Hello everyone, my name is Lou Tumey-Allen from Phoenix, Arizona. While we cannot meet in person for this WNS, I hope that some of these virtual presentations do fill a void. I just saw a wonderful presentation by Nick Theodore using robotic surgery for the TLIF and another virtual reality, augmented reality presentation by Dan Shuba. Two great presentations that are definitely worth looking at. This is my presentation on the topic is new and evolving technologies for minimally invasive lumbar disc surgery. But the topic that I picked may not be novel, but I'm trying to look at this from copying a page from our endoscopic colleagues. I know when I talk with Mike Wang, who is a wizard with an endoscope, and some of my endoscopic colleagues, I look at their bag of tricks and I wonder how much of that we can transfer into using our minimal access ports to accomplish some of the same goals. And so these are a couple topics that I try and explore in this presentation. These are my disclosures which have nothing to do with this this talk. The first topic I'd like to discuss is the caspar ratio. We know that the benefit of minimally invasive surgery is the fact that a smaller incision and a more efficient exposure is going to result in less discomfort for the patient. Obviously we need to have the necessary exposure to get the operation done, and so it is very important that the exposure match what the surgical target is. But as we become more facile with these minimal access ports, we can achieve a caspar ratio of one-to-one. Now why do I call this caspar ratio? A publication years ago that Caspar, the same Caspar who gave us the Caspar pinpost distractors for the cervical spine, admonished us to be mindful of the exposures that we achieve, that we undertake in order to take care of a surgical disease. And he was very concerned with the exposure for microdiscectomy specifically. And so when I look at this and I think of the far lateral microdiscectomy, I really think that this is the natural fit for the caspar ratio. And also again, new and evolving technologies is the theme. How can we get this done with stealing a page from our endoscopic colleagues? Now this is an illustration of the caspar ratio. When we look at this illustration, this is an illustration from Joseph Maroon when he described the far lateral microdisc. And this is circa 1996, obviously predating our minimal access ports. But you can see the exposure that is being accomplished in order to do a far lateral microdisc, the wiltsy approach as we call it. And then in a focusing on the actual relevant anatomy, what we would call the surgical target, I would say is marked by this blue ring. In order to do this procedure, this is all that we need to be able to get the operation done safely. However, the exposure is marked by this purple ring. And so that is a ratio that we would consider unfavorable when we put it in the framework of a caspar ratio. And so again, we're trying to adhere to a ideal ratio of a surgical target to surgical exposure of one-to-one. There is a tenet of minimally invasive spine surgery. Now when you introduce the endoscope, all of a sudden you become that ratio. Really, you flip that on its head incredibly well because the target remains unchanged. We'll define that here in a second. But the surgical exposure is significant even less, eight millimeters or so. Now the anatomical basis, which I think is fundamental to proceeding with the far lateral microdiscectomy, is first and foremost defining the foramen. And as we see in this exploded version of the neuroforamen, we can see the contributions from the rostral segment. Let's just call this segment L4-5. And so the inferior aspect of the pedicle of L4, the pars interticulars, the anterior aspect of the pars, the posterior aspect of the reticular body, contribute to the roof of the foramen. And the floor of the foramen is the superior aspect of the pedicle of L5, in this case, and the superior articular process, the lateral aspect of the superior articular process. And the disc extrusion obviously is what compromises that neuroforamen. But an understanding there allows us to begin to look at how it is that we can tackle this. And again, one of the things that was brought up is an endoscopic approach, which is a wonderful way, especially for a far lateral. When we look at the dimensions that are of the greatest interest when we're thinking about the surgical target, defining that surgical target, is the distance from the inferior aspect of the pedicle of the rostral segment to the superior aspect of the caudal pedicle. And understanding that, that is the purpose of this slide, which is the dimensions that we were able to measure out from a computer-generated model of the lumbar spine, where we measured all of the inter-particular distances within the foramen and generated these values. You can see greatest at L1-2 and L2-3, similar at L3-4 and L4-5, and smallest at L5-S1. Obviously, that has to do all with the lordosis of the lumbar spine. As the lordosis increases, the foramen is going to decrease. The pedicles are going to encroach on one another. Thus, that's the very nature of lordosis. But that also constrains the corridor, making the L5-S1 far lateral microdisc the most challenging of the procedures to do. When we look