All right. Well, thank you to the course directors for inviting me to speak. It's a pleasure to be here. So these are my disclosures. So as far as lateral deformity correction is concerned, we're going to go through the approach rationale. We're going to review some anatomical points. We're going to look at access considerations and preoperative planning. We're going to look at specific different deformities and what one should think about in terms of approaching a deformity from the lateral approach. And we're going to look at some patient examples. So the sequence of lateral approaches to deformity is going to start out with having a monitoring system in place. Any lateral trans-soas deformity, this is the one time where neuromonitoring becomes quite important. And neuromonitoring is controversial in terms of its necessity in a lot of cases. And there are a lot of advocates that suggest no monitoring for nothing. But this is the one exception in spine surgery where monitoring is absolutely necessary because of the obvious presence of the lumbosacral plexus. So that's one thing that we got to be careful about. If we say neuromonitoring is not necessary, this is actually very necessary for this approach. So what are the advantages of the lateral approach? So it's potentially a muscle sparing technique. It's minimally invasive. You have the opportunity to restore the anterior column. And you can, to some degree, restore sagittal balance. All of the talks that we've had so far when we discuss the main workhorse for sagittal balance improvement, the lateral technique is not the main workhorse for this. But it does influence it to some degree. So the rationale for the direct lateral approach is really based on our exposure for routine anterior approaches. And when we talk about the lateral approach, it really is an anterior approach. But it's just an interolateral approach. And so a lot of the concept of how this technique originated really is based on our own knowledge and exposure to our standard anterior approaches. And so it can be performed with supplemental fixation or lateral plating or posterior instrumentation. Very rarely does one advocate for standalone usage of the lateral inner body cages. But as time passes, I think we may encounter certain scenarios where that may be a viable option. Because it does significantly increase the rigidity of that inner space substantially. And the additional fixation may or may not be that much of an additive benefit when it's a one-level surgery. And one of the other benefits is minimal blood loss and operative time. The lack of an approach surgeon certainly can be useful. So as far as what levels, the direct lateral approach is going to be L1 to L5. When dealing with a lumbar spine, you can actually go up higher in the thoracic spine as well. So one of the other benefits when comparing it to anterior surgery is avoiding retraction of the great vessels. And you have the opportunity for anterior load bearing for better fusion. And you have a much larger surface area for bone healing when you compare this to T-lifts or pliffs. So definitely a big advantage. So you're going to have the opportunity for a greater opportunity for an indirect decompression when you compare that to a T-lift or a pliff technique. A greater opportunity to remove a greater amount of the disc and hence get a better amount of surface area for fusion. And when doing a pliff or a T-lift, if you have a very tall disc base, that becomes less of a stable entity when you're using a pliff or a T-lift. And having that lateral cage is a lot stronger when you're dealing with a tall disc base. And you don't have to retract the neural structures with the exception of the fact that you're retracting the lumbosacral plexus. But you're not directly retracting the dura. And so as such, there's less of a chance for a CSF leak. So what are the optimal conditions for a direct lateral? This is optimally designed for L1 to L5. Sometimes L4-5 can be challenging if there's a high-riding iliac crest. If you've had a patient with multiple previous posterior surgeries where there's a lot of scar tissue, this provides you with a fresh plane to gain access to the disc space. That's one of the other potential advantages. An ideal circumstance would be someone who's had a L5-S1 fusion who needs an adjacent segment procedure or L4-S1 fusion with an adjacent segment procedure at L3-4. Sudarthroses, after a posterior fusion without inner body, this can be successfully addressed by approaching the disc space from the lateral approach. Again, you get a fresh, clean tissue plane. For patients with degenerative scoliosis, if the scoliosis is not severely imbalanced as far as the sagittal-vertical axis, you can get a very reasonable correction of scoliosis from the lateral approach when regarding coronal alignment. And also for grade 1 or grade 2 spondylolisthesis, you can get, with a distraction from the inner body, you can get a significant correction of this. And so we'll show some case examples of all of these situations. So as far as the anatomy is concerned, we're going to start out with looking at what layers you go through when you're doing the direct lateral retroperitoneal approach. So as far as which muscle layers you're going to go through, the external oblique followed by the internal oblique. Then you're going to go through the transversus abdominis muscle and then the transversalis fascia. Then at that point, you're going to be able to palpate the psoas muscle. And you also want to palpate the transverse process. So you're going to be in the retroperitoneal fat at this point. And so the neurologic structures, you have to be familiar with, as these are the very structures that we're trying to be knowledgeable about. And like Dan explained earlier, you can't really predict a sensory deficit from these approaches. So we're retracting nerve roots. A large amount of these nerve roots are sensory. When you're doing a trans-psoas approach, you're essentially splitting the muscle fibers of the psoas muscle. And along with those muscle fibers, you may be retracting against sensory nerve fibers. And the only way to really know whether or not any damage is done is to have the patient wake up and see. Fortunately, very