Good morning, I'm Joe Chang with Vanderbilt, and I guess it's my privilege to tie this all in. I just want to thank Bob and Justin for running a great course, and as chair of the Double N SEPM Committee, I can tell you that these resident courses are really one of the crown jewels in what we deliver as far as education, and this course, along with Praveen's course with Pat Jacob in the fall for the resident courses, again, are just fantastic in a sense of how well organized they are and the content they deliver. So what I'm going to do is I'm going to talk, give this talk about curve correction techniques, and in a way I'm going to try to tie this all in to some of the things you talked about this morning. What Bob was talking about and how important these concepts are cannot be understated. If it was just a technique, you know, learning how to put in pedicle screws, residency should be what, a month? I mean, how hard is it to put in a screw, right? How hard is it to use a bone or drill and drill off the part of the skull? I mean, these are not hard things that you can't do in your own garage on a piece of wood as far as what we teach. The hard part is actually the pathophysiology, the pathomechanics, and really understanding it. And that's why I always kind of make a joke that if we didn't care about the outcomes of the anatomy or the pathophysiology of things, spinal cord tumors would be one of the easiest surgeries you'd ever do, right? If you have an ependymoma or an astrocytoma in the spinal cord, you cut the spinal cord above, cut the spinal cord below, pop it out, you're done. How hard is that? The hard part is actually trying to make sure patients do well after surgery, and that's no different in spinal deformity surgery. As far as disclosures, nothing relevant financially, and I'm not going to talk about anything unapproved. And these are things that Bob is hinting at that is going to be more and more. But I want you to not take these disclosures in a way that's bad. Just because something is off-label doesn't mean that it can't be used appropriately. So for example, how many people think epidural steroids are standard of care for a lot of degenerative diseases? Someone comes in with a below back pain, do you ever see people order epidural steroids? Did you realize that there is no steroid that's approved for use in the epidural space, so all epidural steroid injections are actually off-label use and are not FDA approved for that? No, and so that's one of those things where just because something is considered off-label doesn't mean that it isn't something that can be applied well in treatment of your patients. Now the technique of curve correction really depends on what you're trying to correct. And so a curve is not a curve, and you've been hearing about that this whole morning. And so this is just a case example to kind of, again, drive a point home, where you start off with a patient like this who went to see another surgeon who correctly diagnosed this patient with flat back back in 2004, said, you know what, I know how to fix this. We're going to go in there, we're going to break up some bone, not a lot of central stenosis or not a lot of decompression that needs to be done, but I can fix this. Position the patient on a table, but this is all they could get. And so they removed the bone, they kind of did the laminectomies, the facetectomies, and that's all they could really get. The patient's spine didn't move, so they said, oh, it's pretty rigid, I'll just put in my screws because it can't do much more than this because it's pretty solid, and I'll just put in a bunch of screws from L2 down to S1, including some inner body spacers. Well then this is what you end up with, right? With a patient that's fused now in that area, so now the curve's changed as far as what you're dealing with. Then of course, as you've been hearing about this morning, that's not an optimal situation where now a patient who's considered to be still sagittally imbalanced will continue to progress into this, where now they start forming an adjacent segment or proximal junctional kyphosis or degeneration of that segment. And so as time goes on, the surgeon says, you know, I know the patient has this intractable low back pain after my surgery. Surgery went fine, the CT scans show a solid fusion, so I'll just go ahead and take out the hardware, right? Because it must be painful hardware, because there's plenty of bone in that area. Now the patient still continues to deform, the cages start displacing posteriorly, even though they were supposedly solid in there, and so this is what kind of progresses to something like this, where now the patient has a severe deformity, as you can see there. So then you go in, you do a vertebral columnar section, you kind of get the patient straight. Patient does well initially, but there's also other issues on this, where if you look at this construct, you start thinking, what kind of stress and strain are being put onto the hardware? Is this hardware going to hold up over time? Where is the bone going to grow into? Where's the fusion going to take? And those are very important points, because without thinking about that, with a patient still corrected but still slightly sagittal, you're going to put a lot of stress across that area of the moment, and you start getting these rod fractures that you can see right there. And as this continues to fracture, you realize you're going to overwhelm using the stress point along the cage, causing this to progressively deform and fracture through the areas that previously had healed in, and so then you start using other techniques, including quad rod techniques for this. I'm going to talk a little bit about some of the options when you're talking about curve correction, of kind of designing constructs to hold, withstand the stress of that junction, that the patient's been holding stable for a while now. And so a deformity is not a deformity, and that patient, specific patient, started off like