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Minimally Invasive Algorithms for Spinal Deformity

Praveen Mummaneni

March 08, 2021


- Colleagues and friends, thank you for joining us for another session of the virtual operating from the Neurosurgical Atlas. Our guest today is Dr. Praveen Mummaneni from UCSF. He's the vice president of Congress of Neurological Surgeons. He's also the Vice Chairman of Neurosurgery at UCSF, as well as the co-Director of Spine Center there. Tonight, he's going to talk to us about a very exciting topic, minimally invasive strategies for spinal deformity surgery. Praveen, thank you for being with us, and we're very much looking forward to your lecture. Please go ahead.

- Thank you so much, Aaron for this kind invitation to share with you some ideas about minimally invasive spine surgery focusing primarily on adult deformity, and I would also like to thank Joshua Rivera, who is my research analyst who helped me put these slides together as well. So I do have some disclosures and funding sources which are listed here. And when we talk about MIS deformity surgery, we have to ask ourselves several questions. Can we do a decompression? Can we place hardware? And with degenerative spine disease we've seen we can do decompressions with tubular retractors, we can place percutaneous screws and rods even iliac screws. Mike Wang and I, had described doing some iliac fixation percutaneous some years back. Then the next question is, if you're talking about deformity patients, can you restore sagittal balance with MIS only techniques? And that is an important question to answer. And in the past, we've had some difficulty restoring sagittal balance with MIS techniques, because you can't do the type of correction you get with open osteotomies. And then the next question is, can you match the lumbar lordosis within 10 degrees of the pelvic incidence when you do this kind of surgery? And that again, is a question that has a mixed answer. You can in some cases, you cannot in others. And again, that has to do with some of the limitations of MIS surgery. Then the next question is, how long is it gonna take you to do this surgery? Because if it takes too long, and these patients are on the table for too many hours, and they start having, you know, other issues related to anesthesia. And the last question is, once you do the surgery, can you establish a successful fusion for these patients? Are you gonna get a solid arthrodesis, or are you gonna get a pseudarthrosis? And that is also challenging, 'cause many of these adult deformity patients who are getting MIS deformity surgery are osteopenic or full blown osteoporotic. So there's been about a decade of research looking into all of these questions. I'm going to share some of that with you and hope that we can answer each of these questions as we go along, as well as do some cases to demonstrate some of the principles, that's the plan for this lecture. So when we look at adults deformity, we typically will get a 36 inch long cassette X-ray, and we will start measuring parameters to see what is the spinal balance. And one of the first parameters we like to check is we like to check the lumbar lordosis. And so to check lumbar lordosis, you have to have, you know, line crossing from L1 to S1, and then looking at the intersection of that line, and that's how you're going to check the lordosis of the spine. And there's no right or wrong number for lordosis, the actual real issue here is that lordosis should ideally be, for most patients, within 10 degrees of the pelvic incidence. I'll show you how to measure the pelvic incidence in just a second. We also wanna check the sag of the tubular axis, and this is how you measure that with the red line being shown here, you take a plumb line, and drop it from T1, and then you take a line to the posterior superior endpoint of S1, and then you check the distance in between and that's the sag of the tubular axis. Next, you wanna draw the pelvic incidence. You find the center of the femoral head here, you take a line from the center of the femoral head to the midpoint of the sacral end plate S1, and then you drop a perpendicular from the sacral end plate S1, and that is your pelvic incidence angle. And that angle of your pelvic incidence should be within 10 degrees of your lumbar lordosis which I was showing here in green, and that would be typically normal. Now, as you get to age 80, perhaps that number of LL-PI mismatch can go up to 15 degrees. The SVA normally, is typically going to be less than five or six centimeters. It can be a little bit higher, six or seven centimeters, in patients who are nearing the age of 80, because life is a kyphosis event and those patients tend to lean a bit forward. But in most adult patients, the LL-PI should be within 10 degrees, if you subtract the lumbar lordosis angle from the pelvic incidence angle, and the SVA should