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BackTable / MSK / Article
Genicular Nerve Ablation Procedure Technique: A Practical Guide
Thomas O'Rourke • Nov 14, 2023 • 188 hits
Genicular nerve ablation has been gaining steam in the world of non-surgical knee pain treatments. It can be an excellent option for patients with osteoarthritis, meniscus tears, and sports-related knee injuries. In patients who may need knee surgery in the near future, it does not preclude them from surgery in the way that genicular artery embolization (GAE) might. Many patients who receive genicular nerve ablation experience a significant reduction in pain. For the physician performing the nerve ablation, there are certain patient presentations, anatomical nuances, procedure techniques, and potential complications that you should pay close attention to. Dr. Smirniotopoulos shares some of his lessons learned in performing countless genicular nerve ablations, focusing especially on these topics.
This article features excerpts from the BackTable MSK Podcast. We’ve provided the highlight reel in this article, and you can listen to the full podcast below.
The BackTable MSK Brief
• Genicular nerve ablation is a non-surgical pain management option for knee pain. It is often successful in patients with varying degrees of osteoarthritis, as well as meniscus tears and certain sports-related knee injuries. Selecting patients who can adhere to post-operative physical therapy is important to enhance knee muscle strength and joint stability.
• Patients should only receive genicular nerve ablation if they experience a pain reduction of 50% or more following the administration of a nerve block.
• In patients who require bilateral genicular nerve ablation, the procedures are staggered over several weeks to aid recovery and enable physical therapy.
• For each ablation site, a motor stimulation test is conducted to ensure motor nerves are not inadvertently affected, adjusting the probe if muscle twitching is observed. The procedure requires adjustment based on real-time observations and patient responses, with particular attention to avoiding transient synovitis from ablation too close to the joint capsule, as well as preventing muscular motor defects.
• While bleeding can sometimes occur with this procedure, it can often be easily managed with thermal coagulation. Major vessels in the knee such as the popliteal artery are far enough from the nerve ablation site that the risk of damaging one of these structures is low.
Table of Contents
(1) Patient Selection for Genicular Nerve Ablation
(2) Relevant Knee Anatomy & Pain Management Considerations
(3) Probe Selection & Helpful Ablation Tips
(4) Common Complications of Genicular Nerve Ablation
Patient Selection for Genicular Nerve Ablation
Genicular nerve ablation is a versatile intervention for knee pain management. It is particularly useful for patients grappling with osteoarthritis who are either awaiting knee replacement or seeking alternative treatments. Dr. Smirniotopoulos highlights that while the ideal candidates for this procedure often have mild to moderate osteoarthritis, the clinical applications have expanded to a broader patient population. In addition to alleviating osteoarthritic pain, patients with meniscal tears and many sports-related knee injuries may benefit. Selecting patients who can adhere to post-procedure physical therapy is also crucial. Strengthening the muscles around the knee is important for patients to have positive long-term outcomes. These outcomes can be evaluated using pre-operative and post-recovery WOMAC scores and KOOS surveys to paint a picture of patients’ improvement over time.
[Dr. Michael Barazza]
To start, we've already kind of covered some of this, but what are the general indications [for genicular nerve ablation], and how do you decide who's a candidate?
[Dr. John Smirniotopoulos]
I think the best question is how do you decide who's not a candidate at this point. Because it's almost like you could do this for anyone, and that's what we see here. I think the most appropriate candidates are candidates with some degree of osteoarthritis. Now, if you look at data from the randomized control trials for this procedure, look at the sham trial for GAE, and a lot of the published data that's out there, the Kellegren-Lawrence scale is typically mild to moderate OA. We do not restrict that in clinical practice, and I'm sure other people do not restrict GAE or ablation for that.
Really, anyone who has any degree of OA, who does not want surgery, is not a medically surgical candidate yet, who has had prior surgery. It's a wide variety of patients there. The ones where you have to temper their results, and they may still want to go forward with it, are the ones who have maybe meniscal tears or recent sports-related injury. We do get those referrals certainly, and we will try the block for them. If the block works, that's fantastic, meaning that they get 50% decreased pain control, and then we'll go for the ablation. I think the biggest thing is making sure your patient that you see is going to be compliant with a physical therapy regimen after you're done.
Chances are they've tried PT and have stopped PT because they'll say it didn't do anything for them. If you can reduce their pain by half or more, then have them go back to physical therapy, because ultimately, that's what's really going to have the biggest long-term effect, strengthening the muscles around the knee joint, getting their flexibility, getting their stability. You're teaching some people how to walk again, because they've been relying on other muscles. Really getting those patients. Who not to do this on, it's almost that you leave that up to the patient, because this is such a relatively benign procedure. If they fail the block, then that's okay. They don't get the ablation.
