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Grand Rounds-Minimally Invasive Lumbar Deformity Surgery

Praveen Mummaneni and Jean-Pierre Mobasser

August 04, 2012


- Welcome to another session of the AANS Operative Grand Rounds. Today we have Praveen Mummaneni with us from the university of California, San Francisco with the Department of Neurosurgery. Good afternoon Praveen.

- Good afternoon Jean-Pierre.

- Thanks for joining us today.

- Thanks for having me.

- Today we're going to discuss minimally invasive lumbar deformity surgery. So Praveen, why don't we go through disclosures and then we'll get on with the presentation.

- Sure, I'm a past consultant for DePuy and I do receive financial support in the form of a royalty from Quality Medical Publishers, Thieme Publishers, and DePuy.

- Okay, my disclosures are listed here, a consultant for Medtronic, Synthes, and a royalty with Innomed. So let's get right to the meat of this. Let's talk about what are the advantages for minimally invasive spinal deformity surgery?

- I think the advantages are two. We want to try to limit the complications and limit the amount of morbidity that we see, and the blood loss that we see with this kind of surgery. And hopefully that'll translate into a shorter hospital stay.

- And I think obviously it's important to point out that we're talking about adults as opposed to pediatric deformity surgery, as the complications can be a somewhat different.

- That's correct we're going to focus primarily on adult degenerative lumbar surgery for scoliosis.

- And why don't you tell us what the main risk factors you found in this multi-center review.

- So this was a multi-center review from the International Spine Study Group. It was presented at the national meeting at the AANS and currently now is in press at European Spine Journal, but basically looking at a large series of 950 some odd patients. What was found was that the complications were really significantly associated with the number of stages of surgery and were associated with the type of surgical approach. The interesting finding here was the complications were not significantly associated with the demographics of the patient, their ASA score, or their comorbidities. It was more associated with what kind of surgical approach you did and the number of stages of that approach that you did. So that really set up the case for perhaps trying to do these operations, minimally invasively, to see if we can lower the complication rate.

- What surgical approach had the highest complication rate?

- If you did an anterior and posterior operation, that essentially had the highest complication rate.

- Okay, very good. So let's run through the goals of deformity surgery and then how they apply to minimally invasive surgery.

- [Praveen] So the goals when you do adult deformity surgery for degenerative scoliosis really should be focused into restoration of balance and decompression and fusion. So if we go through this slide here, basically we want to achieve a decompression of the stenosis. You can do that with minimally invasive techniques. Can you place hardware is the next question because these patients often need a correction with, with osteotomies and so hardware can be placed. Even iliac screws can be placed minimally invasively. The next question is can you restore sagittal spinal balance? And that's really the major issue with adult deformity surgery in the lumbar spine, is to restore sagittal balance. And long-term studies show that if you restore sagittal balance, that's when you have the happy patient who has excellent clinical outcome measures. The issue with sagittal balance restoration, it's somewhat limited in what you can do in a minimally invasive fashion to restore it. And we'll explore that some more. The next issue is that you want to match the lumbar lordosis to the pelvic incidence of these patients and you want to match that within 10 degrees. And again, you may or may not be able to restore lumbar lordosis in a minimally invasive fashion. You can do it to some extent, but not as much as you can do it to an open extent. So I'll also say that's a maybe. And then the next question is going to take you a long time to do this. Initially, it will take a long time, there's learning curve to it. And then you want to make sure that if you went through this learning curve and you did all this surgery, that you can establish a successful fusion because the amount of bone graft bone exposure that you have is limited in a minimally invasive approach. And it's challenging to achieve a solid fusion. So we'll discuss all of these items.

- [Jean-Pierre] So while we're on the topic of minimally invasive deformity surgery. There are a lot of surgeons who do open deformity, who question if you're making all these incisions all the way up and down the spine. What is the benefit? As far as I understand it, the benefit is that you're not pulling all the muscles off the spine from top to bottom and blood loss, which can affect some postoperative issues. My question for you is, do you also see a lower infection rate in a minimally invasive deformity surgery?

- [Praveen] So I think those are all valid issues. I typically tend to use a midline skin incision rather than making 15 different incisions up and down the back. So I typically make a midline skin incision, then I go through the fascia with the minimally invasive instruments. And the idea is of course, to leave all that muscle and fascia window intact and not to disrupt it off the bone. When I do that, I have found that the blood loss is less, but you know there is no large prospective and randomized trial right now to show how much less. It's from our experience that it tends to be about a third of the open approach. Typically when we do it minimally invasively. And when we do have those minimally invasive approaches, because we're leaving that muscle window intact, we typically don't see a high infection rate. The infection rate has been very relatively low.

- [Jean-Pierre] And one other thing that you mentioned here at the bottom, which I think I've always struggled with is the fusion. Fusing the thoracic spine when they have coronal fossette, it's not like a lumbar spine where you can drill right down the synovium and pack the fossette with bone graft. How are you doing that?

- [Praveen] So I typically do not do minimally invasive thoracic deformity surgery for exactly that reason. If we look at some of the prior studies that have been published every time you get an interbody fusion as part of your minimally invasive fixation, the fusion rate has been relatively high. When you try to wrap up the fossette joints and pact bone into them in a minimally invasive fashion, there's been pseudarthrosis in some of the prior reports, which we'll examine. So for me, currently, what I do is I tend not to do these minimally invasive approaches above T10. I tend to do them from T10 down to S1, usually with as many levels of interbody fixation as I can do it.

- [Jean-Pierre] All right well we'll press on with this. Let's talk about the pelvic tilt, pelvic incidence and the sacral slope.

