I'm Frank Lamarck with the University of Michigan. We don't have many opportunities. A lot of you guys here teach a lot of courses and you're pretty fortunate to have together such an elite group of people in one place to go over such fundamental and essential points of knowledge that you guys should know and have to know before you graduate. But fixation techniques of the cervical-thoracic junction are not talked about that often because as you know or may not know, cervical scolateral mass screws are off-label. So we can't really talk about them in a non-CME setting and these are opportunities where we do get to go over these things and it's something we use very often. So when you get a chance to go over the techniques, the various pearls, the various attendees may have in helping you learn different ways of doing things that you may not do back in your own institutions. When do you consider fixating the cervical-thoracic junction? Well, in lung constructs of the cervical spine, for example, to back up multi-level degenerative disease. If you do a multi-level seizure from the front, you want to back it up with a lung construct from behind. In the case, obviously, of cervical deformities, spinal reconstruction for neoplasms, trauma, and then in post-infective instability. These are the situations where most commonly you may be using lung constructs posteriorly that cross the cervical-thoracic junction. Before we get into the techniques, let's talk a little bit about the biomechanics. You know, you typically know there's a certain degree of lordosis. The devilish showed there's an average range of lordosis, but these were studies done primarily on cervical x-rays themselves. The cervical spine is a part, obviously, of the entire spine in how we stand globally in our global spinal balance. So cervical lordosis can change dramatically depending on how the patient wants to compensate in order to see the horizon. So these are the things that one needs to keep in mind. If you're going to do a long segment fusion, you're changing the biomechanics of this patient's spine forever. You need to understand how that will affect how they stand and do, you know, the daily activities. And it's going to put a lot of strain also on the posterior tension band if you fuse somebody with a flat neck type construct. And here you can just see, here's a patient who had a fusion done, an outside substitution, which basically fuses the patient into positive kyphosis. But when we changed the overall global balance of the thoracolumbar spine, cervical spine adapted accordingly. And you can see how that changed dramatically, right, just from a change in position of the rest of the patient's spine. We always, we're here to pimp you guys, obviously, so let me just try that. Here in front, blue shirt, typically in the lumbar spine, in a static position, what are the loads in terms of percentages on the anterior and posterior columns? You know that? It's about 50% on the anterior column, 50% on the posterior. Typically it's 80-20, okay, and that can change depending on how you balance. Now in the cervical spine, it's a little different. In the cervical spine, the lateral masses aren't like the posterior facet joints in the lumbar thoracic spine. They actually take a much greater load. And basically, if you were to count the posterior elements or the posterior column, the facets along with the lamina, that takes about 64% of the load in the cervical spine versus 36% along the discs in the anterior column. And that's why posterior spinal fusions in the cervical spine tend to fuse better than in the lumbar spine, because there's a greater load, and according to Wolff's Law, you're going to have a better fusion mass if you arthrodise adequately. And we're going to get into that too, because all these fusion procedures we talked about mean nothing if you don't get bone growth, right? Another key thing to keep in mind, when you're approaching the spine posteriorly, there are a lot of other elements that play a role in stabilizing the spine and determining what that posterior tension band is. And you can see just the array of muscles that attach to the lamina and the spinous proxies that you're going to eliminate or detach significantly when you do a long- segment fusion. And in doing so, with or without a laminectomy, you can eliminate a lot of the force vectors that are applied to a normal spine and spinal balance. And over time, as the spine degenerates, those force vectors can change and can create what we typically see as a swan neck deformity. And that's why we find, and it's not 100% of the cases, but it can be as high as 20% of the cases in long-segment laminectomies that patients come back with a certain degree of kyphosis. Obviously, that can also go hand-in-hand with progressive stenosis, which, as we all know, can be a cause of myelopathy. And if you're in a situation like this where a patient's been radiated for a tumor following a posterior procedure to eliminate that tumor, you're going to have a much higher incidence of kyphosis over time. So being able to address the cervical-thoracic