at the foramen from this vantage point, it is that understanding of where the nerve root is relative to the disc, from a posterior standpoint, that allows us to get this procedure done safely and efficiently. This is not the vantage point that we get at surgery, and so the surgical exposure is as follows. There is the anatomy at L3. You can see the PARs is narrower at L3 than it will be at L5. The distance from the inferior aspect of the pedicle of L3 to the superior ticular process is 10 millimeters, giving us a sense of what we have to expose, what we have to see, to be able to do this procedure. At L4, you have about 7.9. These are measurements from Rulin, another manuscript circa 1996, which is a wonderful manuscript to review for the anatomy of the far lateral recess. Hematigously dissected, measured, all of these dimensions that are actually directly relevant for a minimal access port. At L5, again, the constraints are the iliac crest, the alar wing, all which can constrain a already constrained corridor, or the pedicle of L5. The inferior aspect of the pedicle of L5 to the superior ticular process of L5 is a meager five millimeters. So, here we are with the relevant, what we're going to define as the surgical target. I would suggest that at a maximum, the surgical target is a 16 millimeter by 16 millimeter. But, as you will see in the exposures that I have in the upcoming part of the presentation, we can narrow that down to a 14 millimeter and, dare I say, even 12. A 12 millimeter access port, to my knowledge, is not out there. But, now we are approaching what our endoscopic colleagues are able to achieve through 8 millimeter ports. And, the advantage would be the need for only one port, although not all endoscopy is done with biportal endoscopy. So, this is the exposure of a 16 millimeter. Now, can we narrow that down even further? I would suggest that we need to see the nerve root, the lateral aspect of the PARs in the disc, how much of that superior ticular process, depending on the disc extrusion, that is the variability of the exposure. But, for this purposes of this presentation, 16 millimeters is what I'm going to be working through. The operating room setup. We need a Jackson table and, atop the Jackson's table, is going to be a Wilson frame. And then, we need a fluoroscopic unit with the image intensifier opposite to the side of the symptoms and the microscope on the same side of the symptoms. And, a lot of individuals say that they do minimally invasive surgery just fine with loops and a headlight. I prefer the microscope. Again, when we're working down a 14 millimeter access port, every millimeter with magnification illumination is incredibly valuable. Now, planning the incision, I think, is an area to spend some time on. The incision is, at times, in technique papers, not a very well defined entity. I would like to be very crystal clear on how I plan these incisions. At L4-5 and L3-4, I'll go a full 4 centimeters. At L2-3, I'll go about 3 centimeters at L1-2, which is a rare occurrence, but present. At L1-2, I will use about a 2.5 centimeter because the PARs becomes increasingly narrow. There, it gives you the superimposed anatomy over top of the skin, the ghosted spine beneath. This is what I'm palpating. I put my knuckle into the interspinous process space so I can feel where that is, and I use the crest to guide me to L4-5. And then, I plan my incision 4 centimeters lateral for a distance of 18 millimeters for a 16 millimeter access port. And there, you see, with very specific detail, the size of the incision and relative to the midline. Then, where I target the spinal needle, aiming at this inferior articular process so that I am not trying to blindly pass a spinal needle onto the PARs interticularis, which I would say is a... I would not recommend that process. With the spinal needle onto the inferior articular process, that's a reliable target. It's also very shallow, not very deep. And then, from there, we can use that same trajectory at first, but then in a sweeping motion, which is illustrated by the following image, docking onto that inferior articular process and then sweeping safely onto the lateral aspect of the PARs and then allowing that dilator to fall off the PARs and almost into the foramen. So, you get a sense. Now, I'm reconstructing the anatomy at depth and I have the ability to know I'm reconstructing the anatomy before I've even laid eyes on it. This is one advantage of minimally invasive approach and that sounding the anatomy, that tactile feel, provides us with what we can't see visually, we can recreate in our mind with a tactile feedback. And it's a component, along with the fluoroscopy and a limited field of view, that allows us to stay oriented. And here is a lateral fluoroscopic image of a 16 millimeter access port over top of the foramen. You can see that relative to the disc, it's actually above the disc, it's focusing from the inferior aspect of the pedicle down where the nerve root and the disc extrusion can be expected to be. If we were to translate that image into an illustration, it would look like this. And there you have the minimal access port, which is going to be displaced posteriorly because of the inferior articular process not allowing for an ideal configuration up against the pars. Again, the