this, who came in with low back pain, and ended up like this before she had to undergo a lot of these revision surgeries. And so this is something where I think it's important to kind of keep in mind about what you're trying to do and the ultimate outcome of your treatment. So the type of deformities are important because how you approach curve correction will depend if it's flexible or if it's fixed, and frequently you'll be addressing both at the same time. So for example, this patient who had a prior low lumbar fusion with adjacent segment degeneration and deformity, as you see there, has a combination of a curvature that you can correct, you know, by just manipulation, flexible, but then also has a fixed area that has to be broken down unless you incorporate that into your overall construct. And these are important concepts as we kind of continue talking more over the next day or two about things like when you decide to treat just a fractional curve, when you have to treat the whole thing, but a lot of those decisions or answers come from how much you want to treat and what you're trying to treat overall. The patient assessment issue, again, can't be understated. One of the things that you've heard about is 36-inch films. But not only 36-inch films, so make sure there are 36-inch films with a patient on a hand-on clavicle or a crossed hand pose so that they're not supporting themselves on the bar, which frequently is used in a lot of x-ray rooms, because that's going to throw off your ability to calculate, per se. And so that is something really important, that what you're measuring has to be true to what the patient's natural position would be if they were at home walking around, etc. The other thing is that these fusions that people are doing sometimes are interesting because you'll have solid fusions, but then we see a lot of these where people call them soft fusions using dynamic stabilization and things, but at the end of the day, they're not really fusions. They're just functional pseudoarthrosis. And so again, so if you put in non-rigid rods without a lot of good bone graft in there, even though it's not moving on Flex-X, without a lot of haloing or clear zones on the screws, it doesn't mean that it's a solid fixation. And so your approach to these patients will be, again, something that you'll want to consider as far as flexed or fixed. So one of the first steps in curve correction actually is how you position the patient on the table. And you've heard a lot about the patient's spinal alignment, and so how you position a patient on the table will then start determining where the spine is curved. One of the most easiest things to show you, for example, if you put someone on a Wilson frame, you can imagine the spine opens up, right? You take the lower doses, you turn it into a kyphosis, makes laminectomies easier, especially if you're doing MIS decompressions. You don't have to deal with the spinous processes, but you can understand that if you put a patient like this, for example, when MIS was starting to take off, we saw a ton of MIS fusions where people were doing them on the Wilson frame so that the rods and the markers that they put in the guide wires didn't get in each other's way because they splayed open. The issue is that we saw a lot of flat backs being fused into that place with MIS techniques, and again, this is something to kind of consider. For the Jackson frame, putting patients in lumbar lordosis is important too, but you remember the whole concept of three-point bending. Just because you add a lot of buttressing to the chest wall is not going to cause the spine to curve, right? It requires both of those points separated at the pelvis and at the clavicle region or the shoulder region with an area in between that allows the belly to sag. If the belly still doesn't sag or if it's stuck against the Jackson frame on a large patient and you put a lot of extra padding there to help give an abdominal support and you just add a lot of padding to the chest area, all you're doing is putting a patient in really a sense of reverse Trendelenburg, not really causing the curvature that you want. So this is really important, especially for those of you who are still at the level of training where you're responsible for positioning all the patients, to realize that your position of patients will make a huge difference in how we correct curves. So for example, in this situation, if you put them on a Jackson or a Wilson frame in this posture, there's nothing that you can really do with the hardware once you start surgery to correct that curve into a good lordosis. I mean it's almost impossible unless you lift the pelvis and the shoulders up off the bed, which isn't really going to happen with the hardware that we use. One of the things that you hear about is a lot of correction on a table, and this is a picture of us doing this. So what I'll do is I'll use a sheet. So one person will hold their shoulders stable while when you're lifting up the hips, and that's me grabbing the hips, and what you do instead of just pulling, you want to lift up and over because the friction will prevent you from really getting a lot of movement or reduction unless you kind of lift up and over. And think of it the same way as when you're putting people in cervical traction about the vectors of force that you're trying to apply to get that initial reduction. You've heard a little bit about osteotomies, and this is something to remember, that osteotomies are something you should already be pretty familiar with in the sense that if you take care of trauma patients, if you think about it, they're all at the ends of the same spectrum. So in a traumatic injury, you're looking at what broke to understand what made it unstable that you need to make it stable. On deformity, it's the other end. You want to know what you can break to make it unstable so that you can cause it to manipulate in a certain way. So if a traumatic patient with a bipedicular fracture or burst