Patient-matched Total Temporomandibular Joint Replacement with Intraoperative Real-time Navigation and Intraoperative 3D-imaging

Jana Neider Welcome to our next webinar in our craniomaxillofacial Brainlab webinar series. We are now live here in Munich from the Brainlab in Germany. It’s a pleasure for us that you are here today, especially after we had the very successful webinar two weeks with the mixed reality. We received a lot of requests from you, and I’m very happy that we have another special interesting topic for you today prepared. But before I introduce to our speaker, Dr. Zimmerer, I would like to explain a few points.

This lecture will last about 30 to 45 minutes, followed by a 15-minutes question and answer session. All questions can be shared through the online chat function. I will summarize them and emphasize them to Dr. Zimmerer at the end of his presentation. This webinar is live, but it will be recorded. So you can watch it at any convenient time for you. After the recording is finished, you will receive a link with this coming video. For further questions, feel free to use the chat function now or contact us via cmf@brainlab. But now onto our speaker, Dr. Zimmerer.

Thank you, Dr. Zimmerer, for being here with us today. We are very happy that you are talking today about TMJ navigation, I think this is a really interesting topic for all of us. It’s a very difficult topic, and we are looking forward to your experiences that you’re going to share. For those who don’t know Dr. Zimmerer, he is Assistant Professor and Vice Chairman just newly in Leipzig at the Craniomaxillofacial Department. He studied in Freiburg and gained a lot of experience while he was working at the Medical School in Hanover. And we are very happy to have you here today. And I’m looking very much forward for your presentation and I’m looking also forward to the questions. And I have to say, the virtual space is yours.

Dr. Zimmerer: Are you able to see me?

Jana Neider Now we can hear you, thank you.

Dr. Zimmerer: Okay. So this webinar is about total joint replacement and together with [inaudible 00:02:05]. So first of all, I have to give my credits to my old department in Hanover. And I know he doesn’t like it, but Nils Gellrich everybody knows him. He was one of my supporters in my career, and I’m very happy that I could work for him for 11 years. And most of the patients I can show you now, we planned and operated them together in Hanover.

So the replacement of the temporomandibular joint has been a trend within the last couple of years, and several different indications have been proposed so far. From our experience, these are the four main causes for patients needing the replacement of the total joint. So this is ankylosis, first of all. Then rather post-traumatic, then congenital. In Western Europe or in Germany, we have a lot of post-traumatic cases, so with either none or not adequately treated condylar, condylar head, or condylar neck fractures. We also have some congenital causes with aplasia of the mandible with hypoplasia of the joint. So there are different options congenital-wise, and of course post-tumor and defects that have to be reconstructed.

So the topic is about navigation and total joint replacement. So the question is, why you should use or why we can recommend to use navigation in that kind of surgery? Most of these patients or most of the patients that receive any kind of TMJ replacement have some modified or abnormal anatomy, especially in congenital cases. That you can see on the left side, it’s a Goldenhar patient. Then we have tumors of the mandible, we have ankylosis of the mandible. So all these patients share a common abnormal anatomy, which makes it difficult to orientate along the TMJ, particularly if you want to save vital structures like the facial nerve or like the carotid artery or any other structures.

So I will start with this very tricky case we did almost three years ago. And this was a very poor little girl from Syria, and as you can see at the CT scan, she had hypoplasia of the mandible. She had no real joints on both sides. She has been operated in Syria with [inaudible 00:04:34] on both sides. And she was shown to us together with her tracheostomy. So this was her first appearance. And first of all, we more or less relied on our conventional options we have, for example, like, distraction osteogenesis. And the big advantage in that little child was that we had an ankylosis. If you go back to this picture, you can see that she had already ankylosis in her TMJ, and that made distraction very easy. So we could use the skull base with the ankylosis as like an opponent for the distraction, and this one made it really easy and successful as you can see here.