junction to avoid these problems, which present with a certain degree of risk to fix later on, is a big plus. So let's look at some of the fixation techniques. There are cables and wires, lateral mass plates, these are kind of the older options, although there are still some sublaminar bands and wires that are being used today. The most common are your polyaxial screw rod constructs. Those consist of laminar screws, in certain cases, pedicle screws. I think yesterday we talked about C1-C2 fusion and C2 pedicle screw placement. Lateral mass screws, which we'll talk about a little bit today, and laminar hooks and clamp constructs. But as Mike Wang mentioned last night, to have a larger array of options in your armamentarium is a big plus, because when you're dealing with cases that have a very abnormal anatomy, and sometimes that anatomy isn't quite clear on imaging, you have to have the ability, intraoperatively, to use different techniques to possibly be able to get the final goal that you're shooting for. So like in that patient I just showed, I think I put every screw that you can think of. Pedicle screws, lateral mass screws, laminar screws, we even did a sublaminar hook and a lateral mass screw that went down into the costal-flatebral junction to be able to get adequate construct stabilization in a patient with significant congenital deformities. Let's talk about the more common polyaxial screw rod systems. In the old days we used to use these plates, those sort of fall on the wayside, and now we have these polyaxial screws, which are much easier to put together. But the placement of screws follows the same concepts. You are getting your fixation point into that articular column, so that middle column primarily. And you have to be aware in doing so of two major structures or areas of danger. That is the neuroforamen and the vertebral artery, which stand very close to where you want to put your screw. There's a very close, obviously, relationship between the nerve root and the pedicle, as well as the vertebral artery and the lateral masses. So keeping in mind where those structures are that you're not going to actually be able to see, but you can use anatomical landmarks that you are able to see on your exposure to assess where those are most likely located. Furthermore, you have to keep in mind the angulation of your articulating facets in place in those screws. Because if you want to fuse, let's say, two C6, but you don't want to violate the C5 segment, you really want to maintain that facet intact. When you bust a facet or destroy a facet articulation, it causes a significant amount of instability in the cervical spine versus what would happen down the lumbar spine. The facet articulations of the lumbar spine have more stabilizing mechanism in rotation. In the cervical spine, it's inflection and extension. So the chance of progressive kyphosis over time, if you blow the facets, is much higher. Let's look at some of the most common techniques for placement of these screws. Basically, Roy Camille and McGurl were the classic first two that came on the scene. There are many combinations and variations of these techniques, but they follow two different trajectories that encompass everything else in between. In the Roy Camille technique, you place your screws perpendicular to the cortical surface of the lamina, or the lateral mass, that is. The goal is to be below the nerve root. In McGurl, the entry point is slightly medial and lateral to the nerve root exit zone. You angle your screw upwards and outwards in order to avoid the narrow foramen and the transverse foramen, where the vertebral artery is most likely located. Here's an example of your entry points for McGurl. You'll do this in the lab. Identify your lateral mass. It's usually a box-type shape. You're going to transect it in vertical and horizontal fashion, and your entry point is just slightly up and over. Now, I personally have a different technique. I'll go a little bit down and over, but it's very similar to what McGurl did overall in terms of trajectory of my pilot hole. For Roy Camille, you just pop it right down the middle. Your trajectory in the Roy Camille is going to be, as I said, perpendicular to the lateral mass surface. So, you're going straight down. If the screw, obviously, is too long or too inferiorly placed, you can disrupt this arcticline facet. Not to mention, if you go a little too long, you can hit the transverse foramen. So, most people tend to try and avoid this technique. At least, I don't know how many of you guys still use a Roy Camille-type technique, but it seems to me that the McGurl is a little bit more preferred because you get a much longer purchase distance of your screw, and obviously, each thread on the screw is going to increase your pull-out strength, each thread you can put in there. And if you were to go bicortical, there's a much lower risk of injuring the nerve root as well as the transverse, sorry, the vertebral artery in the transverse foramen because you're aiming away from it. So, you can go about 25 degrees out and 30 degrees up in most cases, up until about