be within five or six centimeters. So if you have a patient who has a flat back, and you're trying to achieve sagittal balance restoration, you want to end up like this, with the SVA, plumb line, dropping basically over the sacral end plate, to end up, you know, getting you close to less than five centimeters or six centimeters of SVA, and then you want to measure your pelvic incidence and compare it to the lumbar lordosis. And if you subtract one from the other, you should be within 10 degrees magnitude of difference. That is typically correct for most patients and the adults, you know, age group of anywhere from you know, 20 to 70 years old, and when you get to 80, it might be a little bit higher. So now we've talked about, you know, the baseline parameters that we're gonna need to look at, when we're starting to deal with these MIS deformity cases. Let's go to the next slide. So, we want to do less surgery for adult spinal deformity patients because the population is aging. When we do open surgery for these patients, we get very nice corrections, but the complication rates and blood loss can be high. If the patients have comorbidities, then that can be problematic and cause complications. Pseudarthrosis rates are also problematic. A lot of these patients are osteoporotic. Now, at our institution now at UCSF, we routinely will get a bone density study, before we do elective surgery for this population. And if the T score is worse than negative two, we'll think about things like teriparatide, in order to correct the osteoporosis before we do surgery because we don't wanna end up with a pseudarthrosis situation. So, we got to figure out which of these patients is amenable to open surgery, if they have an adult spinal deformity, and which of them is amenable to minimally invasive surgery. So, you know, at first, there was no real guideline for this. People were just trying to do what they could do, minimally, invasively, and sometimes not achieving spinal balance correction. So back in 2014, we published this paper in Neurosurgery Focus. And you can see our co-authors here. Some are adult open deformity surgeons like Chris Shaffrey, Larry Lenke, some of them are MIS surgeons, you know, like Mike Wang, Paul Park, Frank LaMarca, Greg Mundis, etc. And some of them do both types of surgery, you know, for example, I'll do some open, I'll do some MIS. And then you know, some people are more MIS laterally-based, like Neel Anand and Juan Uribe, and Adam Kanter, very laterally-based. And so we had a mix of open and MIS surgeons, and, you know, other open surgeons, you know, like Justin, and Kai Ming were part of this, as was Frank LaMarca. So we put this together, and we've added it between open and MIS surgeons looking at a series of cases, and looking at the corrections we got. And this algorithm basically what it showed was that if you have a relatively mild deformity with a pelvic tilt less than 25 degrees, an SVA less than six centimeters, LL-PI mismatch was less than 10, and they have a lateral less than six millimeters, and a coronal cobb angle of less than 20. These patients did really well with really small surgery. They had a relatively mild deformity, you didn't need to correct their deformity, you could do an MIST compression, or you could do a single level fusion of . So that was class one in this algorithm. Then we have class two, which is a little bit more of a moderate deformity. They may have an LL-PI mismatch up to 30 degrees, as long as they don't have much thoracic kyphosis. We can get more lumbar lordosis by doing laterals or ALIFs, and then percutaneously fix it in the back, MIS. So that was a class two, where you can get up to 30 degrees of correction, usually about 20 to be frank, is what typically people would get with laterals, ALIFs and then . Then you had patients who had really severe deformities and had LL-PI correction of more than 30 degrees, they had a big thoracic kyphosis, those patients ended up getting open surgery, because MIS surgery was not able to restore the parameters that these patients needed. So for them, they would get open osteotomies. So that was the original algorithm back in 2014. And we used that algorithm for a good number of years, in multiple institutions. But what happened over the last seven years, six or seven years, is that patients were being treated with newer techniques that weren't really captured in the original algorithm. These new techniques are things like, anterior longitudinal ligament release, many open pedicle subtraction osteotomy, where you do percutaneous crease above and below, and then you open just the middle and do a mini open PSO in between using some expandable cage technologies or doing things like in the front and percutaneous screws in the back, with hybrid-open approaches. maybe even cutting a in the back with the facets are being removed in between the percutaneous screws. So we had to