Grand Rounds-A Hybrid Minimally Invasive Posterior Interbody Fusion Technique

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- Hello, ladies and gentlemen, and thank you for joining another session of the Grand Rounds. Tonight, we have two special guests, Dr. Charlie Branch and Dr. Joe Chang, none of who require any introduction to going to talk to us about cutting edge minimally, invasive spinal procedures. Charlie, Joe, thanks again. And please take it away. Sure. Thanks Aaron. It's a pleasure to help moderate this session and introduce Dr. Charlie Branch who's Professor and Chair of Neurosurgery at Wake Forest University. I also wanna say thanks to Anneliese Rodriguez, who is currently a resident of Wake Forest and who helped put all this together for tonight's session. Charlie, why don't you get us started and talk to us about this new minimally invasive technique that's actually starting to pick up a lot of steam.

- Thank you, Joe. It's a privilege to be here with you. And again, my thanks to Anneliese, she's tied up doing clinical work, otherwise she'd be here with us this evening as well. The minimally invasive world obviously is kind of, it's a hot topic. I think the challenge we all have is, what is minimally invasive spine surgery? I think everybody has a different perspective, there's percutaneous, endoscopic, tubular retractor, we've got expandable retractors now, they're muscle splitting, muscle preserving navigation from the side, from the back, from the front, a lot of different sort of thoughts. But really would like this evening for us to focus on really what our goals are. Contemporary spine surgery should minimize tissue disruption, maximize the therapeutic benefit, minimize radiation exposure, minimize blood loss, and really be an efficient consumer of OR time and resources, and even hospital resources. And I think even most important is, we've got to be able to optimize the learning curve for a new technique or technology, so that as old guys, or those of us who've been in practice and learned it a certain way, can develop a skill quickly that gives us access to this, a minimally invasive or less invasive approach. And so this evening, I'd like to introduce you to, or familiarize with you a technique that uses a very familiar approach, a midline laminectomy type approach that allows us to do a direct decompression, remove bone ligament, hypertrophic facet, and get the nerves and duro decompressed and even do an interbody fusion, either unilateral TLIF or the bilateral PLIF approach. And then, with the novelty being, instead of exposing out over the pedicles and pulling down muscle or using navigation or other techniques to put in percutaneous pedicle screws, we're going to actually take advantage anatomy already exposed to put a cortical bone screw fixation that really doesn't require any more dissection than we've already done to duro decompression. We're gonna call this as hybrid or mini open midline, lumbar interbody fusion approach. Does that gets your attention, Joe?

- Yeah, it does, I think it's actually a little bit more my opinion than just another minimally invasive technique. I think it's another tool and , and I hope to kinda go over some of the anatomy pores, because one of the things about this technique is that it's a little bit more medial. And so for example, if you're doing a pedicle subtraction osteotomy, you have to close it down with a separate short segment of fixation. And you won't have room for the longer rod next to it, with a traditional technique. And I think migrating that heads a little bit medial may allow you a little bit better ability to put both rods next to each other. So, what do you think about, can you tell us a little bit more about the anatomy on that and the starting trajectories?

- Yeah, let me sort of show you. I think, as much as we like to think this is a new, something new, in reality, and Art Steffee, years ago, one of our great champions of spinal surgery and fixation surgery really coined the term force nucleus when he identified this really, this juncture confluence of the superior facet, the pars lamina, and the pedicle, transverse process, a lot of intersecting forces on this place. So this bone arguably is the most durable or the most stress resistant. And, and in fact, if we can use a bone fixation technique that engages this bone, we're probably purchasing the strongest bone in the segment. And, the entry point or this approach is pretty consistent even with the degenerated spine. The transverse process lamina pars junction is a reproducible element, even with pretty pronounced degeneration. And by using this junction, the surface anatomy can now come a few millimeters medial and begin a trajectory that goes across the force nucleus or cortical trajectory in the bone, we've actually used a surface anatomy that didn't engage or disrupt the adjacent facet and purchase some of the strongest bone in this segment. So that really argues, would I rather come out here and the dissect muscle off or come percutaneously and put big pedicle screws in, or with an exposure that's already done to do a decompression, can I get the segmental fixation and potentially have a better of a more durable bone fixation and get the benefits of less muscle retraction, blood loss, get the rods closer to this axis of rotation and reduce some of the surgical exposure closure times? So I think there's some real benefits, this is not just another gimmick, does that make sense to you?