C6 and C7. It varies somewhat because those lateral masses are thinner and have a slightly different angulation. Bicortical purchase, I do it sometimes, especially in older patients who have osteoporotic bone, but the lamina are pretty cortical. They're not as osteoporotic as the rest of the bone typically is, and that's why it's also important to tap these holes. What does a tap do? Why do we tap holes? And these are just dumb questions, but they have a meaning. I'll ask somebody, maybe doesn't go to Home Depot as much as most of the guys here. Why would you tap a hole? Well, it creates the ridges. Is that the main reason? Tapping eliminates bone. It cuts into the bone, okay? So, when you place your screw, you're not expanding the bone as much. So, if you have osteoporotic bone, typically you don't really need to tap it. You want to use your cortical bone, whatever's there available, to increase your torque placement of your screw. But in a cortical bone, what happens is if you expand that bone, you can split it. Does anybody ever put a screw into a piece of plywood and split it, or do a 4x4? Well, if you split a lamina or a lateral mass, you've lost your purchase. So, in tapping that preemptively, it decreases the chance of you splitting and cracking the facet. And here's an example, just a schematic view of how that screw is placed. Earlier, guys were talking about foraminotomies. Where is the nerve root within this foramen? Is it, I'll say, how many people think it's right there? Raise your hand. There's one. How many people think it's right at the level of this, right in the middle? Nobody? How many think it comes right over the, right there? Yes, that's where it is. Okay? It changes as you go down the lumbar spine, but up in the cervical spine, the nerve root comes up over the pedicle. And as I mentioned, I do it a little bit differently. I place my screw, my entry point right about here, and I use a McGirl-type trajectory. I talked earlier about the articulating facets and the diagonal or, I don't know how you want to call that, say, diagonal trajectory of it itself, from front to back. It's important to keep this in mind because if you drive a screw through here, you're going to disrupt that, and your fusion surface, especially if you've done a laminectomy, is this. Okay? So, in placing your screw, you need to keep that in mind because you need to decorticate that lateral mass deep, and thus remove all of this cartilaginous tissue on the facet articulating surface. If you put your screw right up in here, and then you try to take that away, you're going to lose your screw purchase, right? So, keeping that in mind when you place the screw is important. Furthermore, if you're doing an osteotomy, let's say you want to take a patient and release them posteriorly, like in a trauma, where you want to take down the lateral, the facet articulation somewhat to reduce your perched facet. Or, if you've got a guy who's in kyphosis, and you want to try to gradually bring them back in extension, releasing the posterior elements, you've got to keep in mind that you're taking bone away when you do a Smith-Peterson osteotomy, right? And that bone is taken away from where you want to place your screw. So, that's another thing to understand and to study preoperatively, and where you decide to place your screws and how you place them, because you can do a great job, and then you go to the osteotomy, and you blow all your screws, and you're starting over again from scratch, okay? And here's an example of a small Smith-Peterson, where the inferior and superior articulating facet surfaces are eliminated, but it still has space for the screws, and the adequate purchase. I think it's a better view out over here. And that one or two millimeters of osteotomy, or bone removal, is sufficient to get a lot of correction in many cases. More so if you do a pedicle subtraction osteotomy, which in some cases can be done at T1 or even C7, and for example, in an ankylosing spondylitis case, or a patient who's gone into positive kyphosis for whatever reason, be it an infection or so forth. But in these cases, too, you need to keep in mind that you're taking away a pedicle, and therefore, any facet purchase at that level, you need to plan ahead of time where your other screws are going to go. Here's an example of a patient with ankylosing spondylitis who didn't really need a pedicle subtraction osteotomy because she had one segment that was mobile that opened up, and just doing a Smith-Peterson, we were able to bring her back. Here's a little trick, and I love this course because we can kind of provide some of our tricks to you. And I learned this trick at this course from Mike Wang. I don't know if Mike's here. Is Mike here? He's not. In doing these reductions, this in theory could be a very unstable spine. So what we do is, at least what I do, I'll place a rod with a hinge, and several companies have these hinge rods which are used for occipital cervical fusion primarily. But I'll use that hinge right at my hinge point, and then as I translate the head back under direct visualization, this