- [Praveen] Sure, so I think these are three very important parameters which deformity surgeons need to keep in mind. And I'll start with the pelvic incidence here. The pelvic incidence is measured. If you take a midpoint of the sacrum here and you draw a line to the mid point of the femoral head, that's the first line here. And then from that midpoint of the sacrum, if you take a perpendicular, that's the second line there. The angle in between is going to be the pelvic incidence. This pelvic incidence is something that you cannot change. You're born with this pelvic incidence. You have the pelvic incidence as an adult. You can't change it. And basically this pelvic incidence number needs to match your lumbar lordosis within 10%. Sorry excuse me, within 10 degrees in order to achieve appropriate spinal pelvic balance. So the pelvic incidence is a very important parameter. It cannot be changed, again it's measured from the mid point of the femoral head to the midpoint of the sacrum to a perpendicular drawn off the sacrum. Typical values range usually from 40 to 60. Pelvic tilt is something that you can change. And the way patients change this is to retrograde their pelvis to try to accommodate some of the lack of lumbar lordosis matching with the pelvic incidence by altering the pelvic tilt. And the pelvic tilt is measured from the mid point of the hip joint here from the femoral head midpoint, taking a vertical to that point and then again, drawing a line to the midpoint of the sacrum. So this is something you can vary, it's called pelvic tilt. And if you want to try to avoid having the inability to stand up straight, some patients will increase their pelvic tilt so that they can pull their sacrum back more in order to try to stand up straight. But that takes a lot of energy to do. The sacral slope is this parameter here where basically you're taking a horizontal line and you're measuring the angle of the slope of the sacrum and that's called sacral slope. And what we should remember is this formula here, the pelvic incidence is equal to the pelvic tilt, so equal to this number, plus the sacral slope. So this number, plus this number equals pelvic incidence. So this is the, the formula here, and this is the relationship of the two, because you have these perpendiculars here. They have to add up to this number.

- [Jean-Pierre] So in order to bring the relevant to this, to the people who don't do this degree of deformity work, as I know this is something that's become a bigger issue over the past two years. How do you use these numbers to plan your operations?

- [Praveen] So what I do is I typically will assess what is the number of degrees of pelvic incidence that I have? Say, for example it's 50 degrees. Then I look at the amount of lumbar lordosis that the patient has say that that's 20 degrees. So there's a 30 degree mismatch of the pelvic incidence to the lumbar lordosis. So I know if I'm going to be doing adult degenerative deformity of the lumbar spine that I need to increase the lumbar lordosis 10 to 20 degrees in order to be within 10 degrees of the pelvic incidence in that example. So if you have a 20 degree lumbar lordosis and you have a 50 degree pelvic incidence, you're gonna need a minimum of 20 extra degrees of lumbar lordosis in order to be within 10 degrees of pelvic incidence to have appropriate spinal balance.

- [Jean-Pierre] Okay, so if you achieve getting the lumbar lordosis to the number you want based off the pelvic incidence, will that make the plum line from C7 down line up the way you want it to?

- [Praveen] Typically the answer is yes. The caveat to that is if they have a large thoracic kyphosis, then the answer may be low, may be no. So basically if their thoracic kyphosis is normal, then matching their lumbar lordosis to the pelvic incidence will typically drop the sagittal plum line in the place where it should be within five centimeters of the posterior superior aspect of S1.

- [Jean-Pierre] So I think that's a very important point for people that are trying to use these for planning purposes is that they still have to check that sagittal plum line and make sure that the thoracic kyphosis is not out out of the range of norm to use this pelvic incidence to plan their lumbar procedure.

- [Praveen] That's correct.

- [Jean-Pierre] So let's keep going with this discussion on the pelvic parameters. Why don't you walk us through this?

- So here we have again, the measurement of the sacral slope, you have here a line horizontal to the floor, and you have here the slope of the sacrum. And that's typically going to be 30 to 50 degrees here. Here again, you have pelvic tilt, midpoint of the sacrum to the femoral head, to a vertical from the femoral head. And that's pelvic tilt. This is 10 to 25 degrees. This number and this number can be varied by the patient trying to lean back with their pelvis. And here you have pelvic incidence. Typical numbers are 40 to 65 degrees. This cannot be changed. This is from the mid point again of the femoral head to the mid point of the sacrum with a perpendicular drawn off the midpoint of sacrum. This is a number that cannot be varied, and this is the number that needs to match within 10 degrees to lumbar lordosis. So if you have this kind of a pelvic incidence and say it's 50 degrees, and you know you need a minimum of 40 degrees of lumbar lordosis to match that to be within 10 by that formula. Say the patient only has 20 degrees of lumbar lordosis and not 40, one thing they can do is they can try to lean back with their pelvic tilt in order to try to accommodate some of that mismatch. The problem with leaning back on your pelvic tilt in order to try to do that, is that it takes a lot of energy from the lumbosacral musculature and the pelvic musculature to do that. And so the patients will get tired and then start leaning forward after a short period of time.

- [Jean-Pierre] So while we're on this subject Praveen, cause you started to touch on it a little bit, when you're assessing these patients in clinic and they come in with back pain. How are you distinguishing back pain from sagittal imbalance, from back pain from fossette disease, degenerative disc disease, referred nerve pain. How are you distinguishing those different types of pain generators?

- [Praveen] So I think all of those probably play a role in many of these patients. So I look at the MRI scan. I see if there's stenosis there. So we take the stenosis into account. If they have radiculopathy, then look at the fossette joints on the MRI. And I make sure that the fossette joints don't look too arthritic. If I'm concerned about a particular fossette joint because it's tender when I push on it, I may have that fossette joint get injected with one of the pain management doctors to see if that alleviates some of the pinpoint pain that they have. A lot of the patients do have degenerative disc space disease with disc space collapse. So it's usually a combination of all those parameters of why they hurt. But I know that I must restore that sagittal balance in order to have them stand up straight and walk appropriately and match the pelvic incidence of lordosis. So that's all of those things are part of my evaluation of the patient. So I look at the MRI and all patients who have a deformity will come in and get a 36 inch standing full length cassette x-ray in order to measure the plum line from the sagittal balance point of view. What you can see is if you have a large pelvic incidence, you need more lordosis in order to achieve your appropriate sagittal balance. And if you have a small pelvic incidence, you don't need as much lordosis in order to achieve appropriate balance. And someone who has atypical thoracic kyphosis. So this is the difference between the two. This patient, if this was a person, needs much more lumbar lordosis, than does this patient. As the pelvic incidence of this patient is small, the pelvic incidence of this patient is big.