- It does, and I think a lot of the purchase of the screw into the cortical bone actually would probably allow some pretty good biomechanical strength of that fixation. And it looks like you were about to tell us a little bit more about that.

- In fact, one of the neat, not neat, this study, actually, this is almost seven or eight years old now. The study was done back in '07 and it was published here in the Spine Journal in 2008. Where we took some cadavers and I've got to give credit to Rick Hynes and Santoni, I mean, they really did the work along with the rest of the team and said, is this cortical bone technique, is it valid or are we actually sort of maybe putting a smaller screw in good bone, but not getting good fixation? What they did was they compared traditional screws, 6.5 millimeters X 50 millimeters screws, placed through the traditional pedicle approach with a cortical strip. And this isn't just a big, this is a 4.5 millimeter screw that's only 30 millimeters in length. You'd think, wait a second. That's way too small. But, as you're gonna see here in this cadaver study, these small screws placed through the cortical trajectory, actually had greater resistance to pull out, almost statistically significant resistant difference. And as we look across this continuum, these screws generally are in the dense, the more dense bone, the Hounsfield units of the bone on the CT are much greater or denser. So, we're actually purchasing dense bone. And this is really important when we get to these osteopenic or osteoporotic patients, which are pretty common in our aging population. So yes, we could get a large screw that goes way down deep into this bone, but it's really not good bone. And in fact, as we discovered in this study, these small screws in more dense bone actually had greater pullout resistance. This particular study showed, as you saw, greater resistance to pull out with these smaller screws. Why? Well, let me show you this sort of model. This is like a cutaway that I think helps illustrate the point. And let's assume this bone really is osteopenic. In this pedicle screw, for me to really get great resistance to pull out, I've gotta have a perfectly-matched screw to the size of that pedicle. And even then, only maybe 20 or 30% of the screw is purchasing cortical bone. Whereas in this cortical trajectory, even with a smaller screw, 60, 70, maybe 80% of the screw itself is now purchasing cortical bone even in an osteopenic patient. What do you think of that?

- I think it makes a lot of sense, certainly in patients with osteoporosis and osteopenia, we know that the bone actually ends up towards the margins at the cortical surface. And so, it makes a lot of sense that you'd probably get a lot better purchase of that. How do you avoid fractures of that area? Is there a technique that you use to not fracture the cortex as you're drilling through that?