So this was the result only by distraction. But keep in mind that she had no TMJ function at all at this stage, because we used her ankylosis for having successful distraction. So after that, we did what you usually do like in a little child or any patients where you don’t wanna go for an alloplastic TMJ replacement. And you can see that we did a classic post-distraction and gap arthroplasty. We put some fat [SP] graft in it, and she had a pretty good mouth opening for a few months. And then the mouth opening again stopped, she developed again this open bite, and this is like three or four months after gap arthroplasty what we then resulted to have.

So everything we did with distraction and with gap arthroplasty was not strong enough to defend the position of the mandible against the soft tissues. And the soft tissues were so strong that they were more or less retracting the complete result we get. So we did just a simple simulation with the CT scan and we put the mandible in the position where we wanted it to have. And you can see this huge gap between the original mandible and this defense mandible position, and this was where we first thought about using the TMJ replacement.

And also, we had to plan, like, a counterclockwise rotation of the mandible to get her open bite closed. You can see that although she really didn’t have a complete mandible, no joint, no ascending ramus, nothing, all the red areas of bone had to be resected. And this, in a nine-year-old child, maybe you can imagine that virtual planning and navigation might help in such a case to find the correct position and to check, also you have some [inaudible 00:07:13] guides for resection to check where you are during surgery, so for orientation. And that you exactly know where you can resect the bone and where are the vital structures.

So this was the virtual planning of the TMJ on both sides, and you can see that we also didn’t have a lot of bone for screw retention. So we only had five screws per side to fix the plate to the mandible. But you can see, so these are some distances you cannot reach with conventional techniques. I think this is what we can say. So if you compare the position of her lower teeth compared to the postoperative situation after total joint replacement, we gained about 45 millimeters of weight, and this was her immediate mouth opening then after we included the replacement of the total joint.

So this case was just to show you what possibilities are available at the moment with total joint replacement of the TMJ, and maybe just to introduce you to get to know that what kind of support, like instrument navigation might help you in those tricky cases. And this is the very same result after nine months, and now we already have her almost three years after surgery, and she still has a mouth opening for more than three centimeters and the facial nerve is working on both sides.

So this was a very tricky case just to get the topic interesting and started. And why would you use navigation in total joint replacement of the TMJ? So you can support yourself by guidance like drilling. You can do this with navigation by tracking your instruments in the navigation system. You can use your pointer during dissection to know where you are, like for orientation and depth of dissection. And you also can track like a burr or a saw to your navigation system that helps you performing the resection at the TMJ, because most of the guides that are provided by industry products do not include the medial part of the resection towards the skull base where it’s the most difficult part.

And there’s another point why navigation might be helpful. If you take a close look at this planning, you can see that the manufacturer provided us seven millimeter screws for 7.9 millimeters bone behind it. But together with that, they provide us an 11-millimeter stop drill. What means that in a bad situation, if there is some important structure behind this 7.9 millimeter bone, you could hit this with your drill. And those ideas and especially that you need some guidance at the middle skull base and the orientation towards where you have to resect the unnecessary bone, navigation might help you. And in this picture, you can that it’s also possible, although it’s not really necessary, to navigate at the lower part of the mandible at the mandibular angle because usually you can see this very nicely with your extraoral approaches.

You can also see on the other picture that navigation helps you to position your guides and to position your fossa or mandibular components and to find the position of your future screws and where you have to drill. And if you want to drill, as already was mentioned, you can add your drill with the calibration matrix to your system. This is a nice example. It shows you why navigation might be really helpful in tricky TMJ cases. As you can see here with a patient with ankylosis and you can see those two different parts of bone, which might be taken for already the bone, the [inaudible 00:11:20] before the earlobe. But you can see it’s still part of the ankylosis and it’s not already part of the bony ear canal.

So these are some ideas that might show why navigation helps you during orientation and dissection that you know where you are, especially at the middle skull base. On the other side, if you have the STL files of your TMJ prosthesis as in the right picture, you can see how far your dissection has to be taken in order that your implant fits perfectly. And you don’t need a lot of surgical time to try in and try out if the fossa is fitting or not. So navigation can help you during dissection, it helps you orientation wise where you are and where you have to cut bone, and for not mistakenly taking anatomic things that are different than they are in reality.