add a third class of MIS deformity surgery to the original algorithm, and this was recently published within the last year, with many of the same authors there as well. So here what we do, is we look at a new algorithm, which has the number one categories idea of a fused or rigid spine. If the spine is previously fused or rigid, you end up going to the right, if the spine is relatively mobile, you end up going to the left. So we'll start with the left. The left side really didn't change much from the original algorithm. If you had a relatively mild deformity with LL-PI mismatch less than 10, and coronal cobb less than 20, you ended up with the class one decompression only or fusion of listhetic level, single level. If you had a, you know, LL-PI mismatch up to 30 degrees, then you ended up in the middle here, and you, let me put some arrows here, so that you can see. So if you end up here in class three, basically, what you're doing is you're having to create LL-PI mismatch of more than 30 degrees, or thoracic kyphosis, or thoracolumbar kyphosis of you know, at least up to 10 degrees. You can end up with some of these corrections by doing some more advanced techniques. And that means anterior longitudinal ligament release with lateral, that means a mini open PSO, that means using expandable cage technology or hybrid-open approaches, where you might do lateral in the front to do in the back, or you may do ALIFs in the front, and percutaneously fix the back. So that is allowing more correction with new tools that were not around when we first did the algorithm. However you wanna come, you know, sometimes we still do open surgery here, and you know, that's for patients who have fused rigid spines with prior dorsal hardware from before more than five levels, where they need more than 10 levels to be treated. For those patients who need major corrections with those kinds of parameters, we are still recommending open surgery for them, and with open osteotomies, because you know, for these patients, it's hard to get the job done with MRIs only techniques, because it's just not powerful enough to get the job done and you often you have to open them up and take their hardware out to revise them and create lordosis. So that's the latest version of the algorithm that just came out about a year ago. So if we talk about MIS deformity surgery, the key thing to note, is the correction tends to come from the anterior middle columns. And it tends to come in a couple of ways that L5, S1, typically tends to come with an ALIF, and it can be hyper lordotic. At L4-5, you can either go lateral or TLIF. Some people like to do TLIF because lateral L4-5 has a bit higher rate of lumbar plexus problems, or leg weakness and numbness than the other levels, L2-3, L3-4. So some people like TLIFs, some people like lateral there, some people even like ALIF there. And if L2-3, L3-4, most surgeons in the algorithm that I'm gonna show you next, which is the minimally invasive interbody selection algorithm we're choosing lateral, and this was a survey that we ran through a good number of MIS colleagues in order to get consensus around this and looking through cases that we had done to validate that, the algorithm. So this is the so called MIISA, or minimally invasive interbody selection algorithm. This has been accepted recently to, I believe the White Channel we'll published very soon. But basically, what you do in this algorithm is you decide what levels need correction. And so if you're on the left side here, and you need correction between L1 and L3, then the next question is, do you want to maximize lordosis? And so if you want to maximize lordosis, then what you wanna do is, you wanna go down this left side, because the way to maximize lordosis is probably L1, two, three to go lateral, that gives you more lordosis than going with TLIF. A TLIF at this level does not really maximize lordosis. So that's why there's a no for lordosis TLIF, 'cause TLIF basically was only given like one or two or three degrees of lordosis, the lateral was given about five degrees or so of lordosis. And if you really wanted a lot of lateral, you know, lordosis maximization anterior longitudinal ligament, that will give you a tremendous amount of lordosis, you know, 20 degrees or so, or maybe even more of lordosis depending on what you do with anterior longitudinal ligament release. And so, at L4-5, there's a little bit of a different take on this. At L4-5, if you really want lordosis many people were choosing ALIF. And if lordosis was moderately needed, then you could still do lateral or anterior longitudinal ligament release. Anterior longitudinal ligament release at L4-5 is not my favorite operation because usually relatively thick so as sometimes the pelvis overlies it and it overhangs it, and you're working in sort of a deeper, you know, cavity there. And so I would choose typically in ALIF there, but some