- And that's great, I mean, one of the challenges I always had with these osteopenic folks was really matching that pedicle screw to the pedicle without kind of cracking it. It's amazing how dense this bone is here, but as with anybody who's done carpentry knows that if you oversize a screw in hard wood or drill too small a hole and don't tap it, you can actually crack even pretty hard wood, and certainly this is true with bone. So I think it's really important, and we'll focus on this a little later, that as we drill our pilot hole, we drill a pilot hole that's 30 millimeters deep. We tap the hole with the exact same size threads that, of the screw that we're gonna put in. We use the term line to line so that the diameter of the tap and the depth of the hole are the exact same as the screw that we're gonna put in. That's a little different from those of us that have, I think probably under tapped our pedicle screws, and oversize the screw a little bit so we've got a good snug purchased right here at that point. Let me show you the technique, kind of quickly go through that again, here is a very familiar midline approach when using a midline incision and leaving the interspinous ligament and dissecting the paraspinous muscles away from the lamina. And as spinous process, one of the tools I've been able to use is this sort of almost a speculum that lets me kind of use the blade-like periosteal and then rotate this thing 90 degrees and open it, almost like I was doing a pituitary case for those of you pituitary guys that are watching. But again, we open this, the speculum and that lets me slide this retractor right down along the bone, without really disrupting any more muscle than I have to, then it gives me a minimally invasive concept. And then, after quickly getting both of these in, now I've got this great exposure with very limited muscle dissection. As opposed to these table mounted retractors that are fixed in place, this actually lets me rotate if I need to, very similar to that shadow line retractor we use for anterior cervical discectomy infusions. I think the unique thing about the retractor that we've developed for the Medtronic system was that, actually this retractor rotates on an axle so that once I've got it in place, I can actually now rotate the blades and hold them in position. I'll show you a little bit of that in the video. Probably more important is, at this point, because of this relatively unique, but reproducible anatomy, I can now drill a pilot hole in the cortical bone, either before or after I do a decompression. Some people really are a little bit nervous about putting a drill down here once you've done a decompression. Personally, I like to go ahead and get my decompression done, whether it's the TLIF or unilateral or bilateral approach and see my dura, I can actually feel my pedicle. And then I quickly drill my pilot hole across that cortical trajectory and no more dissection. You'll see that again as I illustrate this with my video, kind of go through a few more steps, but this is the key one. And I think, spend a little extra time here. Because all of us that have done pedicle screw fixation for all these years know that you enter the pedicle out here just at that lateral sort of edge of the superior facet, trying not to encroach on the facet joint. And then a trajectory for my tap or my screw is parallel with that end plate, right along the track of that pedicle. I'm going from lateral to medial, following the trajectory of the pedicle. Well, the cortical technique turns that on its head, we're gonna go instead of parallel with the end plate, we're going from caudal to cephalad starting just at that junction of the transverse process and pars, which on the lateral view is right at the upper margin of the framing, and then aim up toward that apophyseal ring of the vertebra. And then we're also gonna go from medial to lateral. You can see it illustrated here. So as I drill my pilot hole, I'll lean it up against the spinous process and aim out. Again, across the pedicle into that hard apophyseal ring. So it's truly a bi-cortical purchase if think about it in some ways. I'm gonna show this again, a little bit more detail as we move forward. This anatomy we never see in the operating room, but we're gonna see it here. It reminds us again, this junction of the transverse processing pars is right at the upper margin of the foramen. You move in about three or four millimeters, pilot hole trajectory that goes across the pedicle into that apophyseal ring out here. Again, once we get comfortable, and I'll tell you, the first few times you do it, you're uncomfortable, but after that, it's a very familiar approach. Share your thoughts, have you done one of these this way, or have you any other tips you wanna share with our audience, Joe?

- Well, actually, no, I haven't done certainly as many as you, but I've certainly have tried this technique, this kind of superior lateral technique. Well, one of the things I was gonna ask you to share with us is, what tips would you give to the surgeon who's just trying this? 'Cause it's totally different. 'Cause you're not feeling the cancellous bone in the pedicle with your gear shift, you're kind of marching down that path of least resistance like we typically are used to, this is almost like a pure trajectory using a drill and then, just really not plunging past the cortical bone.