If you wanna perform navigation with TMJ surgery, I think most of us know that we need a 3D DICOM dataset, usually CT or CBCT scan. It should be a high resolution CT scan with one millimeter slide thickness or less, if possible. We need a virtual preoperative plan, which is pretty obvious. And if provided by the manufacturer, you can try to get the STL data and the implant, and put this together in your navigation system, that makes it possible for you to do the navigation thereof the implant.

But this is, at the moment, a little problem because many manufacturers do not provide you with the STL files, because they are afraid of you using this for…I don’t know whatever strange reasons.

First of all, before you start navigation, I think this has been the topic of different talks before, is how you wanna register the patient to your navigation system. So these are the most common ways of doing this. The easiest way is using landmarks, that means defining landmarks prior to surgery. For example, glabella [SP], for example, part of the teeth. And this can then be used for registration in the OR. A very precise way is using screws. The big disadvantage of this way is that you have to do a small surgery in advance to your procedure to insert the screws. And the patient needs another CT or CBCT scan. There is one option which is quite common because it’s easy to perform and it’s reliable, and it’s just using a dental splint together with four screws, like, any kind of [inaudible 00:14:04] marker you can use. But we recommend you use screws, because you can use, like, the inset of the screw to put your pointer which exactly fits in a a normal 2.0 [inaudible 00:14:15] tool.

Meantime, there are other options for doing registration. And one of these is the skin surface registration and this can be used as well especially maybe in children that don’t need to be scanned twice or three times for CT or CBCT. But you have to take into consideration that during surgery, if you have swelling of the patient and swelling of the face, the registration is not accurate anymore. And keep in mind, if you do a CT scan in a trauma situation and the patient is already swollen, and you do the surgery some days later, it is not swollen anymore. Then you have a big discrepancy between your prior CT scan, which uses the skin surface volume rendering and your actual situation of the [inaudible 00:15:04].

So you can see there are some different options, but the most reliable ones are like the screw, retained the options, for example, dental splint if possible, or the insertion of screws into the skull of the patient.

So if we talk about navigation at the TMJ, we have a small problem. I would call it rather a challenge. We know that we either have to operate but we both have to operate on the skull base and on the mandible at the same time. And the problem is that we wanna have, like, a simultaneous navigation for both parts. Like, lateral skull base [inaudible 00:15:39] and on the other side, the mandible and the condyle. And the problem is that the mandible articulates with the skull base. So now it’s very important to think about this before you do your registration. And very important is the position of your Dynamic Reference Array, which is shown in this picture. If you put it on the skull base or on the head like you usually do for any kind of surgery in the face and the mid-face, you cannot navigate the mandible because the skull reference array is put to the head of the patient.

If you wanna navigate the mandible, you can also put your Dynamic Reference Array to the mandible, but at the same time, you won’t be able to do a proper navigation at skull base and maxilla. There are some ideas which are not very fancy, but they might help you to overcome the problem. But in the end, it’s not solved, it’s just putting the patient into IMF [SP] and using, like, a dental navigation instrument with the same screw markers I showed you before. But the only difference is you can put the patient into IMF. So the splint is for maxilla and lower jaw at the same time.

So a conventional navigation splint, for example, for orbital surgery, which was developed by my former boss, Nils Gellrich and Alexander Schramm from UULM, and it’s like the conventional way of treating mid-face diseases or trauma and the intermaxillary navigational splint is like the possibility to operate on both, and navigate on mandible and the skull base simultaneously.

It means you have to put the patient into IMF. And the disadvantage of the situation is you can imagine that the mandible, at least not during registration, it’s not moveable, but most of the time for just putting…for just doing the condylar resection, you do not necessarily need too much movement of the mandible. But if you cut the wires, then the navigation still works, but the mandible might be in a different position. And it’s always if you put it back into your original position, you exactly know where you are.