- [Jean-Pierre] Do you think that neurosurgeons tend to lag behind our orthopedic colleagues when it comes to this type of biomechanical data and applying it to what we do.

- [Praveen] I think the answer to that question probably is yes. I mean these parameters were really pioneered by a number of orthopedic surgeons. The French were very advanced in terms of their understanding of the sacral pelvic biomechanics. And then people who are members of the SRS are very well versed in this kind of thing. And I think it's important to understand these parameters if you're going to be treating these patients.

- [Jean-Pierre] Yeah, I also feel that neurosurgeons have made really vast strides in catching up in these departments and really, pelvic incidence has been a big issue for the past few years. But I don't feel we're lagging behind as much as we did 20 years ago when we were looking at other things with spinal stabilization.

- [Praveen] I think that's probably true.

- [Jean-Pierre] So let's talk about some of the reports out there in complications with deformity surgery.

- [Praveen] Sure. The neurosurgery focus issue from 2010 March had a number of papers devoted to minimally invasive spine deformity surgery correction. And the vast majority I think of the literature that's out there really came out of that one issue of Focus early on in 2010. There's been some subsequent reports since then, but primarily one of the larger series that's been out there and then is from Neil Anand. And he's also published in a couple of the other journals as well, but basically in 2010, he published a paper about 23 patients in whom he did adult deformity surgery using minimally invasive techniques. And the reason that I show this slide is because it's important to realize that these complications can happen for these patients, whether or not you do these operations minimally invasively, or you do them open. The minimally invasive operations have their own unique set of complications. And if you're going to do a lateral approach in order to do lateral lumbar interbody fixation and fusion with multiple cages, the thing that you do with the transpsoas approach is you dilate through the psoas muscle. A lot of these patients get transient dysesthesias in the anterior and lateral portion of the thighs. These are typically temporary. They typically do recover to normal in six weeks. But when I do these approaches, I tell the patients to expect that when they come out, they will have numbness on their thigh for some period of time when she usually will go away. Now because these transpsoas approaches are coming through the psoas muscle on occasion, you can injure the nerves that run through the psoas muscle. If you injure the lumbosacral plexus, primarily it's lumbar plexus because typically these procedures are done from L1 to five. You can have a quadriceps palsy, which is a pretty bad complication in terms of people being able to walk. They typically have to use a cane or something like that to walk, or a walker if the quadricep is out. He had two in this report here, they did recover. And then he had retrocapsular renal hematoma. This you can have because in a retroperitoneal approach, you can put pressure on the kidney and it's very small incision. So you don't have a lot of look looking around the corner of what the kidney is doing. He had one of those cerebellar hemorrhage. I don't know if that it's directly related, but a patient had that. And then screw prominence is another issue. If you leave the screw a little bit prod in a minimally invasive approach, the patients can complain with that, and you can't have screw fracture, you should have pseudarthrosis as well. So those were the complications reported in this particular paper from Neurosurgery Focus,

- [Jean-Pierre] Why don't we keep going through these? And then we'll discuss all the complications at the end.

- [Praveen] Sure. This paper is from a group in Pittsburgh and was also in the same issue of Focus. And they talked about their experience of doing lateral interbody fusions and then supplemental posterior pedicle screw fixation. And here's their list of complications here, but this is a, another problematic issue is they had a bowel perforation in this series in one patient. And that was not recognized early on I believe, so because you have such a small incision and because the patients sometimes have a rotational deformity, sometimes the rotational deformity can bring the bowel and the iliac vessels into the field without the surgeon being aware. And you can have bowel perforations, and you can also have a great vessel perforation of the iliac vein with these kinds of procedures too. And so we have to keep those things in mind that that can happen if you're not careful, or even if you are careful because these structures, which typically should not be in your way are rotated into your way. There's a number of other sort of complications here, similar to the other papers, some sensory radioculopathies, motor radioculopathies. These are typically temporary and do resolve in six weeks. They had two pleural effusions requiring chest tube placement. They had an intraoperative hemodynamic problem, a pulmonary embolism, durotomy during the posterior stage. So typical complications you might even see in open approaches as well. This is the series from the group in Tampa. And this is looking primarily at the patients from Dr. Uribe. And on this paper I think the authors made an issue more of the coronal balance and not at the sagittal balance. So because they concentrated so much on a coronal curve and made the coronal curves straight, and they did not look at so much the sagittal balance, nor did they try to match the pelvic incidence to the lumbar lordosis or look at the overall sagittal plum line. What the authors realized is that they did not restore sagittal balance in one third of the patients. So if you're not restoring sagittal balance in one-third of the patients who are having spinal deformity surgery, then you're not achieving the ideal goals of the surgery. The coronal correction is not the important parameter for long-term clinical outcomes. It's a sagittal correction that's the important outcome parameter. And so this is something that we must keep in mind if we're going to do this kind of operation, that we must correct the sagittal balance, must match the pelvic incidence to lumbar lordosis. Otherwise we're setting the patients up to potentially come back and have more surgery if they're not having good pain relief.

- [Jean-Pierre] I think along those lines, I think that you may be correct in a coronal lumbar curve for foraminal stenosis and neurologic symptoms, but you have to keep your mind on the fact that you need to be addressing the sagittal imbalance at the same time.

- [Praveen] Just assess not only a radioculopathy and foraminal decompression, which is very nicely achieved with these indirect lateral techniques indirectly achieved by expanding the foramen. You also have to keep in mind that you must restore sagittal balance in time.

- [Jean-Pierre] Well, let's move on. to your paper here.