- And in fact, again, those of you that have done a high-speed drill either for a craniotomy or any bone work, you know that if you take a very fine tip drill and turn it on full speed, you can actually palpate your way through the bone. And if you're sort of bouncing your way to the bone, you feel bone all the way through. And one of the, I think the comfort zones of this is as you're bouncing, if I can use the term and anything, and if you can almost see my hand, if I can bounce my drill through the bone, then I'm very, very confident that I've got a hard floor all the way down to the depth of 20 or 30 millimeters. You'll see, here again, leaning the drill up against the spinous process almost gives you that perfect medial to lateral trajectory. So those are a couple of tips and I'll show you some more as we get through the video. This is a great view because it reminds me, again, I'm never gonna see this view on my intra-operative fluoro, I might on a navigated system. And for those of you that have image navigation, it's a great tool to use with this technique, it makes it almost just too easy, I shouldn't that. But certainly, with AP fluoro, when you start three or four millimeters medial to that pars, which is about five o'clock on this pedicle, and aim for 11 o'clock, perfect trajectory, or seven o'clock to one o'clock on the contralateral side. And then, again, I've gotten to where I almost never use the AP anymore, I've done enough of these, but on the lateral view, if your entry point is at the upper margin of the foramen and you're aiming up, then it's the safest trajectory you can have. So, these are some sort of tips. And again, this video is gonna be a nice reference for those of you that wanna use it as you do your first case or two. A couple of points illustrated, you see this drill, you start, we sort of drill that target right there at the upper end of the foramen, drop the drill down so that it's aiming up toward the apophyseal ring, lean it against the spinous process. So we're going from medial to lateral. And it's almost like the existing anatomy is directing you in the right direction. A little tip here, you'll see on this illustration that it's almost that one of those tiny matchsticks. I actually use that sort of fluted shaft drill that we use for craniotomies, the side cutting blade for the craniotomy. I think, what you'll find is that actually cuts a nice cleaner whole all this with and does a good job. More important, and what's not shown on this, is that the exposed head of the drill has to be 25 or 30 millimeters long. So you can get that drill trajectory that's at least, or the pilot hole that's 25 or 30 millimeters deep. And then a tap that goes 25 or 30 millimeters, whatever length screw you're gonna use, I almost uniformly use 30 millimeter screws. My sort of standard is a five millimeter by 30 millimeter screw. And it's amazing how you can use that almost every time as opposed to having to go to a 5-5 screw or 6-5 screw or 6-5 screw, almost makes it more standard, and then this is what it would look like when we get done. Again, a different look, but a very effective fixation. So, which do you prefer? Are you a TLIF guy, Joe? I didn't know, this is a great nomenclature. Some people, unilateral facet removal and interbody fusion, or are you PLIF guy where we actually take off both the facets and do bilaterals? Either way, this, as you can see here is a great fixation through the exact same exposure that you've achieved for your decompression infusion. PLIF or TLIF? What do you think.

- Personally, I've stopped doing PLIFs, so everything I do now is a TLIF. Maybe I'm just getting lazy, I only wanna do 1/2 the work going into the interspace.

- Well, it's actually 1/2 the cost as well, or not 1/2 the cost, it certainly reduces costs. And this is a challenge that we're gonna deal with. When we talk about cost, we don't think about radiation exposure, but I'm gonna have to take this point to remind everybody that this technique, as opposed to a percutaneous fluoroscopic guided technique, where, yes, we can get perfect pedicle screw placement with 2 1/2 minutes of C-arm fluoro time, I think the real cost of radiation exposure may not be appreciated. I have to tell you that I can do this procedure with about six seconds of C-arm fluoro time. And I think a very worthy or reminder that the cost is not just money, and through a little bit opening. Can I show you a video of how I've done this? And I've kind of taken a video and cut it down to about six or seven minutes that I think gives the pertinent points.

- Absolutely. How long does it take you to do this procedure, does it the same amount of time as it used to when you did the standard pedicle screw fixation and post ?

- It's actually less because I don't have to do all that extra dissection. So now I'm making my, one of the beauties of the minimally invasive is you sort of direct it right to the spot, dissect just enough tissue to get this done. And so if I don't have a ultra heavy patient with recurrent disc in scar, this is a 1 1/2 hour operation, or hour and 15 minute operation, almost routinely. So it's not an excessive timeframe. Let me show you this, this is a patient that I actually did, actually a couple of years ago now, let me start the video player. And, he's 60 year old he's got neurogenic claudication, you'll see here, he's got a fairly straightforward, single level stenosis at 3-4 with a degenerative slip, collapses even worse when he goes up right. So I think this one even got through my insurance company, Joe, without too much fuss. So it was a pretty straightforward case.

- Yes.