people will try an anterior longitudinally ligament release there. And some people L4-5. Really, I don't really need much, I just do a TLIF, and that was a level that had the most TLIFs selected, but TLIF was not a lordisis procedure, that's why you see all the arrows, all the arrows for TLIF are red here. You know, they're red here because, the TLIF really wasn't treating lordosis. L5, S1 is on the right side here. And if you really wanna maximize height or restore lordosis the main way to do it, L5, S1 is doing ALIF, there's zero doubt about it, gives you the absolute best lordosis of any procedure and interbody procedure, and the TLIF was not really giving lordosis there when you were doing it MIS. So this is the new inner body selection algorithm that was developed recently. So let's see. This is a video of doing four levels of lateral. This is when you rebase patient. I was fortunate enough to spend some time with Wang, watching him do some pretty intense multi level laterals, and we took a video, I think we sent this to Neurosurgery Focus in the past. But you can see this patient has a moderate deformity, and the goal here was to do laterals in the lumbar spine. Patient's positioned in a lateral decubitus position, and, you know, we make the patient square to the floor by using , by rotating the table for those of you who do laterals, you can be very familiar with this. And then we mark out the disc spaces. Here's the marking out of the L4-5 level. And then once we mark out the four disc spaces, we wanna do L4-5, 3-4, 2-3, 1-2 here. Here we're going to you know, make two incisions, one to do L4-5, 4-5, which is being made there, that incision, and then you can see the incision is open. Here's the internal and external obliques here, and then by using hand over hand dissection with a couple of small clamps, you can, you know, look for any cutaneous nerves. Here's a cutaneous nerve coming into view here, ilioinguinal nerve is coming into view here, so it's important not to crush or hurt that nerve on the way in. If you look for it, by doing this kind of technique, it helps you, so you can also you know, develop the plan with your finger and then use these little clamps to help you dissect your way in. I do like to do for these multi level laterals, a bit of a bigger incision, and take a look inside, to make sure that kidney, ureter, etc, are not even in my way. I don't like to do a purely blind technique with just dilators, because rarely you can strike retroperitoneal structures you're not anticipating. So we make a small incision, we take the finger and do blind dissection. We get the finger down on the psoas, then we you look with those little clamps to make sure we're not hitting anything on the way in. And then once we, you know, visualize the psoas, we put the first dilator tube down. Of course, we're going to be stimulating this dilator to make sure there's no nerves in the plexus at this area. Typically, L4-5 is the most difficult level to do. It's L4-5 typically the first level of a multi level lateral that I usually start from the inferior level and work my way up, because if you do the superior levels and work your way down, you may push the L4-5 level deeper underneath the iliac crest and make it difficult to access. I typically will try to do L4-5 first, and then here we're doing stimulation just to make sure that we don't have a problem with the lumbar plexus, and then we drop a K-wire into the disc space using dilator way up, and then you know, we keep checking with neuro monitoring on the way in. Wang likes to just use the intraoperative monitoring from the stimulation of the probes. I actually also supplement this with potential monitoring with our monitoring team at UCSF as well have suspenders to make sure that we're not injuring the lumbar plexus on these cases, is my goal there. So once we have the retractor arm hooked up here, then we're going to be ready to do the discectomy and to take a look around. And, so then we'll open the retractor a little bit, and then you'll see the view down the tube. And I think to get this view down the tube, that we're about to show you, we pulled an endoscope so that we can show you typically. I would just do this under of course, direct visualization, just looking down the tube myself. But to give you a view, we did drop an endoscope here, and took a peek around. So taking out the dilators, and then we leave the K-wire in there. For me I like to take a little purple marker, and I mark where that K-wire was, once I open the retractor and put the K-wire, so that I can orient myself 'cause I don't wanna end up too anteriorly or too posteriorly, and the purple marker doesn't look like you know, anything that's human in terms of tissue. So it's a nice adjunct. So once we have that view, we will then take a discectomy tool. Here's the shim going in just to hold the retractor in place, and then we'll pop