- So this paper I worked on with Mike Wang from university of Miami, we looked at a series of approximately two dozen patients who had minimally-invasive surgery for spawn deformity. These patients typically would have a lateral lumbar interbody procedure, and then subsequently a posterior operation. As you can see here, I do a linear midline skin incision and then all the fascia is left intact and they put the hardware through the fascia, so that we don't have multiple incisions. And that's just a personal preference. We followed the patients out for about a year, and we looked at the coronal Cobb angles that did correct about 20 degrees in these cases. And whenever we get an interbody fusion, we noticed that that was solidly fused. But then if we did cases where we tried to wrap the fossette joints and not do an interbody fusion, then we start having a pseudarthrosis. And this is the reason primarily now I don't try to do this procedure above T10. I try to get an interbody at every single level because I have not consistently gotten fusion when I just wrap up the fossette joints through a little tube here, try to pack some autograft into that. And someone who's over the age of 60 typically has not been successful in my hands in a significant proportion of the cases.

- [Jean-Pierre] Since we are talking about adult deformity and obviously bone quality plays a role, is osteoporosis affecting your surgical plans when you do these.

- The patient has two standard deviations off the mean with their osteoporosis. Typically I will think about not doing such a large procedure for them, because I'm wondering if they're really going to successfully achieve a fusion. And I'm also wondering if their hardware will be solidly fixated because basically sometimes the bone feels like silly putty. And so you can put a bunch of, a number of screws into bone and it feels like jello so it's not going to stay there. And we don't want to have screw pull out and things like that. So for those patients, I try to treat their osteoporosis first before I treat their deformity.

- And one thing I think that we should mention is if you look at these complications, a lot of these complications are because these procedures are not just being done at L3 four and L4 five, but they're being done at the thoracolumbar junction in the diaphragm. And that's why we're seeing things like kidney complication or things of that nature. So I think it's important to realize that these are more difficult lateral approaches, not just the simple straightforward ones.

- The levels which are accessed most easily is L2 to four. L4 five is relatively easily accessible, but that's the location where in most of these studies that the patients had nerve deficits, either temporary or permanent, because at L4 five, the psoas muscle is thick. The nerve is sort of strategically located, right, where you want to go with your lateral approach in some of the patients. So at L4 five there's a higher rate of complication in terms of nerve problem. And then at L1 two, or T12 L1, you have the bottom of the rib cage to deal with, and you also have the diaphragm to deal with. And that's where if you get into the pleural cavity, you may end up having to have a chest tube.

- We talked about this a little bit or touched on this but it's also important to note that these patients are having multiple pain complaints and issues. And I think the discussions you have with your patients about what you can achieve in the complication rates for these kinds of procedures is very important so that they have a good understanding of what you're trying to do and what the things they may face afterwards are. Otherwise, if a patient wakes up with a weak quadricep or a significant dysesthesia, that's a relatively significant complication compared with the posterior approaches we've been doing traditionally.

- Correct, so the complications which can happen with minimally invasive surgery can be equally problematic. They just tend to be different. So it's very important to discuss with the patients what the prior reports have shown and to prepare them for the likelihood of having temporary thigh, typically sensory distribution abnormalities when they wake up and let them know that typically these things will get better. It's also important to let them know about motor deficits that could be permanent in weird cases. Or in terms of other complications that, the surrounding structures like the bowel, the iliac vessel could be injured, or the kidney, or the diaphragm requiring a chest tube. So those are all important discussions with the patient when they have their informed consent discussion with the surgeon.

- Early on there was, surgeons who were breaking the table and putting a lot of bend in order to access L4 five over the hip crest. And then it seems like some surgeons decided that all that bend was straining those nerves and pulling them taught across the psoas and across that lateral side of the body. And they've gone to putting less bend in the table so there's more laxity there so that when they retract the nerve, they have less of a nerve issue. Do you agree with that thought?

- Yeah I do agree with that thought. And actually Dr. Uribe has a very nice demonstration, which he shows at some of his talks, of a cadaver where he stretches by flexing the table and then unflexes the table and shows what happens to the lumbosacral plexus nerves. And you can really dramatically see the difference in how taught those nerves are. If you have a taught nerve and then you push against it, there's a higher chance of injuring that taught nerve. So I do subscribe to that.

- So let's move on then I guess the issues with these prior reports that we discussed.

- So I think if you look at those reports that I showed you from Neurosurgery Focus in 2010, and there's also been a couple of reports looking at a larger series of patients of a hundred plus patients written by Isaacs in 2010 Spine, and Roger's in 2011 in Spine, but the major complaint about these papers is that there's typically not much discussion of proximal junctional kyphosis. There's not much discussion of sagittal retrieval access and whether the sagittal balance is restored. There's no real discussion of the lumbar lordosis of pelvic incidence mismatch in these patients. And so all of these issues have been pointed out by members of the SRS who have all these parameters readily demonstrated in the open operations. And I think it's fair to say that we must have longer term followup with these patients. You can't just have a short one-year follow-up because some of these failures that happen can happen at year two or year three in terms of rod breakage. And you must assess the PJK and you must assess the mismatch and the sagittal balance of these patients. And without that it's unclear if these parameters are all being corrected appropriately by minimally invasive techniques. So the jury is still out as to the long-term efficacy. Short term efficacy seems reasonably good, but these patients need to be followed for a while. These are not cases where you can see them do the post-op visit and make sure the incision's good and then not have to worry about them. You need to bring these patients back for their annual x-ray checkup every year and make sure everything continues to look good.

- [Jean-Pierre] So why don't we move on to this algorithm for degenerative deformity surgery, and let's see if we can move through this quickly, but I think there's some valuable information at the end of this.