[Dr. Michael Barazza]
Talking about the workup, you mentioned the WOMAC score. What all do you do in your workup to figure out how they're going to do and monitor their improvement after?
[Dr. John Smirniotopoulos]
When we first started this back in, I think, February is when we did our first ablation of 2022, we were just doing VAS, the visual analog score, so the scale of 0 to 10, and just saying if they got a 50% reduction of their VAS pain scale after their block, and you can do that, usually we do it 30 minutes or greater after their block itself, then they qualify in. Now, while that is how we decide who to ablate, we do collect WOMAC scores and KOOS, K-O-O-S. What we're looking for is not only, yes, pain is controlled, we want to look at the functional status.
The WOMAC is particularly good at that, because it does have a pain component in the survey, it has a stiffness component in the survey, and you may find patients complain about stiffness as their primary issue, and you think to yourself is this going to actually do anything for stiffness? Maybe not, but it somehow does because they will go to PT. Then it has a functional component to it too. We grade their WOMACs at baseline, so they'll come in for their block. I don't do it in clinic, I would do the day of their block.
We grade their block and then we grade it at follow-up. We try to follow up these patients at different intervals, and then we can see how they're improving. Now, all of this is subjective at the end of the day, so that is a component to it. We have discussed with our orthopedic colleagues of looking at range of motion, we haven't adopted that yet. Again, for us, VAS score, WOMAC, and then KOOS are the easiest surveys and by no means does anyone have to do all of them, but that's what we do in our practice.
[Dr. Michael Barazza]
Do you have any imaging that you require?
[Dr. John Smirniotopoulos]
Oftentimes, they do come in with some radiograph. However, if it's an injury like a meniscal tear or something like that, they'll probably have an MRI associated with it. I don't behold them to it, especially the self-referral patients, it may be difficult for them to bring over their imaging, and we have a discussion that yes, of course, we'll be looking at their X-ray under fluoro, we do these under fluoro in our practice. It's not a standing X-ray to really show degree of OA. However, it is appropriate that yes you can still see what's going on there.
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Relevant Knee Anatomy & Pain Management Considerations
There is an abundance of neurovascular structures located in the knee. By targeting the four major nerve trunks—supramedial, supralateral, and inframedial genicular nerves, and the variable inclusion of the suprapatellar nerve—clinicians can substantially reduce, though not completely eliminate, anterior knee pain. Before performing a nerve ablation, a nerve block is injected using fluoroscopy or ultrasound guidance to pinpoint the transition areas of bone where these nerves are located. Pain relief greater than 50% following the block indicates a nerve ablation should be performed. During the ablation procedure, anesthesia is used to manage patient discomfort. It is important to also note that bilateral genicular nerve ablations are typically spread out over weeks to ease the recovery process.
[Dr. Michael Barazza]
Your nerve block. Let's talk about the anatomy. What nerves are you targeting and where do they run?
[Dr. John Smirniotopoulos]
Probably the biggest takeaway from this is this is all based on cadaveric dissections, the whole anatomy. They've actually gone back and looked at the cadavers again as recently as two years ago and found there are more nerves than they probably initially thought. This plays into the conversation I have with a patient. We're targeting four major nerve trunks here. We're targeting the supramedial genicular nerve, supralateral, inframedial, and then the fourth nerve is the suprapatellar which some people advocate doing, some people don't.
Those are four trunks of nerves. Those are not all the nerves that are innervating the anterior compartment of the knee. I stress that to patients because I tell them your pain is not going to go to zero, I'm going to try to cut it in half, I'm targeting the major players that are here. We do this based on landmarks if you're doing it under fluoro, and what you're looking for for the suprapatellar is about 5 centimeters just midline above the patella. That is a branch that comes down off the vastus and then the idea is that it innervates the kneecap and goes into the knee joint itself.
The supramedial and supralateral, you're targeting that transition, the diaphysial transition where the femur fans out under fluoro. Then the inframedial, you're targeting that transition of the tibial plateau to the tibial shaft there. Obviously, you're not targeting the fibular branch. Foot drops are negative style points. We do this under fluoro, some people do it under ultrasound as well.
If you're doing it under ultrasound and we've done this, it's easy to do in clinic if you have that operation set up where you can bring an ultrasound machine in and you're targeting, again, that transition of the bone from a wide to narrow junction, so to speak, 50% down the width of the shaft to 60%. You're looking ideally for a neurovascular bundle. Sometimes you can actually see the genicular artery and then you're targeting around the genicular artery.