- Yeah, Well, that's the deal. Midline incision about 4 1/2 centimeters at length, I dissect my soft tissue away. And what's interesting, I think I know people can appreciate it, I'll stop for a second. With this speculum, I can see exactly, this is actually an eight centimeter mark. So this guy had a bigger back than, it wasn't skinny mini, right? So this is an eight centimeter deep hole that I've actually dissected the muscle away from the spinous process and lamina, and can insert my blades without too much extra fuss, open the blades up, I'll rotate them, so that they actually, the blades flange out at the bottom. And if necessary or you like that, you can go intra tubular light sources you can put in, adds a little cost, but it certainly adds a light at the bottom. Personally, what I'm doing is I'm using a microscope. So, once I've gotten this exposure, I'll bring in the microscope, my resident can see and help. But, our nursing team can see and help, everybody loves this because everybody gets to watch the case. And, as you can see here, I'm using an osteotome to amputate the inferior facet of 3. And then I'll complete that facetectomy with a 45, we'll go across the other side, amputate the facet. So very quickly, I've gotten a majority of my decompression done. And then I'm gonna take my 45 degree Kerrison Punch or drill, whatever you prefer and remove, facet, and I really get a good decompression. At this point, I'll take my 45 or angled curate and identify the shoulder of the pedicle. This is the key landmark, and I think this is true of any spine surgery, this shoulder of the pedicle tells you where the edge of the dura is where the foramen is. And once you've identified that quickly, off goes that superior facet. And if it's a TLIF or unilateral, out you can, get that done, angle your scope, get your central decompression done. And you can even angle with this retractor, you can angle and get the contralateral side decompressed if you need to. And then as you see here, there's no retraction on the dura when the size of the annulus of the disc and dura really pretty familiar, right? The discectomy, any interbody fusion technique mandates good in plate preparation. So, this is a rectangular ring curette that I'll put in here and rotate around and you'll see, I can deliver a lot of this pretty quickly, I'm impatient so I gotta get this done quick. And so, but we've got to get it done well. So this reverse curette really gets in plate preparation, I just can't stress that enough. TLIF, PLIF, doesn't matter what you do, DLIF, XLIF, YLIF, ZLIF, you gotta do good in plate preparation. And spend a little time cleaning that out because ultimately that's gonna determine your fusion rate. And then getting the right size grip. I'm gonna stop here for a second. You may remember, Joe, this guy started with a totally collapsed disc base and actually had a loose thesis. And now I've actually been able to restore his disc base to the same height as his 4-5 level. And so I'm gonna get a 12 millimeter interbody spacer because this is a 12 millimeter high device. I think, be real careful not to put in two small an interbody spacer, or you end up basically just promoting motion or maybe even worse, not getting the lordosis that you need. So, a tall spacer, way up front or a lordotic spacer is something I think we're coming more and more aware of the value of you. You see that lateral fluoro lets me really kind of get a sense of that I've got this in, I've restored the height, I've restored the alignment. And now I can quickly go to the other side, I've got a funnel here that's full of that bone that I took off, grounded up, I'll pack it in. So I've got 15 CCs of bone in the disc space. Again, this is not about doing a PLIF as much as it is about cortical screws, but you can see how quickly I can even get bilateral interbody spacers in and get a good symmetrical height restoration, foraminal decompression, all the things you get from interbody fusion. Good bone graft interface, but most important, look at that realignment of the spine. So, now it's time to put in our fixation, okay? We've done our disc decompression. We've done our interbody fusion. And rather than now, bringing in the C-arm or the O-arm or the, starting a percutaneous pedicle screw fixation with a lot of radiation or dissecting further out with a little more blood loss. I said, okay, I'm gonna pick my trajectories, remind myself of that, and, where do we go? The same view that I've just had, I'm gonna feel my pars, you see, I felt over the edge of the pars, came in four millimeters, drill the pilot hole, angle that drill so that it's actually aiming up, where you say I'm bouncing through that. Remember I was telling you about bouncing, you sort of feel your way through the bone and just bounce through the bone. Get that 30 millimeter exposed side cutting drill bit. Now I can palpate and make sure that I've got a good bone tube, use my tap. And remember that seven o'clock to one o'clock, and you wanna screw that, sort of ends up right out here. So it's traversing the trajectory of the pedicle. And now in goes to the screw, this is a five millimeter by 30 millimeters crew. It's important as you're putting these in, once you get about halfway down to release the shaft of the two holding in the screw, because what you wanna make sure is that, that head of the screw is very loose because as you get to the bottom, as it tilts a little bit, that's when you stop putting this in. Now, you see what I did? I just angled the scope, just a millimeter or just a degree or two, not look across the other the side, matched my trajectory with my existing screw and I've drilled my second hole. No more dissection, I mean, that's what's almost, it's pretty attractive about this because very quickly I've got four screws in with no bleeding, no dissection, no radiation, other than a couple of shots on my C-arm. So I've got those two screws in, now here's my decompression, here's my PLIF, Here's my edge and my dura, here's my superior, sort of facet surface and pedicle. So I'm gonna try to come down to the bottom of that facet. And of course, as you see here, I'm at the right spot, but I didn't lean my drill down against the opening, right? And so instead of coming up at an angle, this ended up going straight out. Good news is, it's still a cross cortical bone, cortical bone, medially, cortical bone laterally. And, in goes the screw, and then a second screw on the opposite side. So, as you can see from the video, I haven't really edited out a lot of steps, this is pretty much real time. So in the five minutes or so that we've been watching, we've actually put in all four screws with no additional bleeding and no additional dissection. And I think that's probably the most attractive or minimally invasive element of this is that, we've ottered the tissue and the time and the radiation. And then very quickly, once the screws are in, we align them, a three centimeter, a 3 1/2 centimeter rod is now seeded onto the screws, locked in position. And the rest of it's just like you do a pedicle screw rod fixation. What are your thoughts on this there, Joe, is this, I sort of picked up all the high spots?

