Alright, so faculty aside, can I ask which of the participants have implanted dorsal ganglion stimulators? Okay, great. So I'm happy to see that. Hopefully this will be useful. If you have questions, please let me know. I don't know if we have a simulator for dorsal ganglion, maybe not, but let's go through this. So the only disclosure I have is I'll be discussing some off label indications and we'll be using some brand names. So there really has been a void in the field of neuromodulation until dorsal ganglion stimulation was introduced a few years back. And I'll always remember, I started practicing in 2010 and the first patient that came to me was Master Sergeant T.L., who's a combat veteran, had chest wall trauma and had persistent pain in the chest wall. In fact, it was somebody very involved in DRG who sent this patient to me and we discussed what to do for the patient. And if you haven't read these two articles that came out of OHSU, one was by Justin Cetus, the first author, and one was by Ahmed Raslan, they go through destructive procedures for both non-cancer and cancer pain and talk about the level of evidence. And so this article, if I recall correctly, basically said the ganglionectomy, the evidence is fairly weak. In the longer term it's not going to be a good solution for pain. There may be some exceptions to this with a C2 ganglionectomy for occipital neuralgia, but largely that ganglionectomy I think is something that we don't use very commonly today. Nonetheless, he was having intractable pain, he had failed a stem trial, and so I took him to the operating room for a three-level ganglionectomy. He may have had some transient benefit shortly, but probably largely due to placebo-effective surgery. But with that, we decided to proceed with peripheral nerve field stimulation, so subcutaneous electrodes over where he hurt. This may have provided him also a little bit of relief, but nothing substantial. So the question comes, how do we treat focal and regional pain in somebody who has had a nerve injury? And it's not a simple question. Do we do a ganglionectomy? And I would say today this is not something that I would try as a first-line intervention. Peripheral nerve field stimulation is something that was I think more common probably in 2010, 2012, where you put subcutaneous electrodes. This was commonly used for back pain, for various pains in various parts of the body, and that's another option. Spinal cord stimulation can certainly be used also, but you're covering a broader area with spinal cord stimulation. But dorsal root ganglion stimulation has really filled a void where we can now target certain segments of the body, and especially in situations of either complex regional pain syndrome or of causalgia, pain due to a nerve injury, this has emerged as a really strong consideration for how to treat these patients. So Jennifer talked about this, but this was the first study to look at spinal cord stimulation and physical therapy compared to physical therapy alone in patients with reflex sympathetic dystrophy. Jennifer talked about the outcomes for this. And though patients improved, and as Jennifer mentioned, that in retrospect, looking back, most patients felt they had a valuable, or all patients felt they had a valuable experience with the spinal cord stimulation. You know, the longer-term patients, you could not tell a difference in the outcomes at five years out. But in the first two years, there was a very significant difference. So what are some of the limitations of spinal cord stimulation in patients that have regional pain? Historically, I think number one would have been very true. Coverage of just a painful area is difficult or impossible. And I think this was probably more true in the era when we were using paresthesia-based stimulation. So if you do a spinal cord stimulator for somebody that has right ankle pain, and you use a tonic mode of stimulation, they're going to get paresthesia of the whole leg more than likely. You're not going to be able to isolate just the area of the body that has pain. Now, if you're using paresthesia-free stimulation with burst or higher frequency stimulation, that overcomes that limitation. But historically, that would have been one consideration. The second would have been the positionality of the stimulation. So with spinal cord stimulation, there's some element of positionality. And this would be one of the limitations of this. There's some tendency to develop tolerance to the stimulation, especially in the realm of complex regional pain syndrome and peripheral nerve injury. And historically, the data wasn't superb, though this has changed. So over the last five years, I think data for, without question, data for spinal cord stimulation has improved, and particularly in the field of complex regional pain syndrome and peripheral nerve injury. So alternate targets were needed. For similarly, for peripheral nerve stimulation, what were some of the limitations? So for this patient, putting a paddle electrode over a peripheral nerve is not an insignificant operation. You can do it percutaneously using ultrasound guidance, but it's not always a trivial procedure to do. For some nerves that have mixed motor and sensory functions, motor recruitment can be an issue in terms of offering this therapy to patients. And one target nerve may not be adequate for covering the region of pain. Again, highlighting the need for an alternate target. So the dorsal reganglion, I think, has always been known as an important target for pain, but over the last ten years, the importance of this structure has grown considerably. I think largely in the basic science community, which has been translated into clinical practice. So why historically have we not known of the dorsal reganglion or thought of as a target for stimulation? I think access to the structure was perceived to be more complicated than putting in percutaneous epidural spinal cord stimulator electrodes. Different approaches were taken, either going extra foraminally or going from the spine out. I think it was felt that other targets were more relevant for the source of pain, and I think the mechanistic understanding was something that was still evolving. So dorsal reganglion has the ability to modulate the input that's coming in from the periphery in various ways. It can either stop it all together, it