rod is giving me a good reference point if the spine is translating one segment compared to the other, which could be disastrous. And then once I've got the reduction, and these screws have slid up along the rod as they should, I'll just lock down that little hinge and then put a permanent rod on the other side. And in the case of ankle and spine, the latest, these people want to fuse. So one could consider going from the front, but this lady fused very well without having to do that. Top of the construct issues is very important. Lateral mass screws do not have great pull-out strength. They do not give you the ability to reduce as well as a pedicle screw in the thoracic spine or correct a deformity. There are primarily a, you fix it, hold it in place kind of construct. So you need to keep that in mind. And there are situations in which, though, you need to put a little bit more strength on your C7 or C6 screws, and that's where other fixation options come into place, be them pedicle screws, for example. Also, bottom of the construct issues are important. As I mentioned earlier, the lateral masses at C7 and C6 are smaller, okay? So if you do a long construct at C7 and you want to put a lateral mass screw here, the likelihood of that failing or pulling out is a lot higher if you just cross the junction and go to T1 or T2. And the amount of motion you're going to take away from a patient by doing so is minimum. Most of the motion in the cervical spine, I got this little beeper, let me aim at somebody here. Young lady in scrubs right there. Gotcha. How much motion in percentage overall does somebody have from C4 to T1? What I could do normally, what I'm doing right now, how much of that motion is dependent upon C4 to T1 being mobile? All the way around, it's about 20 to 30%. The majority of your motion's going to be at C1, 2, and occipital-cervical junction. That's about 70 to 80% of flexion, extension, and rotation in most cases in a normal patient. Obviously, as you get degenerative changes, things may change. So if I cross the junction at C7, T1, I'm really not going to take away a lot. On the other hand, if I don't cross that junction, one or two things could happen. Either my screw could pull out because there's a lot of strain at the bottom of the construct in a very weak purchase point, and I have a big lever arm, or I'm going to put a lot of strain in that cervical-thoracic junction, which isn't used to moving 50% overall, and can have progressive degeneration and therefore going to typhosis. So I tend to cross my junction often if I find myself needing to stop in a long construct at C7. I mentioned earlier a little bit about transpedicular screws. The nice thing about this course is you can do these on cadavers. You don't want to try one of these the first time in a real-life situation because they do have a certain degree of complications, and I'll show you some examples of that, but they are a great option to have in your armamentarium. They offer excellent pull-out strength. They can readily be exposed without difficulty. The severe trajectory, although it can cause some issues in terms of transition because you're coming from the outside in versus the inside out. So if you want to connect two screws that are in close proximity, you may need to use an offset connector. There's a definite learning curve, and you might want to start that learning curve today. Sometimes it is difficult to assess and draw from the x-rays that level because at the junction in the shoulders, it's really hard to see what you're doing. So you need to have good anatomical markers and be able to assess those straightforward yourself versus relying on navigation. Although some people may want to use narrow navigation, that's a whole other issue. Here's an example of the difference between a lateral mass screw trajectory and a pedicle screw. You can see the diameter of the screw is obviously greater, and that gives the screw more strength. The length is greater, which gives a higher pullout. And the trajectory, because it's medialized, also increases your pullout. So this is a screw that you can work on with deformity. If you need to correct deformity, you can put some compression on that screw. This one, you're really much less likely to be able to do so. You always want to evaluate your preoperative CT first because there can be significant variance of where that vertebral artery is located, and you don't want to put a screw through it. And you want to assess if the pedicle is large enough to accommodate a screw. What is our thinnest screw in the cervical spine? Three fives, right. Now some companies are thinking of coming out with three O's, but three fives are smaller. So if this is not a three five or a three O at minimum, because some pedicles can dilate in younger patients, is not adequate to accommodate for a pedicle screw, then don't even give it a try. I always recommend exposing the medial border of your pedicle. If you're going to put a pedicle screw at C7 or at C6. And it's not a hard thing to do. It's a little laminotomy, almost like a fremanotomy. You can feel that