[Dr. Michael Barazza]
Don't inject in there.
[Dr. John Smirniotopoulos]
Exactly.
[Dr. Michael Barazza]
Do you take it all the way down to the bone?
[Dr. John Smirniotopoulos]
Yes. You start in your AP view. You take your needles down and you take it just adjacent to the cortex, to the periosteum. Then when you're happy with your AP view, I usually get all four needles in place. Again, those four that we talked about, I'll transition to a lateral. You're ideally having the affected knee propped up with some pillows or something so you can get the other knee out of the way on your lateral projection. Then you're going to go ahead and if you're on the bone, walk off the bone or be adjacent to the bone.
You're going to push your needles down until you're heading 50% to 60% distance. I tend to go a little bit on the deeper side, again, based on some of these cadaveric studies. Then you're going to inject your 1 to 2 cc's of local medication. We use 0.5% bupivacaine. Some people use lidocaine. The idea is you're creating a spread of a local medicine that's there, local anesthetic. You take your needles out, put band-aids on, and then you reassess them at some time point after the procedure.
[Dr. Michael Barazza]
Dr. John Smirniotopoulos, you're looking for about 50% pain relief, right, in order to proceed with the ablation?
[Dr. John Smirniotopoulos]
Exactly.
[Dr. Michael Barazza]
You don't get anybody who doesn't get that 50% pain relief?
[Dr. John Smirniotopoulos] Yes. It's rare. I actually appreciate those patients that don't because in my mind, they're not trying to convince themselves. It's like, okay, you didn't get it. That's fine. That's okay.
[Dr. Michael Barazza]
We have other things.
[Dr. John Smirniotopoulos]
Exactly. Then we start talking about GAE for those patients. I'd rather have that patient that says, didn't hit 50. Maybe I went from a 10 to an 8. I'd rather have that than someone try to convince themselves they got 50 and then you do the ablation. It's on the rare side that you don't get that 50% response. It's less than 10% of our population, certainly, but it happens.
[Dr. Michael Barazza]
So far, we've had 100% success with the nerve block. That must be really good. How long after the nerve block do you do the ablation?
[Dr. John Smirniotopoulos]
There's no time period that we need to wait, especially from an insurance standpoint because that may play in a role for an authorization. You could do it the next day. We do have some patients that schedule the block and the ablation after our clinic visit. It's more so to guarantee their spot. Then if they don't have that relief, we'll just cancel their ablation. Then if you're doing two knees, and this is probably an important feature here, I tend to block both knees in the same setting to save the patient a trip, but I separate the ablation of the knees.
The ablation of the knees, I'll separate three to four weeks. That's purely based on allowing them to recover, go to PT, get that established. Then some patients, you'll see, their pain started on their right knee. Then six months later, they're like, oh, my left knee starts hurting. They may just be compensating. If you take care of one of the knees, they may start to ease up on the other side.
[Dr. Michael Barazza]
That makes sense. For the actual treatment, do you do local anesthesia again or do you do sedation, or anesthesia?
[Dr. John Smirniotopoulos]
No, we do sedation. Especially our patient population. Sometimes, to be honest with you, with the blocks, we'll do sedation as well. I always ask a patient, how do you do with needles?
[Dr. Michael Barazza]
I wish I had asked that on my last one. The first one was super smooth. Then the next one I did, there was a lot of screaming.
[Dr. John Smirniotopoulos]
You can always tell when it's nerve block and ablation day, because sometimes the screams are heard down the hall. We're shutting down the doors in our angio room. I always have the conversation in clinic before I do anything, how do you do with needles? If they'll look at you and they'll say, needles are not my friend. Okay, let's just give a little bit of twilight, not a lot, a little bit, and then get them through the first procedure. At that point, I make the conscious decision not to ask them how their pain was right after, 30 minutes after. I'll call them the next morning. That way, guarantee that whatever was in their system has worn off or set in fentanyl.
Now, for the ablation, every one of my patients, except for, I think, two, have been with moderate or anesthesia. The patients that require anesthesia, you'll absolutely know from the block if you're giving twilight and conscious sedation and saying, this is not going to be enough for the ablation date. They just need an extra bit of support. Patients with fibromyalgia, I would just book right off the bat with anesthesia. Those are the ones that you're prepping their leg and they're already complaining of pain just from the chloroprep. It's, again, not the majority of minority, majority of ablations we do with conscious sedation, but it happens.