the retractor open out the disc. So you can see we're centered over L4-5 here. We'll open the retractor just a little bit. Here's a shim in the disc space, and we don't wanna open it too big 'cause it'll stretch the psoas, we'll open it just enough. And this is a little tool to, you know, find the little ventral body, pull anything out of the way, and now you see the disc space coming into view here, and we cut the disc with a little scalpel and then we start taking out the disc herniation, and take out pituitaries, etc, and, we'll take it out with also , and cobbs. So it's very important to take a cobb, and we take the cobb along the interface of the disc with the end plate and get it all the way across to the contralateral annulus and pop through the contralateral annulus. So here you see the cobb going, scraping the end plate of L4, and then goes just barely through to the other side to open up the contralateral annulus so we can distract the disc space and get indirect distraction that way, and here you see us taking out the disc. So we'll do the cobb above, we'll do the cobb below, take out the disc in between, and then you know, it's a dealer's choice of what you wanna do to take out these discs. You can take out disc with you know, a box cutter, or . Here we have the cage filled with , and you know, it's put inside a slide so that it doesn't catch the end plate. And after you take the disc out, you can then deliver the cage at L4-5 here, and we'd like to get a nice long cage centered here in the midline and you know, the contralateral annulus and the ipsilateral annulus, so you can see the view there, and then this is the, you know, retractor coming out, and we just watch on the way out. So let's go to the next slide please. Next slide. So, we did that of course, the poor levels in that case. But let's let's take a look at some series of cases and see how these principles apply. So this is a patient who has, you know, a double major curve and is a physician who's still working and he's having a lot of pain related to L4-5, and he's up down for lamina stenosis there. He tried laminoforamenotomy, and he's still having radicular pain, not much back pain, but a lot of radicular pain, and he's got spondylolistheis L4-5 which is mobile as well. Overall, his balance is pretty good. His LL-PI is only off by a couple of degrees, his thoracic cobbing was not bad, and he's overall spinally pretty balanced. His SVA's normal, and he's a little bit off on his coronal SVA. So the question is what to do. He needs up/down L4-5 in his fractional curve, and so we wanted to use a TLIF here, 'cause we don't need a lot of lordosis and we want to get direct distraction. So the question is, how to apply to TLIF here. We did this TLIF awake, and so in this TLIF basically what we do, is we do a spinal anesthetic and that's a technique I learned from Mike Wang, a good friend of mine who had visited, and then you know the spinal anesthetic makes a surgery fairly quick. This is not the same patient. It was X-rays. I showed you a different patient, but similar procedure awake TLIF. And so, you know we prepped and draped, the patient gets a spinal anesthetic, and they get the mild sedative. They're placed prone, and then, we'll inject local anesthetic as well, even in spite of the spinal. And here we put , you know, stay in the a bit longer, gives you about 24 to 48 hours of pain relief. We do like to use navigation, it makes our cases fairly quick. We've gotten quick with navigation at UCSF, so here I'm aspirating some bone marrow, and, I'm using that bone marrow to mix with the graft extender for my TLIF, and I'll also mix in a local from taking the on partial laminectomy. I'm gonna do for the decompression here, and we're putting the snake arm on the table, and this is, I'm doing this with my partner, Catherine Miller, who's become very adept at this procedure. And we register up our navigated instruments, and then we bring in the C-Arm to take a spin, and we then navigate, you know, our way into doing the TLIF. And to save time, we have developed some tools to basically skip using K-wires and taps, and things you can basically make the incision go straight to screw in the system. And so that saves you several different steps. So we just mark out on the skin where the incisions are gonna be using the navigation, and we inject some , where we're gonna put those screw tracks, and then make a small incision and go ahead and just put the screws right in. So two small incisions were inside, we'll just go ahead and drop the screws right in there. So navigating the screws in. So we figured out how to do this with, you know, we have two different kinds of intraoperative CT scanners plus the 3D C-Arm as well, that gives us CT style images. So we can do with any of those tools. Once the screws are in, we're ready to you know, proceed with a TLIF. On the side of the TLIF, if it's too crowded