often, these are temporary sensory losses. And very often, they're transient. But sometimes they're not. So the genitofemoral nerve involves the cremaster reflex and can also be associated with scrotal pain if it's damaged. The hypogastric sympathetic plexus can result in retrograde ejaculation. And you can also have hyperthermia reactions due to sympathetic chain damage. So this is a further schematic indicating the nerves that are in the vicinity of the psoas muscle and the potential for injury. When this technique was introduced, the incidence of weakness in femoral palsies was a lot higher. And I think as time passed and people have learned more and more about the lumbosacral plexus and have appreciated more of the anatomy of the lumbosacral plexus and the need for monitoring, the incidence of these palsies has decreased significantly. At our institution, in order to reduce the incidence of a palsy, we actually put electrodes into all four heads of the quadriceps. And this will catch more of the nuances of retraction than if one were to randomly put an electrode into one head of the quadriceps. And so that is one technical way to catch more of these retraction injuries. And so Levi et al. examined the lumbosacral plexus in cadavers and came up with a good schematic to look at the positioning of the lumbosacral plexus with respect to the disk space. And you can see as you go further down at L45, that's where the lumbosacral plexus is going to be at more risk. So looking at 118 patients from their group in 201 disk spaces that were treated, they reported a 1.7 incidence of ephemeral nerve injury. And they also reported a 4% abdominal flank bulge. Does anybody know why an abdominal flank bulge may occur? What nerve could potentially be injured from an abdominal flank that would result in an abdominal flank bulge? It's a nerve that comes out right around L1, L2. So it's the iliogastric. Yeah. So that nerve can come out right around this area. And again, it's one of those things that you're not going to be able to monitor. And damage to that nerve can result in an abdominal bulge. So looking at the success rate, you can see that the success of being able to access and treat the L45 inner space, that was the least successful. The other levels were 100% of the levels were able to be treated. And the lack of success is always due to the positioning of the lumbosacral plexus within the vicinity of the L45 disk space. So you can see that the abdominal flank bulge, again, is most common at the higher levels being fused. So L12 and L23 are the more common culprits for that problem. So important points about patient positioning. You're going to gain access to this retroperitoneal space by having the patient appropriately positioned such that the iliac crest is separated away from the bottom part of the rib cage. And you need to place this patient on a table such that you can break the table and gain that access point. And so that's the other important feature of the positioning is to make sure that this leg is flexed. And that way you have less tension within the psoas muscle itself. The reduced amount of tension within that psoas muscle is going to give you a little bit more latitude with the degree to which you can retract once you're trans-psoas. So if you have a tense psoas muscle, when you retract, you're going to be putting more pressure on the plexus than if that psoas muscle is more relaxed. So as far as patient positioning, you're going to want to put a roll at the break point in the bed. You're going to potentially use a bean bag to maintain the positioning. And so like I mentioned earlier, you want to flex that hip. And so there are a couple different ways to go about accessing the retroperitoneal space. You can either choose a two-incision approach or a one-incision approach. Initially it's advocated to start out with this two-incision approach, where you make a separate incision more posteriorly, such that you'll be able to put your finger into that retroperitoneal space and then meet up here where you make a separate incision. And you'll be able to safely determine whether or not you are avoiding the entrance to the peritoneal cavity. So by doing this way, it's a little bit safer than just making an incision out here at the very beginning. If you choose not to do the two-incision approach, I would advocate for making this incision just a little bit bigger, and that way you'll be able to see the muscle layers a little bit more readily, and almost be treating it like a mini-open approach when thinking about a general lateral, direct lateral approach to the spine as you would experience during a normal open procedure. So at this point, this is where you would put in your dilator and your neuromonitoring stimulator, such that you can check for the lumbosacral plexus and use AP and lateral fluoro to identify the proper position to dock your dilating tubes. So as is the case with any MIS procedure, your accuracy is only going to be as good as your ability to image. So it becomes increasingly important for you to have very good fluoroscopic images, and you have to strive for a perfect AP and a perfect lateral. And this is done best by rotating the table rather than the C-arm. You want to have the patient essentially perpendicular to the room. That way, the fluoro is going to be more easily managed, and there's going to be less of a fiddle factor to get perfect images. So moving on to the implants, there are a variety of different options to do this. Looking at ways to improve the amount of lordosis that you can achieve, this is a review of release of the anterior longitudinal ligament. We all have discussed that the main workhorse for the correction of sagittal deformity is the posterior approach with the osteotomy techniques. But what we often forget about is that an anterior lengthening can also be potentially an option. And this is from Juan Uribe's group in South Florida, where they discuss the release of the anterior longitudinal ligament as a means of providing increased sagittal correction. You can see, though, that, again, we're not talking about cases with huge sagittal vertebral axis numbers. These are fairly mild cases of sagittal imbalance. And so, again, even with the release of the ALL, we're