smaller this access port is, the closer it can get to the pars. But in this case, a 16 millimeter does displace you posteriorly. A 14 millimeter gets you closer and a 12 millimeter would almost be ideal. And there you have the convergence that when the table is rotated, puts you in the axial plane of the compression of the nerve root in an ideal ergonomic position. And there you see it at the time of surgery with a converging minimal access port. Now, what I call an on-foss view or an on or an owl's eye view, which is down the view of the pedicle, that's almost essential. And I really want to make sure that I am completely in line with the pedicle because the pedicle is the north star of this operation, especially as that minimal access port gets smaller and smaller. And again, I'm entertaining the notion of 12 millimeters for this. It needs to be perfectly beneath the pedicle so you can palpate the pedicle, identify the nerve root, and be able to safely mobilize the nerve root to retrieve the disc extrusion. In the operating room, the rest of the team sees the image I just showed you. We, as minimally invasive spinal surgeons, will see this image. This image is one of a superimposing the anatomy. We know the anatomy at depth. We've sounded the anatomy. This is what we've reconstructed in our mind's eye. And then when we peer down the access port as the operating microscope comes into view, we are looking at this in our minds, but we obviously do not see that. Instead, what we see is this. And we have got to make heads to tails of this. By convention, the stem is always at the 12 o'clock position, which I call the surgical position, but it's always pointing toward the spinous process. And so that helps me keep oriented. And so the pedicle will be at three o'clock. The nerve root is going outward towards six o'clock. The superior ticular process is at nine o'clock. And then the thecal sac dura, it's going to all be medial, and that's at twelve o'clock. And so obviously this is what we're going to see because of the uneven topography of the posterior lateral spine. And so we now are challenged with working with this. And we have to expose this. And so that exposure is accomplished by first and foremost getting onto the transverse process, which is a safe. You can palpate that with a forward-angled curette. And then once you can confirm bone, expose it with the Bovee cautery. Paint the lateral aspect of the PARs. And then be careful with the facet capsule. Stay away from the facet capsule. And then you have the exposure you need. This is the typical bone work that you would have to accomplish for an L4-5 far lateral microdisc. There you can see that the nerve root is ghosted beneath the intertransverse process ligament, the disc extrusion, displacing the nerve root in a rostral direction. By drilling that bone, you give yourself the ability to orient as well as the ability to mobilize the L4 nerve root in this case. At times because of a caudal migration or a migration that has not extended very rostral, the lateral disc extrusion is done by the superior particular process. And at times you do have to remove the lateral aspect. Again, caution with the facet joint. I've seen patients who will have some facet discomfort in the aftermath of a far lateral microdisc where I wanted to extend downward to ensure that I had the access to the disc base and then I see a widened facet joint. If that facet capsule is disrupted, that's a risk. And so what I do is I make sure I stay as lateral as possible. Get lateral to the superior particular process where I'm nowhere near the capsule. And this is the surgical anatomy at depth. And then this is the drilling. So here here's the process of drilling in a manner up and down on the lateral aspect of the pars reticularis. The goal here is to expose the intertransverse process ligament, which as I stated is an extension of the intertransverse of the ligamentum flabum. And then the inferior aspect of the transverse process that gives us access to the pedicle. Again, the pedicle is the north star of the operation. Here we have the, again, the ghosted anatomy. And what we want to establish is what the exposure, the sequential exposure that we're trying to achieve. Drilling down into the foramen, then using a right angle ball-tip probe to identify that north star of the operation and accomplish the exposure. And here we have the image of sweeping back and forth. And then we can see in the magenta arrows demonstrating how we're sweeping both medial and lateral to the pedicle. We've convinced ourselves we know where the pedicle resides. And from there we proceed with a complete decompression or a complete identification of that nerve root. And here we can see the action of that ball-tip probe sweeping one way and then the other, palpating the pedicle. That allows us to confirm the nerve root. And then we proceed with mobilization of that nerve root. We've identified the nerve root. We've identified the disc herniation. Now we can retract that nerve root. Here is a cubed out view of the anatomy that gives us where the pedicle resides relative to the nerve root. Obviously this is not the surgical view. Here is the surgical view that allows us to look down the access port. The bone worked on, the nerve root retracted, the disc