fracture, you're like, yep, if we don't stabilize this, this is what's going to happen in three months as the patient continues to deform, whether it's listhesis, progression of the fracture, kyphosis, etc. You're doing the same thing with your osteotomies, just the opposite. You're saying, heck, what do I got to break to cause it to cause listhesis, kyphosis, lordosis, etc. So the same concepts that you're applying across the spectrum are the same things that you'll apply within lumbar deformity surgery. I'm not going to belabor this various types of osteotomies, but the whole idea of just knowing what you need to remove. So one of the keys, for example, in subtraction osteotomies is that one aspect is just wedging this out. But why not just wedge it across this space, what we call a kyphectomy? And there are certain CPT codes for kyphectomy or three-column subtraction. And then there's also pedicle subtraction osteotomies. One of the big keys is actually preservation of the neural elements. So when you're doing a PSO, remember, you're creating a super foramen, you're cramming two nerve roots now into one open space as you collapse it down. So that if you don't clean out the pedicle and create enough room, including removal of the PARs above and below for that space, you're going to end up with a great correction in a patient with a severe radiculopathy or neurogenic problems because of the nerve injury as you compress that area down. Same thing with VCRs or vertebral column resections. When you look at these pictures of VCRs and how they're done, you're thinking to yourself, wait a minute, that looks like a bilateral extracavitary approach. And the answer is yes. And so that's why it's so important to remember, if you're doing a complete laminectomy and facetectomy or what we call ponti-osteotomies, and you're like, hey, that's the same technique as I do a gill-type laminectomy for spondylolisthesis, yes, that's the same technique as I use when I take off the lamina and facets to do a T-lift, yes. So you start realizing that you know these techniques. You're now just applying it in a different scenario because you have different outcomes that you want, i.e. the curve correction of the patient. Praveen already talked about this in a sense that there are certain percutaneous techniques of what you can and can't do. And this is a patient I treated years back where you realize that percutaneous techniques have its limitations. There are certain times you could do it, certain times you can't. And so if you think about trying to pass a percutaneous rod through there, imagine passing a percutaneous rod in an S-shape, almost impossible to get a T4 to pelvis rod passed percutaneously because it doesn't flow that way. So curves with a single plane deformity are much easier to address that way. If you need to do large global correction methods, for example, in this scenario where if you want to anchor, say we're using a Galvinson-type technique, using a long lever arm and then use that to kind of crank it over. These are things obviously you can't do MIS. But also it's important to realize how much exposure you need to get that area open so that you can manipulate the spine in that. There's also cross-rod techniques where you implant the top rod on one side, in the lower spine you implant it on the contralateral side, and just like a pair of scissors use both of them as a fulcrum to kind of get it over to get your correction. These are better for flexible curves and not really well in rigid curves only because you're not going to overpower the bone and most likely going to end up with pedicle fractures if you try this overall. Other global correction methods are things like in situ bending where you put in your rods based on how the patient is and then you bend it overall. Now one of the concepts here to remember is that it requires a more ductile material. So for example, if you're using 316L stainless steel system, easy, great, that's typically what's used. If you use a cobalt chrome rod, which is very brittle, meaning that's like a pretzel, doesn't bend real well in situ bending, you have to over bend it to get it to stay in place, not a good idea to use this technique for that. So your choice of materials and your choice of techniques has to marry each other to make it viable and this is something that during the lab you should ask your table instructor these questions about why they choose the instrumentation that they choose and the techniques they use due to that. The de-rotation technique is a nice technique and it's like swinging a jump rope, but because it's like swinging a jump rope, your angle of coronal deformity should become the angle of either the lordosis or kyphosis that you're trying to introduce into that segment, right? Because as you rotate the rod, whatever you have in your coronal plane will then become what it is in a sagittal plane. So this is nice for kyphoscoliosis in a single plane and I like to use it for my, as Praveen was talking about the mini open techniques of how you're able to use one side, correct that area down, what I call my working side, and then the other side's my neutral side where then I put in my rod and my screw systems with a lot of stress to help supplement the strength on the other side. And so these are some of the techniques that you would want to try when you're in the lab today. There's also segmental correction methods where if you have a patient with a coronal imbalance, but from a sagittal standpoint, they're actually pretty well balanced, you can just fix that coronal imbalance pretty easily by either compressing down in areas where you did facetectomies or if you did release by taking down the joint capsule, you can just distract across that area to fix small curves in that sense. And that's something that you can try again in the lab as well and the whole idea is to open and close spaces and close the open spaces per se. Now as you're doing this, also remember the construct forces that you put