with having all those screws in there, sometimes I'll just put one K-wire into that top is L4 on the right side right sided TLIF. And just to keep it from being crowded, drop the tube in, and then I'll bring in the operating microscope looking down the tube. And here you'll see that I took off the facet joint, and getting into the disc space. So in this picture here, this is medial, and this here is lateral. This is superior and this is inferior. So again medial here, and superior here. So you can see that this space is being distracted after taking the disc out by using interbody shaver and and put in a cage and then you can see the traversing nerve root right there. So here's a traversing nerve root, has been completely decompressed. And then we go ahead and drop that last screw there. And we drop the rods. And then we have the completed construct. So we did that for this patient, we can go to the next slide. So single level awake TLIF. Patient leaves the hospital within less than 24 hours, and you know, as a classic example of using MIS techniques. And you can see we got just a little bit of lordosis with that TLIF, enough to get the LL-PI under 10 degrees. And that gives you that direct foraminal decompression this patient used. This is a class one type of case here. Let's look at a class two type of a case. This patient has a high BMI, has had prior laminectomy in the past, and has failed conservative measures, a 68 year old person. Here's the imaging. So the patient has a 20 degree scoliosis in the upper to mid lumbar spine, and then the LL-PI is actually matched here. But the issue is that the patient's had a prior L4-5 laminectomy and so there's scar tissue here and the patient is a, you know, has a high BMI, and then on top of that, the patient has a lot of stenosis right through here, and also has that scoliosis up through here. You'll notice that there is an auto fusion here at L1-2, and there's not a fusion of L5, S1. We have levels of two three, three, four, four, five, two, three, three, four, five, all of them are stenotic, but mostly three, four, and four, five, and there's been prior there in the past. And on top of that, there's a facet joint cyst here too, and that's causing even further stenosis. So what are the options here? The option is to do an open surgery, or do an open redo operation, you could do it, you know, to fixate from L2 to L5, or L2 to pelvis, and then go digging through the scar tissue, probably would lose quite a bit of blood, and wouldn't be super fun procedure with the risk of CSF leak through the scar tissue and taking out that cyst, or you could try to do this MIS which is what I tried to do here. So here, the facet's cyst is here, that I was talking about. So, you know, that's sitting here. So, and here, I told you that the L1-2 and L5, S1 was out of use, which, you know, you can see here. So I wanted to do this case MIS. And so what I did was that, we chose to do laterals. We don't need a lot of lordosis here, we do need to do multiple levels. And lateral is nice because the of the patient will fall away from you, and you won't have to be doing a lot of deep digging through the scar tissue, if you'd like, you did, if you had to go from posterior. And so we did, L2, three, four, five MIS prepsoas, lateral navigated, fixation for this patient, and my partner Dean Chou, figured out how to use navigation for laterals to save the number of . This is a video of doing laterals, is not the same patient. It's a different patient, but demonstrates the technique. And so essentially, what we do is position the patient laterally, we then put in the navigation frame, and then we take the intraoperative CT scan span, we register up the navigation, and we mark the point on the skin where we're going to do the incision. We open the skin, and open the internal external obliques. So this is the same kind of technique I was showing you on the approach, where we use the to dissect our way into the retroperitoneum looking at the internal external oblique directly, so that if there's an ilioinguinal or any kind of nerve like that we don't injure it. So going through the internal and external oblique, until we find the retroperitoneal fat. So there you've seen retroperitoneal fat come into view, and then we slide in the retractors. Again, a little bit of direct visualization here to make sure we're not injuring any nerves. Get into the retroperitoneum, there's the peritoneum. We're just gonna go a little bit behind. We use a small little , to dissect the retroperitoneal fat and find the psoas muscle. Here's the psoas muscle coming into view. And once we see that we're gonna secure our retractors, we find the disc space, using the navigation system. We dilate the psoas muscle just like we did in the , but, actually we're putting these retractors, not , but actually prepsoas. So coming in just an anterior margin of the psoas, putting in