medial border of your pedicle. It's safe because the spinal cord is much more medial and direct visualization, you can drill that screw out. These aren't the kind of screws that you can use a probe with because the cervical spine is mobile. It's going to push away from you. There's a good chance you can pop the Mayfield head holder if the patient's in a head holder. And it's a very cortical pedicle. So it's not going to give you an opportunity to go down with a pedicle probe as easily as a T1 or a T2. So usually you need to drill it under power or using a tap. And to do so, it's a lot better if you can see the pedicle and shoot right down the canal of that pedicle. And I'll show you guys how to do this intra-optically. Expose, palpate your medial border, and then you can assess where your entry point is and just drill straight down. This is an example of some pedicle screws and how that helped in correcting for deformities that obviously were much greater corrective result than your typical degenerative case. And another example here. But these can cause complications. This is an article from Mabumi showing several of the complications from his pedicle screw experience. And this is the guy who's probably done more than anybody in the world of cervical pedicle screws overall. You can go into a vertebral artery. You can go into a canal. And therefore, again, I typically will not put a pedicle screw above C7. I don't see the need in many cases. And if I do, I want to expose that pedicle. Let's talk about T1, T2, okay? When you cross the junction, you go into thoracic spine. Now the situation's a little bit different. You have a relatively stable segment. The thoracic spine is hypomobile because the rib cage stabilizes it somewhat. And you can put a little bit of pressure on your pedicle. But you need to understand your entry points and your trajectories. And T1 and T2 are very different than all the other pedicles in the thoracic spine. They're a little bit more similar to C7. So they come in much more medial and your entry point is much more lateral. And that can be a little daunting sometimes because it looks like you're shooting your probe right into the canal. But if you don't go in that direction, you're gonna end up a lateral and although it could be an acceptable screw in the cost of vertebral joint, it's not gonna have as good a pull-out strength as one that you place fully down to the pedicle. This is a schematic view of Lenke's thoracic pedicle screw placement protocol. And you'll get a chance to do these in the lab all the way up and down the thoracic spine to get an idea of how the entry points are. And the best thing is just sort of memorize these and where those entry points are. But you can see clearly at T1 and T2, they're much more lateral than in T3 than they are at the other levels below. In using the probe, you typically want to initially aim towards the canal. This portion of the canal is actually quite hard to pop through. I don't wanna say you wanna try to do so, but it'll help guide you into this funnel that consists of the initial portion of the pedicle. That's about 10 millimeters of depth. As you probe further to about 20 millimeters, you wanna cheat medially along that medial board or lateral border of the canal till you get past the canal entirely, and it's usually around 20 millimeters depth. At that point, if you're in body, you're home free, you just turn your probe medially and extend into the body. Now, if you were to break out laterally across the vertebral joint, not to despair, you can always vary that and enter back into the body. And that is typically an acceptable screw with pretty good pull-out strength. But your entry points can be even more lateral at this point than it would in initial pedicle screw placement. Many studies showing safety of placing these screws and with navigation, those safety data points have gone even up further. But as I mentioned earlier, there are acceptable screws that aren't perfectly placed as long as they're not up against vital structures that can cause, obviously, other problems. It's been shown that if you have a medial breach, two to four millimeters, it usually doesn't cause neurologic issues and the pull-out is acceptable. If you have lateral breaches, less than six millimeters, and within the cost of vertebral joint also show that they have adequate pull-out strength. So you don't really necessarily have to go back and replace those screws. They're not perfect, but they'll be, in most cases, adequate to get what you're looking for. I talked about combined options, when to back up an anterior construct with a posterior construct. We mentioned that sooner, but I'm gonna just skip over this to finish up. Here's an interesting construct that we've been using more and more in deformities or in tumors that are gonna be radiated, because we know those patients aren't gonna fuse, so we're highly dependent on the instrumentation. And those flimsy rods are exactly that. They're flimsy. 