- [Praveen] Yeah, so because folks were doing a lot of minimally invasive surgery without a lot of guidance, we sat down together. We being myself, Mike Wang, Dr. Silva, Dr. Lenke, and then our fellows, Dr. Amin and Dr. Tu here at UCSF and put together an algorithm of when you should do what kind of surgery for which kind of patient with adult degenerative deformity. And what we did is basically we divided the ways that you do these operations into six categories. And these six categories were initially proposed by Silva Lenke in 2010 in Neurosurgery Focus for open surgeries. And so we modified that to make it more compatible and relevant to minimally invasive approaches. So in category number one from this algorithm, basically these patients only needed decompression, a minimally invasive decompression. In category number two, they get a decompression and a limited fusion of just a portion of their coronal curve. Typically with a posterolateral screw rod fixation or a TLIF. In category number three, they get a decompression of fixation, including the apex of the lumbar curves. In category two you don't even have to cross the apex. In category three you should cross the apex, and you again can do this posterolaterally with bone grafted with screw fixation, or you can add interbody fixation to those levels. In category number four, you do even more surgery, you decompress and fixate and fuse the curve with either the use of any of these procedures for interbody fixation of TLIF, a lateral minimally invasive procedure or an ALIF. And you typically include the full Cobb angle of the lumbar curve. In category number five, you then have to extend your fixation to the thoracic region because the patients who have thoracic hypostasis problems, they often will need osteotomies. And in category number six, they typically need again, three column osteotomies. So these two categories five and six are not ideal for minimally invasive surgery. Categories one through four in the appropriate selected patient are very amenable to minimally invasive surgery. So basically this is the kind of thinking that we now use when we see these patients in clinic to see, do they fall into categories one through four, or do they need a more typically standard open procedure if they're in category five and six? What are the criteria for getting each of these different kinds of treatments is something that we try to iron out. And in category six and in category five, typically iliac screw placement is a suggested if you're extending to S1 in order to prevent loosening of your S1 screws in order to prevent sickle insufficiency fracture. So this is the treatment level number one and two, which is the smaller treatments that you can do for these patients who have a minimally invasive potential treatments for their surgeries, basically level one, again is a decompression alone. A level two is the decompression with the limited instrumented posterolateral fusion, which does not cross the apex of the curve. So these are the smaller one and two level decompression alone are limited instrumentation surgeries. This is okay to do in patients who have stenosis, who don't have back pain as a major complaint, they often have anterior supporting osteophytes, which makes their curves more rigid. And more importantly, these cases typically do not have a mobile spine olisthesis. The patients are not kyphotic. They don't have major problems with their global imbalance and typically have relatively small Cobb angles. So for these minor deformities where the patient's primarily having neurogenic claudication, so neurogenic claudication for level one and level two. And they typically don't have back pain and they may have anterior lipping osteophytes, and they don't have any of these issues. No olisthesis no large Cobb angle problem, no kyphosis, no global imbalance for these kinds of cases you can do a relatively small surgery, minimally invasively and they tend to do well. So in the level one, which is the decompression alone, I typically will use a tubular retractor and we'll do a limited decompression. A lot of these patients, I can do a what Dr. Jane calls it the ipsi contra decompression, where an ipsilateral hemilaminotomy. And then you angulate your tube across the canal and rotate the patient on the bed. And then you can contralaterally undercut the other side as well. And again, we can do those kinds of operations in patients for decompression only who have anterior lipping osteophytes. They don't really have major mobile subluxations. They have pretty good maintained sagittal coronal balance, relatively small curve without thoracic kyphotic problems. These ones we can do minimally invasive decompression a lot.

- [Jean-Pierre] And I think it's also important to say that if a patient comes back three, six months down the road, and they're having new symptoms, progressive back pain, it's important to check x-rays and look if they've become unstable, if they had a previous deformity even if it were mild.

- Yes, I agree with that. And that's especially a problem during the minimally invasive decompression, you'd take out the fossette joint, or a significant portion of it. You could engender some difficulties with the progression of deformity if you do that. This is a case example of someone who is qualified from an MIS lab level one treatment. You have a relatively minor curve here. You have ossified posterior longitudinal ligament causing you a lot of stenosis. You can see the stenosis here on the MRI, as well as on the CAT scan. And this is one where because it's a mild curve, there's no olisthesis, relatively well-maintained spinal balance on the full length cassette x-rays which we didn't show here. But you can do a minimally invasive treatment where you'd come in and do a hemilamy. Take out that ossified flavum and then tilt across the canal and take out that part here. And you can still preserve the interspinous ligaments and spinous processes. And so here's how we typically do it. Small tubular retractor here. I like to use a microscope to visualize, and then you can see how we can clean out a couple of levels here in terms of a minimally-invasive ipsilateral and contralateral decompression from one side. And here's the post-op scan showing the hemilaminotomy that's been done. Decompression removal of that flavum and then reaching across the canal in the middle of the opposite side. And you can see the spinous processes and interspinous ligaments are all left intact for this patient's decompression. So that's a level one treatment, the level two treatment which is the decompression and posterolateral instrumented fusion typically at one or two levels usually don't even have to use an inner body graft for these. And you typically do not cross the apex of the curve, are for those patients who require more extensive decompression in terms of their fossette joints maybe having maybe a very arthritic and causing a lot of pyramidal stenosis. So you have to resect some other fossette joints. These patients may have some minimal back pain, but typically again, they have a minor curve. They don't have anterior osteophytes. They don't have big subluxations. They don't have thoracic hyper kyphosis that relatively well balanced. And you can do a small fusion here, one or two levels, posterolaterally, not even crossing the apex of the curve. And the reason to do the fixation and fusion is typically because you're taking out a lot of their fosette joint due to fragmental stenosis created by the cassettes. So this is a, go back one. This is a candidate for a level two operation. You have a curve less than 30 degrees, relatively well-maintained sagittal balance, relatively well maintained even coronal balance. And the patient has stenosis here below the apex of the curve. And with that kind of a patient, you can do a minimally invasive approach like this and decompress and fixate and take off the fossette joints as needed at one or two levels. So then that brings us to the level three treatment. And the level three treatment, what we're doing is typically decompressing and we're fixating across the apex of the curve and we're crossing the apex of the curve but we're not instrumenting the entire curve. We may or may not use inner body fixation to do this. These patients typically do have neurogenic claudication. They do have back pain as well. So unlike level two patients who did not have back pain. They may have a spinal olisthesis which is mobile, and they may have cobbs that are more than 30 degrees of their coronal curve. But again, these patients typically do not have kyphosis. They do not have global imbalance. And because of that reason that they are capable of having a level three treatment. Where basically the apex of the curve is instrumented, you may do interbody fixation with TLIF for lateral interbody approaches. You may have because, and the reason to do the fusion across the apex, cause you have back pain associated with deformity because typically a deformity in a stenosis extends across the apex. They may have typically larger curves. They may have more than two millimeters of sublux on mobile flection extension x-rays. They don't have a lot of anterior lipping osteophytes to give them a rigidity. But they are relatively well-maintained the coronal sagittal balance. These are the patients that can have a level three treatment, which has fixation across the apex of the curve with that, including the entirety of the lumbar curve. Any questions about that before I go on to level four?