- Yeah, I think so. I think some of the things that I think our viewers may wanna know is what levels can you really do this, Charlie, is this just for the lumbar spine? How are up in the thoracic can you go.

- Well, I've gone up into the lower thoracic spine. I mean, I've basically done, started doing the deformity correction cases with these, I haven't corrected the deformity with them. I've actually corrected the deformity with the PLIF and then use these as a fixation. The further up you go in the spine, and I'll stop and I'll back this up just a minute and show you that picture. The further up you go in the spine, the more the narrower the pedicles become. And therefore you can actually, while the pedicles down here at maybe four and five or round, or really oval, the further up you get, you notice how kinda thin these pedicles are slender. So, you're gonna have a more vertical trajectory, almost a 6-30 to 12-30, whatever you're gonna call it, a trajectory or even more straight up than that. And, so I've gotten up into the T10 level now. Again, that's my anecdotal experience, and I think everybody's gonna get to pick up their own. But, more and more folks are finding that this really great, it's a great fixation for older patients who even have multi-level fusions with osteopenic bone, just reduces the dissection. And then as you say, from a minimally-invasive single level approach, out comes this retractor, these retractor blades are two centimeters in width. And I've got enough of an incision so I could get what I've got done. And, it looks like we just got started, I'll reapproximate the stash to the spinous process and interspinous ligament, and then kind of away we go. So, I think it qualifies as minimally invasive, certainly we're gonna call it hybrid, mini open, minimally invasive hybrid, whatever. I kid with my colleagues, would you rather have four or five or six little poke holes on your back or one nice little neat incision? But that's a game we all play, isn't it? The goal really is to get this guy fixed and getting decompressed and stabilized. So, that's the technique. As I promised I would, kind of get through that video and let's see if I can share a few cases with you over the next 10 minutes or so. And, let's sort of look at some practical applications, that work for you?

- I think that's a great idea. See how this works in a real world.

- So, here's an interesting case. This is another 3-4 case. This actually is unique because this poor lady had a microdiscectomy six months earlier at another hospital. She presented with a L3-4 disc herniation, straightforward discrimination. But, very quickly, about two weeks after her surgery, she had a dramatic recurrence of her symptoms, tried non-operative therapy, ultimately had an MRI imaging and was found to have a huge recurrent disc herniation. Well, when that happens in my book, I'm more as why did that happen so quick, right? Turns out she actually had a lytic spondylolisthesis that was unrecognized at the level of her disc herniation, let me show you that, kind of a wonderful sort of, oh my moment. Here's her preoperative picture, nice little dicentric disc fragment, unresponsive to non-surgical therapy. Had her microdiscectomy at the correct level with a nice little hemilaminotomy even preserve part of the facet, and now look at that massive recurrence, just a few weeks after her initial treatment, what on earth happened? Well, let me show you here. Unfortunately, she had a lytic pars defect here at this L3 level, and when we got plain x-rays on her, she had a slip, it was bilateral, so it wasn't iatrogenic, it was just an unrecognized sort of bad luck thing, I guess. But, this is not a case that you're gonna go just do a recurrent discectomy on. I believe, even you would agree this one needs to be fused, is that right Mr. insurance doc?