3.5 rods and 4.0 cobalt chrome rods can snap pretty easily, and there's a lot of strains to be put on that. So sometimes you can back up your construct with a 5.5 rod or a larger rod construct. And what we did here is a sublaminar fixation with a sublaminar band above, and used this long 5.5 rod connected to thoracic screws, because as you know, the 5.5 rod diameters typically don't go with screws that are any smaller than 4.5, so it's really hard to use one of those screw heads up into the cervical spine. But you can create these hybrid constructs with offset connectors that can give you a lot of strength. This isn't gonna break. The guy can't break this. He can pull out of screws, maybe, but he isn't gonna break the rod. And sometimes, especially in situations where you've had failures or multiple failures, and we've all seen those, doing the same thing twice is always a mistake. So if it doesn't work the first time, try, try until you get it right. But if you just repeat the same mistake over and over again, you're gonna have the same result. How do you fixate at the top of that rod? How's it connected to the spine? Over here? This one here? No, no, the slide before. Oh, there's a couple companies that have the sublaminar bands. Zimmer, Uclamp, Lobus has the new silk product. I like it over a Sanger cable because a Sanger cable tends to cut through the lamina more. And these bands reduce in a, they don't slide the band, it just reduces in a parallel fashion. And they're nylon bands, so they don't cut through as much. So I'll place those sublaminarily, let's say, in that case, I think it was C2 or C3. And then I connect that to the 5-5 rod and then offset connectors to the 3-5 rods. Rod contouring, obviously, we talked about purchase points, how important those are. When you have situations, this is a guy with neurofibromatosis. And who doesn't know this, neurofibromatosis often associates with spinal deformities. And they're due primarily to the fact that these patients have duralectasias. And the duralectasias, year over year, will erode at bone and they'll take away pedicles and vertebral segments. And then the spine can sublux and scoliosis, as it did in this patient's situation. But because of that amount of erosion, there are very few purchase points in a situation like this. So you need to have, again, in your back pocket, multiple options. And assure that you have adequate purchase points. And in this case, we had to go to occipital, even though the occipital cervical junction wasn't a pathologic factor. We ended up eventually coming back and taking out the occipital plate about a year later. And he got some motion back once he was fused. But we needed to go higher in that sense. Where the mistake was here was the flimsy construct below. And you learn, obviously, from your mistakes. And you can see in a situation like this, it was destined to fail. These three little dinky screws and this little rod with this huge anterior void in the front wasn't gonna hold up very long. And within a month, obviously, it fell forward. So follow-up, the point to this is, follow-ups are very important. Now, if I had done maybe a more solid construct first time around, follow-up wouldn't have been as important, but it's always important in any case to make sure that what you've done is gonna follow through. And we ended up then supplementing that posteriorly and we didn't really lose much. And as I said, a year later, we took out his occipital plate. So always keep in mind that, what kind of rod you're using, if it's gonna hold the forces and if it's adequate. If not, you may consider anterior supplementation. If your purchase points are concordant with your rod pull-out strength, if you've got a very big lever arm and only one or two purchase points that are flimsy, you might wanna think about going longer. And lastly, when placing your screws, remember you need to contour a rod. You need to be able to connect that rod. And the more you bend a rod, the more likely you're gonna create stress fractures within that rod, and the rod will snap very quickly. Titanium has a little bit more give, cobalt chrome a lot less, but after a while, it'll just snap if you've got a stress riser that you created with bending. So often we'll do cases, the cases of our residents and fellows, and I'll let them play with the rod for about half an hour and they finally get it perfect, and then I throw it out because they've just bent it too much. You need to, and that's a question, just getting used to it and practicing more and more. Last tips and pearls. Avoid stopping a long fusion at C7, as iatrogenic kyphosis risk is relatively high. T1-2 pedicle screws are solid alternatives to securing the caudal portion of a construct, and the trajectory of a T1-2 pedicle is more medial. It's higher risk for neurologic deficit because of that, but overall, once you get used to placing these screws, you understand anatomy, placement is pretty much safe and reproducible. And I think, unless there are any questions, we can go ahead and go to the lab. Anybody have anything to ask?

cervical-thoracic junction

fixation techniques

cervical scolateral mass screws

biomechanics

fusion results

screw placement

vertebral artery