Probe Selection & Helpful Ablation Tips
Selecting the appropriate radiofrequency ablation (RFA) probe is critical in maximizing the treatment efficacy for genicular nerve pain. Dr. Smirniotopoulos elucidates the rationale behind using the Avanos COOLIEF-cooled RF system, highlighting its ability to create a large, uniform ablation zone, potentially encompassing some of the anatomically larger genicular nerves. Alternative methods such as cryoablation offer visualization of the ablation zone and potentially less risk to muscular structures. Moreover, conducting a motor stimulation test prior to ablation is important to avoid muscular or tendon damage. Adjustments may be made based on the stimulation results to optimize the balance between effective nerve ablation and minimizing the risk of collateral damage.
[Dr. Michael Barazza]
Let's talk about equipment. There are tons of different RFA probes of different types. You mentioned the one that you use. How do you choose an RFA probe for this and what are you looking for in terms of the type of RFA and ablation size?
[Dr. John Smirniotopoulos]
There's a lot, as you said, that's out there. There's a lot that has been studied historically out there. We use Avanos cooled RF. It's COOLIEF, that's the name, even though it's heat. The idea, similar to OsteoCool, there is some saline that's being circulated around the probe tip. It is reducing the amount of char that's formed. Therefore, it's not as self-limiting as traditional RF and you get a more uniform, about somewhere between 0.5 to 1 centimeter ball of heat to cause that ablation. It's just more uniform and more guaranteed.
If it's superior to just standard pulsed RF, that is not really worn out yet, it hasn't been studied yet, but conceptually that makes sense that you have a larger ball of heat. You're probably going to capture some of that variability of the genicular nerves based on those anatomic studies I was talking about. That's why we use it. It's also where a lot of the data has come from using that specific probe. If you trust the data, then I would go ahead and use the product that's been shown in the data to work very well. That being said, people also do cryo for this as well.
Other institutions, they'll use a cryoprobe. The thought behind the cryoprobe is you can visualize it under either ultrasound or CT. You can see your ablation zone. You may have a theoretical decreased risk of damaging any muscular structure or tendon because of that control. Again, you are using a cooled device to cause the destruction of the nerve. Plus, you're likely to get some more layering degeneration using cryo than you are heat, so that backtracking of the nerve dying. There's some argument to be used for that too.
That has its own pros and cons associated with it. If you do a lot of cryo in general, you're going to use up your argon gas. How much do the probes cost? Some of the kits that we use come in two or three-probe kits. You can go ahead and ablate three spots at once, and you're in and out of there as opposed to doing one at a time. It just really is up to your comfort. It takes a while.
[Dr. Michael Barazza]
Do you do just one spot with each needle, just burn?
[Dr. John Smirniotopoulos]
That's a really good question. That's how we started. We had those four points, and one of my partners, because I got all of us trained up to do this once the volume got too high, he likes doing the three spots, and there's data to suggest from the pain literature that four spots is superior to three spots in our own unpublished sub-analysis, that's not borne out yet. In any case, we start off with doing one probe at each location. Again, suprapatellar, the superior lateral, and supramedial genicular nerves, and inframedial. Since that cadaveric study came out and I read about it, there was also another study in the pain literature suggesting improved outcomes from doing more than those four spots.
In particular, a pullback technique for the superlateral and supramedial. It's a study that came out, I think, last year, and they had very good results. The idea, again, is that you have variability in where those nerves lie, and specifically the superior genicular nerves. They come from both the sciatic and the common femoral, and so there's just variability on the patient where that's going to go. I, myself, have been doing the pullback technique, meaning I'll go ahead, I'll ablate the suprapatellar, and I'll ablate the inframedial at the same time, so we have a two-probe kit for our purposes, two-and-a-half minutes of RF ablation, reaching 80 degrees temperature.
[Dr. Michael Barazza]
That's not bad.
[Dr. John Smirniotopoulos]
Yes, not bad. Depends on your patient. It might feel longer than it is if they're not that asleep. They'll be squeezing your nurse's hand, that's fine. You do those, then you take those probes out, and then I ablate the superomedial-superolateral at the same time. I'll go deep with it, so you're trying to get the distal tip of your RF probe about two-thirds the way down. That's because it's going to generate a ball of heat that's distal to the probe tip itself by about 4 millimeters. Some of these probes, especially the COOLIEF probe, it comes with a radiopaque marker on it.
The ablation zone starts actually a couple millimeters distal to the radiopaque marker, and then it extends beyond the tip itself. You want to get the tip about two-thirds depth, do your ablation for two-and-a-half minutes, and then pull back to about one-third depth. Repeat the ablation there. I think what's important to take away is that prior to every ablation, we do a motor stimulation test on these patients. The probes allow us to do that.