- I totally agree with you on that.

- And it's amazing what we have to kind of rationalize to some of our carriers now, but I think this one qualifies. And so, and it's a reminder sometimes that even on our straightforward microdiscectomies for this, that just the value of plain x-ray, just an AP and lateral standing film sometimes will give you a good clue about what else might be going on. And you can see she really slips. So, to me, this was a great case to go back in through her previous microdiscectomy incision and make the same little incision, do a nice generous laminectomy or a hemi laminectomy decompression, restore the height, get her interbody fusion done. And with these cortical screws, as you can see, going from medial to lateral, medial to lateral, great segmental fixation through the microdiscectomy incision.

- How long was she in the hospital for, Charlie?

- A couple of days. She was hurting and so she was a large lady. I think you'd get a sense of her size. But most of my patients with this approach go home after one night and occasionally, two nights in the hospital. But most of them are over nighters and then home the next day. So, it really, it almost makes it tough for me when I'm deciding, especially the degenerative spondylolisthesis group where we're trying to decide, should I just do a decompression or should I do a decompression and infusion? That group is just sort of that one-ish, because now I can do the same incision with the same sort of relatively limited morbidity, I can actually do the fusion. So it almost makes it harder not to, sort of created a problem for myself. Here's another case, everybody's asked me, well, what if they got a pars defect down at the L5-S1 and you've got to do like a Gill or take off the floating lamina, can you still use the cortical trajectory because of the missing part of the lamina? Here's a gun, 5-1 standard sort of tried everything but didn't work. He has a 1-2, probably on the verge of a Grade 2, lytic spondylolisthesis, pretty significant kind of, unroofing of the disc out into the bilaterally. And this is the great, oh my goodness! This poor 5 root on both of these, is a sort of a tough, it's a tough one because, that fluoro 5 roots pounded on both of these. And so, what are we gonna do? I think the goal here is, 'cause we wanna do what we would wanna do. We wanna restore the height, open up the foramen, get it decompressed, in this case, I actually left this guy's lamina in the center so I can sew it back, but you can see, I got a great height restoration. And, in this case, again, I used a little longer screw and I'm showing this to kind of remind everybody, but because this is sitting out in the apophyseal ring, as you can see here, it's not actually in the end plate and I'm not encroaching on the end plate at the level above. And we all know that when you got this pars defect, you have a pretty limited opening for bone. And in fact, if you try to put a pedicle screw in here, often that ends up cracking the par. So, this is a great technique, and if I was gonna do this again, I'd put a 25 millimeter screw in instead of a 30, just sew tips of the trade. Another thing I'll sort of talk about is the S1, you'll notice that these S1 screws are actually pedicle screws, these are 7.5 X 35 millimeter screws. Once I've gotten this S1 pedicle exposed to do my PLIF, rather than trying to put some screw out into the ala or some funky angle, I can put a screw right down that pedicle, aim it at the promontory or close to the promontory like I normally would, and then, bingo, I've got effectively a pedicle screw. And so, it's a neat, I guess, approach to getting this done. We'll let's see here's another, what's this one here? This is somebody who actually had the same problem, but had a pretty profound degeneration at forethought. And so through this same approach, I was able to actually use my lordotic, my graft device and get a two level done as well. And if you go back up to the skin, you realize that the skin incision kinda gives you a trajectory that gets both. So the TLIF here at 4-5, and the bilateral PLIFS at 5-1 to restore height and lordosis, and really get this done with the cortical trajectory. Again, I think it gives me a good sort of fixation technique. Any thoughts? I'm just curious, I mean, what do you think about that? Is it something that makes you nervous or is it something that's worth thinking about?

- Well, that's, I think it's a good technique. Speaking of nervous, I mean, is there any pitfalls that you would consider, like, for example, if you put in too long of a screws on your other case, with the screw tips look like they're in this space, they're really not because they're a lateral to the disc space by now, in the cortical area. Any, suggestions for how to avoid putting in screws, say, for example, let's say you get out into the solus and with the plexity, any words of wisdom related to avoiding complications and problems with this?