- [Jean-Pierre] No, I think the only thing that it, that I'm sort of seeing a pattern too, is you can really group sort of level one and two together, level three and four together, and then five and six to some degree.

- Yes I think that's definitely a fair statement. And two, you're decompressing so much, you're taking away some of the fosette joints, so you have to fixate them. In three and four, you're crossing the apex of the curve and four you're crossing it in a bigger way than you did for three. And you may have subluxation, you may have evidence of instability in those cases and you have to have typically longer segments that you're treating three and four. And those are both done typically with a lateral minimally invasive interbody procedure with a posterior secondary procedure. And then five and six, I typically do those open.

- [Jean-Pierre] Yeah and one thing I like about this approach is I think that it's important to remember what we're doing is we're trying to figure out what's in the best interest of the patient. Doing a level five or six patient minimally invasively, just to say I can do this isn't necessarily in the patient's best interest.

- [Praveen] Yeah there are very few people who have a lot of experience who may try level five and six treatments in a minimally invasive way. I don't think currently that that's reproducible. I think that for those who do it, it probably does take them a long time to do. So are there some people who will push the envelope and try that? I think yes. Is it reproducible? Probably not. I tend not to do it myself. So going on to the level four treatment. The level four treatment is an anterior and posterior fixation of lumbar spine in patients who have typically severe stenosis, multiple levels, who do have back pain may have some sagittal imbalance also. Typically less than five to seven centimeters of sagittal imbalance. Anteriorly a lateral minimally invasive approach is performed, that helps to typically restore lumbar lordosis to some extent. And it does provide indirect decompression of the foramen by distracting the foramen open. Because you're providing anterior interbody support, that helps to decrease your pseudoarthrosis rate. Typically in these cases I will not do these operations if the patients are actively smoking tobacco. I will actually make them quit tobacco and check urine nicotine before I proceed. If they have osteoporosis, I'll try to have them treat the osteoporosis before I do the surgery. Osteopenia, I still typically will operate on them, just giving them the caveat that they may get a sooner arthrosis. Typically for these anterior approaches and these level four treatments you use MIS lateral techniques in order to access and instrument anywhere from L1 to L5. And again, radiographically these patients may have subluxations which are mobile. But still, they don't have the thoracic hyperkyphosis and they typically don't have rigid anterior osteophytes which are going to help them to maintain stability. So for those patients, they get a level four treatment and level four treatment typically looks like this. Interbody grafts placed laterally minimally invasively and then posterior screw rod fixation, sometimes with a TLIF down the bottom because you cannot reach L5 S1 with the lateral minimally invasive approach because the pelvis is in the way. So you have to add a tube up to the bottom. If you want to try to maintain a sagittal imbalance and fixate and fuse L5 S1. So this is a typical example of a case that we did that on, a 65 year old who has back pain and radicular leg pain. And this patient came for surgical attention. Here we see that there is some sagittal imbalance, it's approximately I would say seven centimeters off in terms of from the back of the L5 S1 to the plum line, there is some mild coronal imbalance here too. Dynamic x-rays are done as well. There's some mild subluxation here as well. We actually measured the SBA 4.3 centimeters, lumbar lordosis at 27 degrees and note that this pelvic incidence is a lot more than 27 degrees. So this patient needs a lot more lumbar lordosis. Here's the MRI scan. Every single disc space is collapsed at L5, L4, L3, L2. So L2 has one disc space collapse with foraminal stenosis at multiple levels. There's three four and four five. And then if I ask you a question, where would you treat this person? This is a stage one or level one treatment MIS LAT number one. That's not going to accomplish all our goals here. We have multiple levels, including the apex of the curve, which has to stenosis including underneath the fosette joint. This again is a level one treatment not going to be ideal here. This is a level two treatment, instrumented limited posterior fixation, but that's not going to cross the apex of the curve. You certainly can do D or E for these patients. And I don't think you're going to need a PSO for this patient because the flat back and the kyphosis is not bad enough to warrant a three column osteotomy. So what we did was a first stage surgery, minimally invasive L2 to five fixation, and then a second stage surgery with a minimally invasive L2 S1 pedicle screw fixation with a right iliac screw placement as well. And so it ended up, this is the coronal pre-op. Here's a coronal post-op. Here's a sagittal pre-op, here's a sagittal postop. So some restoration of lumbar lordosis. You can see this lordosis now is more closely going to approximate your pelvic incidence than it did beforehand. And the sagittal balance is relatively well restored, whereas here you're measuring it about four centimeters forward. So that is a typical level for treatment, which I think is a very nice way to treat this patient who otherwise might be treated with an open approach with very nice long-term results but in the short-term, this patient may lose less blood and have less morbidity.

- It looks very nice. Let me ask you a couple of questions on this. What about doing multilevel TLIFs as opposed to a lateral approach?

- That is definitely an option. I have patients who've had extensive anterior retroperitoneal surgery for other reasons. I typically will use multi-level TLIFs. It has been my experience though, that I can do a multi-level lateral approaches more quickly than I can do multi-level TLIFs.

