decided to continue to market as a VBR.
ReplyDeleteflhr: "why" is a good question--I presume the surgeons are using it as a nerve/lamina sparing device and filling around the implant with autograft. As far as I know all current interbody uses are off label in the US. http://www.spinewave.com/products/xd.html
ReplyDelete@10:49: my point exactly--they all "need something inside" but apparently VBRs don't otherwise the StaXx never would have been approved as one. Personally I think the LDR example is suspicious enough for me to assert that bone graft containment in-situ is a requirement for any implant with the product code MAX (IBFs).
Is the StaXs cage considered a defective medical implant?
ReplyDelete