- I think, honestly, as you get more experience with it, you come to realize that shorter is better. I hate to say that, but it's actually true. And so that the shorter screws are very effective, and a 25 or 30 millimeter screw that's sort of sitting out. And when you get a model, you realize it's actually a pretty innocuous space out here. And another thing that I think it's important to know is, if when you're putting in this screw, you happen to actually crack the lateral pedicle or whatever, okay? Tilt your retractor little further out and put in a conventional pedicle screws. So you can actually rescue, one of these, if you've actually sort of drilled a little too lateral and kind of cracked the lateral wall, and you're unhappy, well, then put in a conditional pedicle screw. Conversely, if you've got a pedicle screw in place that you crack the lateral wall with a pedicle screw, you can come and put a cortical trajectory across and actually rescue your fractured pedicle with a cortical screw. So, it's a great rescue technique, if you happen to need that. Let me show you a couple more cases, and then, we'll try to wrap this up since we're getting up on, here's, again, can you do this in a two level? I hear somebody who's actually got the synovial cyst and unfortunately got, stenosis not only at the 4-5 level, but actually laterally at 5-1 as well. We sort of, we see these and, you then wonder, oh goodness! Should I just fuse 4-5? Should I not fuse either one? What's the right thing to do? Well, you get flex and extension films, and sure enough, there's about a seven millimeter slip at that level and this one, so this is somebody who had kind of gone down the trail for several years, and this was a great option for me. So through the small incision, we're able to get both levels done, the height restored, maintain the lordosis. Again, small screws, rather than big screws. If in fact you get one of these, I'll warn you, this'll be my last case, kinda tip and trick. This guy as you'll see here has got a collapsed 5-1 that looked pretty good, I thought, should I fuse 5-1? Do I need to do a preop? This one's got a degen-spondy that was slipping. So, I had to fuse 4-5, and then, how about an inside 2 fusion of 5-1, right? This is the tight level, somehow or another is my little red dot's not working, but that's okay. You can see up here, this is the tight level 5-1, looks okay. So I go by and there we go. And so, what did I do? Got a good cortical bone screw, super-duper PLIF here at 4-5, and I went in and just put some screws in here at 5-1 thinking, okay, I'm just gonna put screws out into the ala of the sacrum and kind of lock 'em down, right? Well, the problem is he was just miserable postop so that gave me a chance to get some x-rays. Well, again, I got pretty good in plate preparation here. A lot of good grab, maybe kind of carved into the superior end plate of fives, I got to critique myself on this, but I got a lot of good grab that was good. Most important though, was here at the frame and at 5-1, locking him down like that without doing a good decompression, that superior facet was nailing that 5 route, and he was just not a happy camper. And, by the way, if you just don't get a really good alar trajectory and you put a screw that you think is adequate, look how close that poor screw is to the 5 root over here. So just a reminder that you'll see some published procedures that say put an alar screw in. I think in my experience it's been a lot safer just to kind of take that straight on down in a pretty vertical trajectory, put in a 30-35 screws and avoid that L5 root. If this baby had been any longer, we've been right on top of that 5 root. So, you learn from other people's mistakes hopefully. And so, I revised him, put the screws in straight, jacked this base up, opened up the frame, and now the guy loves me again, and we all go home happy. So hope this has been a good sort of, 45 minutes of midline exposure decompression with the critical trajectory technique. And I appreciate you, and sort of let me share this with you, Joe, and I'd love to hear your comments as we close our session this evening.

- Charlie, thanks again for the great job and for sharing this technique. But as you noted, this really is not a new technique, this technique's been around for quite sometime. However, I think what you've done is really helped us understand that there are some new tools that really allow us to do this. That's a really another good technique that we should all have in our armamentarium as we take care of patients and give them options for surgery. I think one of the other videos that we will be putting together is how to use this technique for spinal deformity. And I think those who are watching this video will definitely wanna check out that video as well. Again, thanks again, Charlie. And, thanks for showing us this technique.

- Thanks, Joe. Good night.

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