the retractors. And then what you'll see is once we put the retractor, we're going to swing the retractor posteriorly to pull the psoas back, to give us the view to do the procedure. We try to line up this retractor parallel to the disc space using navigation. Here you see the disc space. We're using the interpretive nerve stimulator to make sure we don't have any nerves there, and I also run free running EMG and MEP on doing this, using the navigation to help you, you can find the disc, take out the disc. So similar to that lateral procedure I was showing you, and then you can see the disc space is becoming mobile now as we take more and more disc out with the , and then you know, using interbody tools to pull out the disc, and rasp etc, to wrap up the . You can see here we're navigating it. And again, a navigated cobb here. So I insert the cobb there, and then I'll lean the cobb dorsally away from me since I'm on the abdominal side in order to get perpendicular to the floor. Then we put in the template trial, and then we put in the slides, and we can deploy our cage. So the cage with bone grafting material, and we did this in multiple levels for this patient. And as you go to each successive level, the navigation is slightly off because you know, you've done in your body at the level below, but you have the basic idea, that if you're close by, you could figure it out, and then you can get multiple laterals done. Next slide. So using that technique, we did multiple laterals on her, and then we did posterior fixation MIS. You can see that's navigated as well, percutaneously fixated the dorsal side, and then took out that little facet joint cyst as well with a microscope and a tube. And we lost very little blood doing this, even though it's a, you know, redo difficult procedure, and we ended up here, you know, with a coronal cobb correction of 20 degrees, and then the LL-PI was matched before, it's matched now, and the stenosis symptoms are all gone, because we did lateral inner body approach and got indirect foraminal decompression and fixation down to the pelvis, including iliac fixation. Let me show you one more case. This is a patient who has a high sacral slope, and has a grade two, or almost grade three, essentially with a pars fracture. You can see this patient has an LL of 60, a PI of 77, so we need you know, about 10 degrees of lordosis correction here. In addition, there's up down quite severe, that you can see on the CT here. Sorry, clear that, and here, the is here. You can see that that framing is very very tight there. And this patient has a lot of back and leg pain, and here you can see the harsh fractures here. And, so this patient we wanted to treat L5, S1. So if we look at the the MIISA algorithm for five, one, we need a lordosis, we need to get a big graft at five, one, foraminal distraction. You can't do a lateral here, the only options are TLIF and ALIF. If you want lordosis, you really wanna go with the ALIF. Plus, you can just imagine doing a TLIF here, this is your angle of approach with a super crushed trying to pull that back. That won't be a fun MIS TLIF, no way. So I ended up doing a here. So again, we're at five, one, I want lordosis, so I choose the ALIF, and, this is the steps with the ALIF, to start off taking out the disc, and putting in progressively larger trials, putting in a cage in the front. And then we percutaneously fixated the back, lost very little blood doing this, very small incision, and this was the end result. You know, you can see the up/down foraminal stenosis, completely relieved here, because we have distracted the five, one interspace wide open, so now it's wide open. And the framing is very big here now. So you can just see the size of the frame in here, much bigger than where we started, and a nice reduction of the listhesis as well. There are some cases which we cannot do MIS, case of multi level posterior fusion that need you know, more than 30 degrees of LL-PI correction. This patient has a SVA of well over 15 centimeters and use LL-PI correction of like 60 degrees. These kinds of cases you try to do is gonna predict failure. We got to pull out the old hardware, we got to do an osteotomy, a PSO, VCR here. I did a VCR and this one from the back, and then we extended fixation and fusion up and down, and me and my partner like to open cases like this together. And so, you know, for these kinds of cases, we still have to do it open, not every case can be done in MIS. This would be a quote unquote, class four with the algorithm classification scheme. So, it's important to remember when you can do MIS, it's important to remember when you should do open. Not every case can be done in MIS. If you need a little bit of correction, certainly you can do MIS, even if you need moderate correction up to 30 degrees, you can certainly do MIS. But when you start needing more than that, or you have a big thoracic