- Yeah and I think that's a common thought amongst a lot of surgeons doing this across the country as they. That's one of the values of the lateral approach is that you have your exposure and can really get three inter body levels done almost at the time you could do one or one and a half TLIFs.

- I think that's probably fair.

- Yeah. Are you leaving your iliac screws in after fusion or are you removing those?

- I typically do not remove them as you can see here, I really recessed the head very low. I don't leave it up high. When you leave it up high that's when the patients have prominence issues and it bothers them. By bearing it down low into the PSIS, which is what I do, I haven't had to take them out. And usually even one iliac screw is adequate to try to prevent you from getting a cerebral insufficiency fracture and backing up these S1 screws. You don't necessarily have to have two although two is better biomechanically. You can limit the amount of iliac pain by putting in one.

- Are you having trouble getting that rod to match up to the iliac screw in a minimally invasive fashion?

- It can be a bit difficult. Now typically what I do is a linear midline skin incision. And by putting these screws in these, these screws are basically placed through the Wiltse plane, through the fascia. This screw I'll make a small opening and use a gear shift to get down it. And then typically by opening the Wiltse plane between S1, down to the pelvis, I usually can drop the rod right into the screw head. So I don't put a screw extension on this one. So this we just saw on that last image, we'll go onto the level five treatment now. The level of five treatment is an extension of the fusion of the thoracic spine for patients who have a thoracic hyperkyphosis. These patients may have a flexible imbalance. These typically will require a long segment fixation like this. I don't usually do these operations minimally invasively because my experience has been they get pseudoarthrosis in here. Because I'm not able to successfully establish enough bone graft on these coronal fossette joints and thoracic spine to have them adequately fused, especially in an adult who's age over 60. And I don't want to have to, I have to come back and do it over again. So these cases, if I have to go T2, I'm going to be doing them open.

- [Jean-Pierre] It seems that with our advances in technique surgical instruments, tools that we have, that the age that we're doing these procedures in seems to keep going up. I know that there are several surgeons out in California that are doing these types of procedure in people around the age of 80. Are you seeing that occur at your hospital?

- I tend to shy away from folks who are 80 plus years old because they typically have severe osteoporosis. I do do these operations on folks over the age of 70. I used to, maybe five seven years ago, I wouldn't really try any patients over the age of 65 then I migrated up to 67, now I'm up to sort of young seventies but the patients tend to live longer. And you know, it's not just purely the age either. If they come into the office and they say they're 74 years old but that they have a constitution, it looks like someone who's 60 years old and playing golf and they're active, some are still working. It's hard to turn that patient down if they're constitutionally in good shape, without a lot of medical co-morbidities. So I look at you know, what's the patient's bone quality? What's their age? How active are they? And you know, the comorbidities before I decide whether or not to do it. I usually personally tend to shy away from the 80 plus age group just because of the osteoporosis.

- [Jean-Pierre] Well we'll see if that level changes in another five years.

- [Praveen] Patients start living to 100 and then they have to reassess.

- [Jean-Pierre] Yeah. So I think you covered this fairly well. Let's move on to level six.

- [Praveen] So a level six is someone who needs a three column osteotomy to correct their spinal imbalance. So they need 30 or 40 degrees of lumbar lordosis. It's difficult to achieve that in a minimally invasive fashion. I usually get about maybe five degrees or so of correction from a lateral minimally invasive cage placement. So for these cases, I typically will do a three column osteotomy and typically we'll do the operation open and then make sure that I decompress the nerve roots, because if you do it minimally invasively, you don't get enough decompression. When you close down your osteotomy, you can create an iatrogenic foraminal stenosis, or an iatrogenic canal stenosis. And this starts to dig into the canal. So I typically will do these cases open and not try to do them in a minimally invasive way. And you know you can try to, some people talk about, try to remove the anterior longitudinal ligament, minimally invasively, and then put in multiple interbody grafts and do a posterior Smith Peterson osteotomy. In my hands, I don't like that approach. I'm nervous about opening the inter longitudinal ligament. The iliac vessels are sitting right in front there. So I think this is an approach that very relatively few surgeons can do reproducibly. And I tend not to do this. I tend to do these operations open with a pedicle subtraction osteotomy, if I really need 30 or 40 degrees of correction, lumbar lordosis to restore balance and restore my lumbar lordosis to pelvic incidence mismatch. So this is a case example of someone who had a type six treatment. This is a patient who's had multiple lumbar fusions. He's had a fusion currently. This is three, here's four, here's five, here's S1. He had a fusion of four five S1, and then he had a fusion up to three, and they took the old hardware out. And he's got this hardware here now, but he still has quite a bit of back pain. So he is radiographically worked up by folks outside of UCSF and then ultimately sent over. But you can look at his lumbar lordosis and his outside surgeons told him, your lumbar lordosis looks reasonable and you have a nice solid fusion at 3, 4, 5, and S1 is all solid. So we don't know why you're hurting is what they told the patient. And so he also got a monogram and the monogram reveals that he's got a relatively large spinal canal here. There's no real stenosis here. And again he saw the fused from three down to S1 confirmed on the CT. And again it was told to the patient that we don't think we can help you. So the question became, why is this patient having so much difficulty? And he was really went from someone who was working to someone who had trouble sitting and standing for any long period of time. And so this is the one x-ray that no one ever did for him. So he came to me and I said well, let's get a 36 inch long cassette x-ray and you can see he's got quite a thoracic hyperkyphosis here. And he relatively has a lumbar flat back though, that short segment x-ray looked like he had lordosis that was maintained, it wasn't enough. And the reason why his other surgeons didn't pick this up is because when he walks, he bends his knees and he bends his knees so that he can kind of look at you in the face when you're talking to him. But when I had him lock his knees, this is as straight as he can stand. And so he'll fool you until you lock his knees and do that 36-inch long standing cassette x-ray in order to figure out what the real problem is here. And then the question becomes what's his lumbar lordosis to pelvic incidence mismatch. So here is his pelvic incidence. Here's his femoral head here, and here's his femoral head here. In this case, the two femoral heads didn't line up perfectly on the x-ray. So when they don't line up perfectly on the x-ray, you draw a line from the middle of this femoral head to the middle of this femoral head and choose the midpoint as your femoral head, where it would be if they overlapped. So if we choose that point there and we drop it perpendicular to the sacrum midpoint and then we measure this, this is the pelvic incidence. You can see his pelvic incidence is really quite large. His lumbar lordosis is nowhere near the amount of pelvic incidence that he has. He's not within 10 degrees in any way, shape or form. And so what he needed was a level six treatment with an osteotomy and we did extend them even a thoracic spine in order to reconnect his sagittal imbalance. And since we've done this operation, now he can walk distances, he can sit, he can stand, and he's relatively much better off than he was in this position here. And that's an operation that I don't think we can do in a minimally invasive way. That's an operation that I did open, and I thought that's what he needed because in order to get a solid fusion up here by placement of bone graft on the cassettes, I needed to open up this tissue in order to get a three column osteotomy here, I needed to really expose this area.