Usually, the skull for the skull Dynamic Reference Array is put, and what we did so far, we didn’t put it on the mandible because we thought it would be more important to have navigation at the lateral skull base. And that’s why we put the skull…the Dynamic Reference Array to that. We put the patient into the splint with IMF, and we could use this to navigate both at the same time, like, the skull base where the fossa component has to be inserted or where you have to do your condylar resections or resection of the middle skull base. And you could also use this, for example, for navigating the mandible. But as we know, it’s not so important because the vital structures are most of the time obviously and can be seen easily.

So this is, like, a typical patient. I showed her in quite a lot of seminars because I think she really shows what the problem is with the [inaudible 00:18:51] facial symptomatics. And this is the patient, she had a condylar fracture when she was a child, which was not treated at the time. And her history also revealed that she had orthognathic surgery as well. And you can see in the image that she has a kind of right scoliosis of the face. And you can see this particularly if you look from below. And if you viewed the CT scan, you can see, like, this is almost a [inaudible 00:19:22] facial looking, but it’s post-traumatic and you can see in the CT scan that her joint is not there anymore. And the reason why she came to us was not her looks in the first place, but it was pain in the TMJ, it was arthrosis and resorption of the TMJ, and this is why we started to do planning of her surgery.

You can see in the initial CT scan that she had a LeFort I osteotomy, but we couldn’t find out if she also had a sagittal splint of the mandible as well, and this was 30 years ago. So she didn’t remember, and there were no documentations about that. And you can see, like, the right convex shape and scoliosis of the face and the loss of vertical height in the left mandible and a completely destroyed TMJ in the left side. So another option which I didn’t show you so far because the little girl didn’t have any kind of LeFort I osteotomy, you can also combine total TMJ replacement with other orthognatic procedures like the LeFort I osteotomy and in combination with a contralateral sagittal splint osteotomy. In most of the cases so far we did, the contralateral sagittal splint osteotomy because we considered it like being a balanced osteotomy to give the mandible, like in orthognatic surgery and the two TMJs…so one is reconstructed by the prosthesis and the other is the natural one, to give the chance of more or less balancing into a fixed [inaudible 00:21:01] position.

In those plannings, it’s important that the mandible is corrected first. So, in this kind of surgery, we highly recommend mandible first. So this means put the mandible virtually in the correct position, and plan the TMJ replacement. In surgery, you would also do mandible first and put the mandible in the correct position at the first place. And the second set of the surgery would then be close the bite with LeFort I osteotomy.

This is because the prosthesis has a very nice fit to the mandible, and the result of your whole operation is based on your virtual planning of the prosthesis. In those cases, you can see it’s not a very tricky anatomy, but again, navigation helps you, especially if you start doing these kinds of operations, to know where you are. So to orient yourself along the lateral skull base and the cranial fossa. And you can also see in this picture that we usually try to put a suture through the fossa component and the mandible component to avoid what we call the condylar sagging.

So there is a time in which the scar develops and the healing that takes place, in this situation, it’s sometimes possible, it depends a little bit on how much bone is resected that your fossa and your condyle start distracting from each other. Because simply of gravitation and because the joint itself, it’s a very simple joint. It’s not a locked joint. It’s like a very simple rolling joint which has no real locking component to the fossa component.

But on the other side of this I think is the biggest advantage of that prosthesis that we don’t have, like, a fixed and closed joint. And the movement, which is possible there, this is why this option is a very successful way of doing TMJ reconstruction. You can see here again the virtual planning of the situation, so mandible first. Put the mandible in the right position, a contralateral splint on the other side to make it balanced, one, but also to full orthognatic surgery. You can see the intermediate splint, the [inaudible 00:23:29] splint on one side, and the TMJ replacement on the other side. And finally, you close the bite so that for one osteotomy, you should do a post-operative image, either it is a CT scan or CBCT scan. And you can fuse this with your pre-operative virtual plan, you can see that you have exactly reached where you wanted to have your joint replacement to be.