aiming at trying to treat patients with relatively minimal sagittal malalignment. And so, while they had a successful result, again, we're starting out with deformities that are relatively minimal. And you can see, for this anterior-only example, the amount of alignment that is achieved in terms of the correction is primarily coronal. You can certainly get a better alignment with the inner body spacers put in laterally from the coronal perspective. Again, the focus of this article was on the coronal alignment rather than the sagittal. So what if you need more correction? Can you use this procedure in conjunction with a posterior procedure? And certainly you can. There are some people who have advocated for the lateral insertion of spacers into the disc spaces above and below the area where you would plan to do your osteotomy. In that way, you would have a stiffer construct. Very often, the site of the osteotomy is a potential source for rod failure and rod fracture. And that's due to the presence of disc material above and below the osteotomy and a potentially loose part of the spine. So increasing the rigidity of that by putting in these lateral spacers will potentially stiffen up that area where the spine could be potentially vulnerable. So I think this is a later study from Juan Uribe looking at further outcomes. And he does describe a better ability to correct the sagittal vertebral axis using this anterior release technique. And this certainly is, I think, something to consider as it may gain increased importance in the future. And when combined at multiple levels, I think multiple anterior releases combined with posterior instrumentation could potentially achieve similar correction to osteotomies. So these are just looking at some routine fluoro shots during a deformity correction. You can see how initially over here you start out with a fairly prominent coronal deformity. And the important thing as far as technique is concerned is to get into that plane within the end plate and to go all the way across and make sure you break across that osteophyte that might be present. Because without breaking across that osteophyte, you're not going to be able to distract the way you would want to and hence would get less of a correction than you would like. So make sure that you go all the way across. You want to put in cages or trials with maximal height and distraction. As you can see, as this is inserted, you get a very good correction of that previously abnormal coronal malalignment. And you can see this is another example of a very solid coronal realignment. You get a partial correction just from the anterior portion of the surgery. And in a staged manner, we go in and put in the posterior screws. This is a 74-year-old dentist who I treated, scheduled for an anterior-posterior. And he was recovering from the anterior part. And you can see he has a partial improvement of his coronal deformity. He really felt so good after this anterior correction that he refused to have the posterior part. So I think he's going to need it. This case is only about a month old, so we'll see how he does. He's going to come back and see me in clinic in another couple weeks. But originally, this was going to be a larger construct, but he's very relieved with his preoperative symptoms at this point and does not want any further surgery. So as far as other deformities, grade 1 and grade 2 spondees, a perfect application for this technique, especially if you have a patient with a spondee with a fairly decent-sized disk space and mild to moderate stenosis within the neural frame. And I think you can get a very nice inner-body graft into this disk space and have a resolution of pain and pathology. So how much of a foraminal decompression can you actually get from this indirect decompression? The answer is that you can get about a 35% area increase. And this is a study that evaluated that specific question. And so that foraminal area of 35% is significant because it provides you with significant relief of symptoms. And this was all correlated with improvement in patient pain scores. So one thing to remember is that your indirect decompression is only as good as the spine's ability to sustain that distractive force. And so if you end up having subsidence of your inner-body cage, you're going to lose the effect of your indirect decompression and end up where you started out as far as your foraminal area is concerned. And so this is a patient who I treated not too long ago who had an extensive decompression by another surgeon. And this patient developed a iatrogenic spondy. She was an 81-year-old woman and didn't want another big surgery, yet she was having a lot of pain and instability. So she had this indirect lateral fusion. And so initially her alignment was better and she had no subsidence, but you can see over time she started to subside further. She is fused, however. So she's doing better, but she's not as good as she was on post-op day one. So looking at this subsidence issue, Pimenta evaluated some of their series retrospectively and came to the conclusion that the larger the cage in terms of its lateral dimensions and AP dimensions, the smaller the incidence of subsidence. This makes perfect sense because you want to engage the outer ring of the end plate to the maximum degree. So when doing lateral inner body fusions, in order to reduce the risk of subsidence and to have a long-lasting effect of that distractive force, you really want to make sure that your cage is as long as possible from both the lateral and AP dimensions. So in the treatment of lateral deformity, there are a wide scope of options. You're really going to often, I think the best results are achieved through a combined approach when you're dealing with a lateral approach. I think the lateral approach mostly, in my opinion, is an adjunct to a posterior approach when dealing with deformity. It's only small deformities that could potentially be treated with a lateral approach on its own. But when you use it in conjunction with a posterior approach, I think you can have a very powerful means of correcting deformity. Thank you.

lateral deformity correction

lateral approach

spine surgery

muscle sparing

minimally invasive

anterior column restoration