- [Jean-Pierre] What percentage of these patients are coming to you and giving you a history that sounds like sagittal imbalance, back pain versus other types of back pain?

- [Praveen] I think most of these patients that I do these procedures on have had one and two level lumbar surgeries in the past. And then when they they're told, sometimes they have a quote unquote, a failed back syndrome and they show up in my clinic. And then what I really find is that they have a lumbar lordosis to pelvic incidence mismatch. And though they do have some lumbar lordosis, typically not enough for them to stand up straight and re-establish their spinal balance. And so then what they're doing is they're doing pelvic tilt, increasing it in order to try to stand up straight, they get tired doing that. And so they can do it for about sort of until lunchtime then in the afternoon, they're all bent forward is typically what they're telling me. And when I look at their parameters, this is what I find.

- [Jean-Pierre] Yeah.

- [Praveen] So this is basically, which you alluded to earlier, when I consider doing minimally invasive lumbar deformity surgery. Decompression alone or decompression with a small instrumented fusion in patients who don't have back pain with a relatively minor curve who don't have much imbalance. Then we can lump these two together, decompression and fusion of the apex of the curve or the full curve. Typically these can be done with lateral, minimally invasive approaches as part of the operation. And that's for patients who need more than just a simple small decompression. These patients typically have back pain, typically have a spinal olisthesis, which is mobile. And some evidence of instability and maybe in level four, some mild spinal imbalance. Here's cases where I typically don't do minimally invasively extension to T3 cases or cases that need a three column osteotomy for major deformity correction. I still think that these currently are better done open and tend not to do the minimally invasive way. And I think there's a few people who may try these, but I wouldn't say that that's reproducible. Not too far. So I think the minimally invasive approaches are not ideal for patients who need class five and six treatments, cobbs that are really big, apical rotations, big lateral olisthesis cases that typically require PSOs to correct major sagittal imbalance. These are characteristics that predict failure and probably these cases should be done in an open fashion as this one was. And so this is the essential algorithm here. You know most of these cases do come to light to the neurosurgeon because neurogenic claudication radioculopathy says typically a yes for everybody, then the question is do they have back pain? If they do not have back pain and they typically, their SVA is normal and that's why they don't have back pain. They have good sagittal balance. They may have a little bit of sublux, but usually less than two millimeters on dynamic x-rays and they may have rigid anterior osteophytes. So they can probably treat it and be treated with a minimally invasive decompression alone or with a decompression and a one or two level instrument of posterior fusion, if you need to take out their fossette joints. So that's the one and two treatment category folks. Now, if they have back pain, then the question is, do they have a spinal olisthesis? And is it a major spinal olisthesis either coronally or in the lateral plane? And do they have large cobb angles? And if they do not have big spinal olisthesis and they have some collapsed disc spaces, you may try to do a small grade two treatment of just one or two levels, or you may choose a grade three treatment where you do a lateral minimally invasive approach at the apex of the curve, because they have stenosis at the apex of the curve but you don't cover the entire curve and you could end up here. Now, if they have coronal cobb angles, more than 30 degrees with a lot of lateral olisthesis or a dynamic instability on flexion extension x-rays, then they typically will have a lumbar kyphosis. If they have a kyphosis and it's relatively mild and their pelvic incidence is not large, you may be able to do a level three treatment because they're within 10 degrees of their pelvic incidence and just fixate the apex of the curve. But if they have a large kyphosis with sagittal imbalance, the question is how big is the sagittal imbalance? The sagittal imbalance is relatively minor at four or five centimeters. You probably can do a level four treatment. You fixate and fuse the entire curve of lumbar spine. You do multiple lateral interbody approaches and you end up with a minimally invasive level four treatment. But if they need any major correction of their SBA and they have a stiff use deformity with thoracic hyperkyphosis, they either get a level five treatment with extension of thoracic spine, or an open osteotomy three column. And these two I typically don't do minimally invasively. Any questions with that.

- No, I think it's nice. It sort of sums up what we've sort of walked through over the past hour with the thought process. It's a busy slide, but I think it does show us how to work your way through that topic. I think this has been very helpful. I think that this is a good information. I think for neurosurgeons, this is really what we need to move towards understanding. And I think there's obviously some specialized centers across the country that really have achieved this level of understanding. But I think that neurosurgery needs to move towards this and understand this as well as our orthopedic colleagues do so that we can offer these services to our patients as well.

- I agree.

- Absolutely. Well Praveen, thank you so much for sharing your thoughts today. I found this very insightful and very helpful for me and sort of stratifying and having an algorithm to think my way through these patients.

- Everything that we just talked about is now in the Scoliosis Research Societies electronic textbook, which is free online to anybody who logs on to their website.

- Right. Well, it is now 5:30 on a Friday. I think it's time to go home and get a drink.

- Thank you so much.

- All right, have a good day.

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