onto your spine. And so not every spinal level is going to be amenable for you to apply that much force. So for example, in the L4 level, you can see that the pedicle's pretty oval and the strength of the pedicle screw is really the purchase into the cortical wall of the pedicle going in. But if you try the same thing at L1, which is more oval shaped, you can imagine that as you apply distraction or compressing, that pedicle screw has a little bit more room to slop because it's a round structure and an oval shape, so you're going to be limited by the lateral walls of the pedicle, which means it's going to potentially go up and down a bit. And that's something to remember as you're applying these forces to not exceed that. The other thing that I want to point out as far as curve correction techniques, again, not just the concepts of the techniques for deformity correction for your osteotomies, but not only how to put in the screws, but think about the implant size that you want to put in. So for example, every one of your manufacturers that you'll be working with will have a material data sheet to tell you what to do, and this is what I'm going to recommend that you think about. Two components, one is yield strength, which is the overall strength of the rod system or screw system, how much energy it can absorb before it fractures. The other one is stiffness, right? You saw in your force-suspection curve that slope of the line, and that's brittleness. So just because something's stiffer doesn't mean it's stronger. So like a pretzel is pretty stiff, but it can fracture pretty easily, right, versus a rubber rod or something like that, which is very malleable, not very stiff, but won't break as easily. The reason why that's important is that typically most people use 635 or quarter-inch commercially pure titanium. It has a fairly decent stiffness, easy to bend, easy to cut because it's also very weak. It's within the same yield point or strength range as 4.75 cobalt chrome. If you move it over to cobalt chrome rods, 5.5 cobalt chrome rods or cobalt chrome plus, sure, it's a little bit stiffer, but it's also stronger than commercially pure, but it is not as strong as titanium alloy rods if you want to introduce something that has a lot of strength in your construct and hold that up. And stainless steel is still a good option. So stainless steel, 316L stainless steel, not only has a good stiffness, but still has a high yield strength. So that quarter-inch stainless steel is still a good option for deformities depending on what type of deformity and how much load you want to apply onto that construct. And so don't be surprised if you're only using commercially pure titanium rods and you're getting a lot of rod fractures. Don't be surprised if you're like, hey, I don't understand why these keep breaking. On the other hand, if you are sustaining a lot of rod fractures, even titanium alloy, this is when you want to add a third or fourth rod into that system to supplement that strength as far as what you're designing. So just kind of keep these concepts in mind as you get into the lab today. The other thing is when you're looking at these curve correction techniques, just keep in mind, do you really need to correct a curve to how you want it? Remember, it's got to be patient-centric. And so the reason I put this slide up is that a curve correction in a patient who's upright and walking is different than a wheelchair-bound patient, right? So that when you're sitting down in a wheelchair, your spine is not lordotic. In fact, if you correct a patient who's wheelchair-bound with a great lordosis, you're going to end up with huge sacral decubiti, okay, because of that. And if you think about it, these concepts are real simple so that we talk about these aspects of pelvic incidence. Take a step back. Go back to your pictures of pelvic incidence and you'll realize all pelvic incidence is telling us is the angle of the SI joint, how the sacrum fixates to the pelvis. That's all they're saying. All we're saying is that that joint is stable. It's solid. It's a true zygopasial joint. And once we know the angle of that joint, that's what the pelvic incidence really measures. And so that's why if you don't take that into account, you get a lot of issues with sacroiliac joint strain. If you don't understand the difference between these two patients with these two scenarios and patients with these chronic low back pain issues related to that by not taking that into account. So when you're doing curve correction, again, take a step back. Understand the pathomechanics of what you're treating versus just focusing on the technique. So I always tell people, you know, I had a junior resident ask me one time, wow, Dr. Chang, in training, you let us do so much. You walk us through things. How can we get so many referrals from other surgeons because, you know, 70% of our practice is actually from other surgeons. And they're like, are we that much better than someone who's been out in practice 10 years? I was like, no, your techniques are terrible, you know, compared to someone who's been out 10 years. But the issue is indications, right? So in a tertiary center, you're taking care of patients referred in, not because somebody else can't put in a pedicle screw, right? Because that's not the hard thing. You're being referred to these patients because you're actually doing the thought process, the thinking of the indications, the outcomes of how to, the indications for that pedicle screw and how to best put that in versus just the technique itself. So just remember, clinical and radiographic data is needed to assess if the curve is flexible or fixed. Flexible curves can be reduced by positioning, and that's what you always want to try first. And fixed curve requires spinal column release with osteotomies or retubal column resection. All right, thank you very much.

curve correction techniques

spinal deformity surgery

patient-centric treatment

in situ bending

osteotomies

clinical data