kyphosis, you got to resort to open techniques like this, like the PSO that's demonstrated there, or extended PSO to get even more correction by taking out not only the PSO, but also the disc above, and then fulcrum over a cage, or to do something even further like a VCR, where we you know, take out the entire body, a couple discs, and then you know, even rib heads to create, you know, reduction of kyphosis in the thoracolumbar junction, or in this case, this is a great six Schwab grade six, where it's basically multiple VCRs or 1.5 VCRs, in order to get a lot of correction, 50 degrees plus of correction. So, we can't forget our open techniques. You go to the next slide. So what I can tell you in summary is that, for L2-4, most MIS surgeons prefer lateral approaches, the lordosis gain, without an anterior longitudinal ligament is released is probably about, anywhere from five to seven degrees. If you release the anterior longitudinal ligament, you can get 10 up to 20 degrees. For L4-5, many surgeons will use a TLIF just because they don't like lateral and that much dissection in and around the psoas muscle. However, the TLIF doesn't give you a lot of lordosis. If you really want lordosis at L4-5, you're gonna do an ALIF, if you want just a little bit of lordosis, you could do a lateral, if you don't really need much lordosis, you just need up down foraminal distraction or do a TLIF. At five, one, if you really want lordosis, ALIF is your best solution. I tend to do ALIFs mostly at five, one. I don't like to do TLIFs there. We had a very small cage without much lordosis that doesn't leak up, look like I'm achieving my goals when I do that. So I'll leave you with this summary of the MIISA algorithm, and then my previous comments about the MISDEF2 algorithm, and hopefully by sharing some of these concepts with you, I will have helped you with your MIS deformity cases and the planning, in the time going forward. So I wanna thank you for your attention, and I'd like to thank Aaron for his kind invitation to share some concepts with you. And many of these algorithms that I just showed, I think they're in Neurosurgery Focus or in her , thanks.

- Beautiful work, Praveen. Really, you've been one of the pioneers in this area, and we all congratulate you for your amazing success. If I may ask, what do you see the future of minimal invasive to form any surgery? Let's say in five years and 10 years, would you let us know what your forecast is?

- I think, Aaron, that you're gonna see more and more technology, find its way into the OR. The technological solutions, at first when they come out, they seem to take more time, but as they evolve, they seem to save your time. So, you know, we used to have, you know, intraoperative CT and navigation, we got it at UCSF in the early 2000s, and you know, it wasn't really user-friendly it'll breakdown all the time. The software was glitchy, and we used to use it to store coffee cups, basically next to the OR. Now we actually use all those scanners because the technology has caught up with us and we're navigating more and more, and reducing fluoroscopy to a minimum, so that we don't radiate ourselves and our patients in the future. You know, there may be some role for robotics here too, and, you know, we're getting better with the interbody fusion materials in terms of getting implants that grow into the bone, and getting, you know, substances that can better bone formation, even in osteoporotic patients, and treating our patients pre-op with medication to treat their osteoporosis, to make sure we get a solid fusion. So you'll see complications come down, and the portfolio will open up more access to this kind of surgery, for an increasingly elderly population.

- That sounds great. Any other closing arguments you have about people who wanna try these kinds of procedures. What's the learning curve, how you should start, and what are the pitfalls?

- I think there's certainly a learning curve. Mike Wang talks about the learning curve all the time. And I would suggest you go start out, and watch somebody who's a master with this kind of stuff and see what the techniques are. For those of you who are residents you know, if you're really interested in this kind of stuff, do a fellowship, and get your hands on for a year with one of the, you know, masters who do a lot of this kind of stuff, and then you'll come out and be very well prepared. But I think at least watching people practicing in a lab setting, and discussing these cases in webinars like this, will help people to prepare for their cases, and not go in and bite off more than they can chew.

- Well said. With that, I wanna sincerely thank you for being our guest, and really congratulate your incredible career, and we look forward to hearing more and more about your amazing accomplishments.

- Thank you so much Aaron.

- Thank you.

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