can block the input, it can modulate it by slowing the input of axons, or it can serve as a pass-through where the peripheral pain signals are passed through the central nervous system. And it's been shown in animal models of peripheral nerve injury that if you put electrodes into the dorsal reganglion, you can see that these neurons have higher spontaneous firing activity, and this was work done by Marshall DeVore. And then through two studies that were done at our institution by our neuroscientists and neurosurgeons, they had a very innovative study where they looked at patients that were undergoing tumor resection through vertebrectomy. So as you know, when you do a vertebrectomy, you often ligate the thoracic nerve roots, and this provides an opportunity to remove the dorsal reganglion from these patients. So historically, obviously, these were just discarded, or they were just cut and divided. But with this study, they actually took these ganglia out, and they studied them, and they found very interesting things. So first of all, voltage-gated sodium channel 1.7, which is felt to be important in the pathogenesis of chronic pain and neuropathic pain particularly, is upregulated in patients that had pain associated with compression of the dorsal reganglion as opposed to those that didn't. And the current needed to stimulate firing of these neurons was lower in patients that had neuropathic pain versus those that didn't. So with this scientific basis, the idea of stimulating the dorsal reganglion as an important target evolved, and this was the trial that was published in 2016, where neuromodulation options really expanded substantially. So this was a randomized trial comparing dorsal reganglion stimulation with spinal cord stimulation for two indications. So the first was complex regional pain syndrome, and there are very defined criteria for this that we could talk about. But the two indications were, one, complex regional pain syndrome, and secondly, costalgia, which is pain due to nerve damage. And just to highlight how the leads are placed differently, on the right would be a standard percutaneous spinal cord stimulator lead placement, where you have two leads. One is in the midline, I think in this case, and one is just eccentric to the right. On the left, this is how dorsal reganglion stimulators are placed. So you're actually placing the lead outside the foramen. You can see the electrodes are designed differently, and hopefully we have models of these to show. But whereas a typical spinal cord stimulator lead would have eight contacts, this has four contacts. It's a much finer electrode, and it's placed differently. So 152 patients were randomized for the study. 76 patients were randomized to the DRG arm. 76 patients were randomized to the spinal cord stimulator arm, and they looked at two main endpoints. One was at the three-month visit, and one was at the 12-month visit. And what they found is that there was a greater proportion of patients who achieved a 50% improvement in their pain in the DRG group versus the spinal cord stimulator group. So at three months after the procedure, this is looking at both patients that had an improvement in pain, both in the trial and the implant. So I think just over 80% or 81% of patients were doing well with DRG at three months. At 12 months, I think it went to 76% or 78%. But it also highlights that spinal cord stimulation is also a good intervention for this therapy as well. If in some instance dorsal reganglion stimulators cannot be placed, spinal cord stimulator patients will still do well, with more than 50% of patients doing well at 12 months after the trial. Now if you look at just patients who had implants only, the success rate was even higher. So at three months, 93.3% of patients had success, meaning a 50% reduction in pain at three months, and that was maintained at 86% at 12 months. So really strong and robust evidence for the use of this therapy. So the indications that I mentioned are patients with CPRS1 or CPRS2. And the common examples of this would be, or a common example of this that you might see in practice is ilioingual neuralgia due to hernia repair, knee pain due to either knee surgery, ankle pain, focal neurological pain syndromes due to a nerve injury, or complex regional pain syndrome. So this is a patient that we treated, you know, a couple, maybe a year and a half ago at our veteran's hospital. 34-year-old female, a veteran, had undergone multiple right ankle surgeries due to pain, had developed an intolerable burning foot pain, and she had really tried multiple options to control her pain. And this would have been historically a candidate for spinal cord stimulation, but we talked about some of the limitations of the therapy. Using tonics, she probably would have gotten all right leg stimulation, but para-seizure free stimulation could certainly have been an option for her. But given the focal nature of her pain, DRG, and given the level of evidence, DRG was probably a better option for her. So we trialed her with both an L4 and an L5 lead. They're relatively straightforward to place these electrodes, and putting in more than one gives you an opportunity to see which is the relevant level. There is some crosstalk between dorsal root ganglia, where if you place an L4 dorsal root ganglion stimulator, you may have coverage of both regions, cranial and caudal, to that target level. In the trial, ultimately, she had excellent pain relief with just the L5 stimulator put. So, though we've talked about the two main targets, and I believe dorsal root ganglion stimulators in America are approved for T10 and below, there are some studies looking at other indications and other ways of putting them in. So this is not something that I have done, and I would suggest that you exercise caution, but I think some of the faculty in the room have placed cervical level stimulators and upper thoracic level stimulators. But there is a growing experience with this. I think this is a study of 20 patients that came out of Germany. There were patients that had both cervical and thoracic placements, but seven patients had thoracic leads, 13 patients had cervical leads placed, and they commented on the safety and effectiveness of this therapy. One patient had a transient paresthesia of the arm at a segmental level, I think the C5 level, but that