extrusion. Now in our field of view here we can see the nerve root. Well you can't see the nerve root here. The nerve root is being retracted and the disc extrusion is right there. And then we can now retrieve that disc extrusion. And here is an example where I did not have to make an aneulotomy because I could sense by just probing that there was the disc fragment was just dangling there. And here you will see the various phases of removal of the disc extrusion with the nerve root safely retracted. Nerve roots displaced. Rostral and now fragments of the disc are retrieved. And you can see that we do not need all 16 millimeters of this exposure. And again with increased facility there's a disc, some of it, but then you know you always know by looking at that MRI that there is a sizable disc there. So there it is. And then that's the guilty culprit. Then hemostasis with cauterization, retracting the nerve root, flow seal is like magic in these small corridors where cauterization can be increasingly challenging. Then, you have the removal of the access port, hemostasis, and closure. So over the span of nine years of the series that I've been collecting, 56 cases, which averages about six a year. Some days you have efficient days in the operating room, as little as 47 minutes. Other times, you're taking the time that you need to expose that nerve root to make sure that you know what you're looking at, retracting the nerve root, and removing the disc extrusion, getting a good decompression. The VAS on a 100 millimeter scale starts at 78, goes down to about 12. In the vast majority of individuals, it can go to zero. The compression of the dorsal ganglion is incredibly painful. The length of stay is typically, these are all same day surgeries. The patient that had a length of stay of two days was a patient who came through the emergency room and already had been admitted for a day before we got to the surgery, did the surgery and they went home the following day, and so that's the two day length of stay. But the vast majority of these are done as an outpatient, they're not done as an inpatient unless they come through the emergency room and it is a same day operation. This is an operation, length of stay is measured in hours, not days. If you have a recurrence, I have endeavored upon a few revision far lateral micro discs. You have to remove more bone, you have to work through scar. The nerve root's not readily obvious, you don't have those planes of dissection. I would suggest that one of the most difficult operations that we all have to do is the revision micro discectomy to begin with. The far lateral micro discectomy is a whole different level and so I'm always cautious with that. I've gotten to the point now because of the amount of bone work that I have to remove, find virgin anatomy, safely do the operation. I believe that the transforaminal lumbar interbody fusion is probably the best direction to head for these patients instead of doing a revision far lateral. The only time I would consider a revision far lateral if it was within the past few weeks that they've had those recurrences. I've had four patients, 7% of the series has had to require a T lift, some as little as three months after the index operation, others have required that operation at up to four years after surgery. The person who had the revision T lift at three months says we should have done this at the beginning. The individual who had it at four years says that the far lateral micro disc was worthwhile. It's always difficult to tell who is going to be that one, but the vast majority of individuals, have not had any further additional surgery over my span of working with them, at least as always to my knowledge. We never know when patients move or transition or perhaps seek their care elsewhere. And the token picture of the children, I know that this presentation does not fill the void of all of us meeting, discussing, sharing experiences, listening to the pearls at the audience time and time again can provide us with, but we hope we can maybe redo that still in February of 2022 when we meet at Caesar's Palace. Please put this on your calendar. The pandemic will undoubtedly be winding down as we all begin to evolve during this pandemic and can meet safely once again, Caesar's Palace in February. We'll have more discussions like this. Thank you once again for your attention to this. I hope you found some of this valuable. I'd be delighted to have a dialogue. There's unquestionably things that I've gotten wrong in this presentation and maybe some things that you disagree with. I'd like the dialogue. Email me, send me a note, and I'd be delighted to continue the conversation in a virtual platform. And I would say that the goal, why do I put this as emerging technologies? Well, because I believe that we can do this through 12 millimeter access port. I believe that we, that our endoscopic colleagues are teaching us something with their smaller access ports. And I believe that working with them and imitating some of their techniques has a tremendous value and is another direction for minimal access ports. Thank you for your attention. I hope to see you guys soon.

minimally invasive lumbar disc surgery

Caspar ratio

minimal access ports

lumbar spine anatomy

surgical technique

pain reduction