There's a actual stimulation function on the screen. You hit that, you turn it up 2 volts, and you're looking for any muscle twitching. Sometimes you'll see the probe beat on its own. That's okay. If you see the muscle twitching, it's not subtle, it's very obvious, and then you adjust. More importantly is that I repeat that test when I do the pull-back technique just to make sure I'm not hitting anything superficial that's there.
[Dr. Michael Barazza]
Do you do that with all of them, or just the superior, the motor test?
[Dr. John Smirniotopoulos]
Oh, the motor test, I do for all of them. The suprapatellar is where you definitely see it the most, in the knees. Now, we also do this procedure for the hips. I have seen it for the obturator, and we have to adjust. For the knees, the suprapatellar is where you see it the most. If you do see it for the suprapatellar, my recommendation is to adjust a little caudally, not cranially, because you're going to get off the motor neuron for the vastus, and get more on the sensory motor neuron. Now, if you go too caudal, then you start flirting with the capsule there, and you do risk ablating the capsule, and causing a transient synovitis there.
Common Complications of Genicular Nerve Ablation
A predominant concern with genicular nerve ablation is avoiding damage to the joint capsule, as its compromise can lead to complications such as transient synovitis or hemarthrosis. These complications may necessitate arthrocentesis. The importance of meticulous motor neuron monitoring cannot be stressed enough, especially around the suprapatellar region.
Even though encountering blood return in the procedure indicates proximity to the neurovascular bundle, which might theoretically aid in nerve localization, it also raises the risk of hematoma formation. Luckily, if bleeding occurs, it is manageable with thermal coagulation. While not so intimidating to interventional radiologists, physicians new to the procedural realm of pain management may be worried when they see blood. This is a relatively safe knee procedure, which maintains a safe distance from major knee vessels such as the popliteal artery.
[Dr. Michael Barazza]
Are there any other structures in the area you really need to worry about?
[Dr. John Smirniotopoulos]
The joint capsule is probably the biggest one. If you read enough of these kind of case reports that are out there, you'll see some people that have had a complication with a transient synovitis, or some type of maybe hemarthrosis. I do warn the patient that that's one of the potential risks, is having some inflammation there that may require arthrocentesis, or something of that nature. The motor neurons are absolutely the biggest concern, and frankly, I haven't seen much fasciculation, except for that suprapatellar, but I still test everything. It is the conversation I have with a patient that it is transient, it won't be permanent, but that is a potential risk factor.
[Dr. Michael Barazza]
Any other complications that you've seen frequently, or that you worry about?
[Dr. John Smirniotopoulos]
No. Occasionally, we're doing this under fluoro in our practice quite a bit. You may put in your 17 gauge trocar needle for your ablation, and you may pull that inner stylet out, and you're going to start seeing blood come back. If you do it enough, you'll see it. What that means, in my mind, and comparing this with ultrasound, is you're probably on the neurovascular bundle for the genicular nerve.
Some of the guidelines will say, put the stylet back in, adjust. I don't think you have to necessarily do that. My thought is that if you're ablating it, you're going to have some type of thermal coagulation at that point, and it might actually make you feel that you're actually close to where the nerve is a little bit more so than if you're doing it just based off markers, but you can develop a potential hematoma with that being said.
[Dr. Michael Barazza]
It's not in a challenging spot to control, I would think, and we're not talking about ablating the popliteal artery.
[Dr. John Smirniotopoulos]
Exactly. It's relatively safe. I think all of us in IR are very comfortable messing around with blood vessels. A lot of the other physicians in the country that do this maybe are not. When the reps train you, they're probably used to training those other types of physicians, and then if we see blood, we're like, I can stop this pretty easily. That's just our specialty.
Podcast Contributors
Dr. John Smirniotopoulos
Dr. John Smirniotopoulos is an assistant professor of clinical radiology in the IR department at MedStar Georgetown University and MedStar Washington Hospital Center in DC.
Dr. Michael Barraza
Dr. Michael Barraza is a practicing interventional radiologist (and all around great guy) with Radiology Associates in Baton Rouge, LA.
Cite This Podcast
BackTable, LLC (Producer). (2023, July 19). Ep. 22 – Genicular Nerve Ablation [Audio podcast]. Retrieved from https://www.backtable.com
Disclaimer: The Materials available on BackTable.com are for informational and educational purposes only and are not a substitute for the professional judgment of a healthcare professional in diagnosing and treating patients. The opinions expressed by participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable.
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