improved. But as you know, for those of you who have done cervical foraminotomies, the area is fairly tight, so it's a relatively small space, so I would just suggest that you exercise some caution if that's something that you want to explore. There's also ongoing studies of dorsal root ganglion stimulation for lower back pain. This is a series of 20 patients from the Netherlands where they had patients that were not operated, they placed L2 dorsal root ganglion stimulators bilaterally for discogenic back pain, and significant improvements were seen both in the pain scores up to 12 months afterwards, as well as in the disability indices up to 12 months afterwards. Phenomenal pain is something else that's been explored for this, and I think to have these approved in America, you have to really believe that it's peripheral causalgia that's causing the pain, which really is true for many patients that have phenomenal pain. There is an element of a peripheral nerve injury that's causing the pain. There are various ways to test whether a patient would have a response to this therapy, but it's a fairly easy therapy to try and is a good indication for that. One of the limitations of dorsal root ganglion stimulation, at least today, is that you cannot put them in percutaneously in patients that have had previous surgery. Some of the faculty, notably Steve, probably has some insight into how far they're coming along with regards to creating a paddle or a surgically implanted lead, but this was something out of Germany, two patients that underwent open placement of a dorsal root ganglion stimulator, so you can see the patient has had a previous laminotomy on one side. They intended to go in and do a foramenotomy and place the lead surgically, where they plastered out the foramen and then used a fiber and glue to create loops and place it down on the thecal sac. So some of the more common indications that you'll see in your practice today are patients with nerve injury, focal pain syndromes, post hernia player, hip pain, knee pain, post thoracotomy pain, and post mastectomy pain are two indications that you'll see as well, though these may be off-label indications, and I would exercise some caution before placing the leads in the cervical spine. So hopefully we can go through quickly just some of the technical considerations for the implant. The first would be to understand at what level you need to put the dorsal root ganglion stimulator in. Generally for a trial, I've placed at least two leads in so that you have the ability to figure out what is the most effective level, but this is just a nice slide that shows you where you think about what what levels you should target. So L4 and L5 for leg and and perhaps lower back pain though and for inguinal pain probably higher up L2 would be that the target level for that for that indication. The way you put them in is a different than traditional spinal cord stimulator. So for a traditional spinal cord stimulator, if we were, for example, placing the lead at the top of T10, this is the pedicle here. So for a spinal cord stimulator, you might start here with the needle traversing at this level where you enter the epidural space here and then you thread the lead up. For dorsal ganglion stimulation, it really is very important to have the ideal entry point of the ideal trajectory. So generally we would mark three points on the patient's spine. First would be an AP x-ray showing where you want to target the pedicle, so the target pedicle of choice. The second would be where you want to enter the epidural space and the third would be ultimately where you want to enter and so marking those three points, you can have a nice linear line where you need to go. The only exception to that would be for going out the L5 foramen, which is a little bit different. So it's going to be a little bit more angulated because you're going to start a little bit closer, enter the L5-S1 space and exit the L5 foramen. I would say that the L5-S1 is a little bit trickier, I would say, than doing it further up in the spine because you have a little bit less maneuverability and I think you have to be a little bit more careful at that level in terms of avoiding getting a wet tap. S1 is not something that I have a lot of experience with, but I know neurosurgeons do and I think along the lines of what Steve had mentioned, this is really an area, so percutaneous procedures in general, getting epidural access is something that we should be familiar with, but I think accessing S1 is another area that we as surgeons see visually, but perhaps putting a needle in is not something that we do commonly. But I think this is one area where I need to improve my practice and I would encourage you all to do the same because these are patients that can benefit from these interventions, particularly for pelvic pain and foot pain syndromes. These procedures can be done either under sedation or under general anesthesia. I would say we do more of these cases at our veterans' hospital than outside and for whatever reason at the VA we've had more success doing them asleep under general anesthesia, so either on a Wilson frame or some flame to help straighten the spine is useful. And again, I think the most important thing to have a successful outcome is to really mark where your trajectory is and pick a really proper needle insertion point. I guess that's it. So as far as one other comment on placing the leads, so once you place the leads into the spine, the other critical factor would be creating strain relief loops. Somehow I've lost a slide about that, but it's really critical. Once you have the electrode go out the foramen, you want to create two loops, one that goes superiorly and one that goes towards the foramen, and these will really help reduce migration. In our patients, we did have one patient who had leads migrate, so it can happen, but it's unusual. So I hope that was helpful. If you have any questions, I'd be happy to take them or happy to share my slides if it's useful for your practice. Any questions? No? Okay. Steve, maybe you could comment for a minute. Are there any progress on paddle electrodes for dorsal ganglions, or is that something that's a little bit down the line?

dorsal ganglion stimulation

nerve injuries

targeted pain relief

complex regional pain syndrome

implantation of dorsal ganglion stimulators