So this is her comparison between pre-op and post-op immediately. And now she’s over four years with her TMJ, and so far she didn’t have any problems. So one aspect of my talk today is showing you some important design features that should be considered if you want to plan TMJ replacement. So one is the suture hole, which I just mentioned before that widens the condylar setting. Especially if you have long mandible components that are quite heavy, and there’s a lot of dissection being performed because you detach all muscles and all soft tissues from the mandible, you do a segmental osteotomy and then you include a very heavy mandibular component. And then it might get distracted or loosen out of the fossa.

So you have two options where you put the suture hole. You have the anterior suture hole, and it’s pretty obvious that if you use this kind of suture hole that you will have a restricted mouth opening. That means you have to open, after surgery, the mouth completely. And if the mouth is open completely, then tie your suture. And this is what the maximum mouth opening is possible. And if the mouth is closed, you can see that the suture is not pinched. So if you wanna have the more stable condylar position especially doing mouth openings where you don’t wanna have condylar setting or you don’t have…or you have a big prosthesis which is more likely to get dislocated out of the fossa, we recommend to use the anterior suture.

On the other side, you can also choose a posterior suture which gives you more movement of the mandible. It’s a less restriction of your mouth opening, but it’s again less stable in your condylar position, so you can choose depending on the underlying cause, what kind of suture hole or if you don’t wanna use it at all. But so far, we have done this in every TMJ reconstruction so far, and I can say that we didn’t have any condylar setting so far.

This is just an image showing you with the different options. So one patient was just a normal TMJ reconstruction, and the other one was an ankylosis case. So with the ankylosis one, I have less restriction. That’s why we put in the posterior suture hole. And the other one was, like, a good mouth opening, almost [inaudible 00:26:27] mouth opening. And there, we didn’t want to have condylar setting at all. And that’s why we used the anterior suture hole. And this is how it looks like during surgery. It’s very important to put the suture through the components before you finally screw and enter them, because otherwise, you won’t be able to put the sutures through the small holes.

If you talk about it like, it’s the time of 3D planning and virtual planning, and as you can see, these are all, like, patient-specific implants. And you don’t have any kind of limitations. The only limitations you have is, like, whether the implant is made by a drilling procedure or if it’s [inaudible 00:27:13] manufactured with printing. This is high difference in precision. But no matter what technique is used, you can, for example what we did in this case, include those flanges. And those flanges help you to position your condylar prosthesis more precisely according to your virtual planning in addition to your cutting or drilling guide, because sometimes the drilling guide or cutting guide cannot be fixed precisely to the mandible because sometimes it’s too extended. So those kinds of flanges help you find, like, a one fit only position of the implant according to your planning.

You don’t have any limitations in including bone grafts to your planning, and you also can use those modern techniques to camouflage mandibular defects, which might be visible from outside and which cannot be reconstructed with other options. So you can also try to implement this in your design of your virtual prosthesis.

There’s another option if you don’t like the flanges. If you wanna have your implant completely wrapped around the ascending ramus, you can choose this kind of design. And this also helps you to find a better position, especially if you include a bone graft. Like, in this case, it’s a two-segment fibula for a mandibular reconstruction.

So you just have to talk to the designer on the other side of your computer and tell him exactly what you want. And there are many design options, and try to find the best for you, and try to use modern techniques that help you to really identify your final operating position [inaudible 00:28:56] and that you don’t have too many options of positioning your implant.

How can we take control what I said in the very beginning about drilling during surgeries, navigation, about dissection during navigation and resection? Drilling is, like, the very last instrument that is provided with the Brainlab. Brainlab system is the calibration matrix. And the calibration metrics allows you to register any kind of drill and burr according to its diameter. You can see this on the right side of the picture, [inaudible 00:29:31] with different diameters for your drill. And you have to mount another reference array to your drill, and then you can in real time navigate with your drill of choice or your burr of choice, and see in real time where you are in the patient’s anatomy.

This is just a small excursion to explain what is trajectory based navigation. You can define in the planning software provided by iPlan, a target. This means a target, where do you want to go during surgery or where do you want to have the screw placed or where do you wanna have a dissection stopped? This target can be defined virtually. And on the other side of the target, you see or you define where you have your entry. For example, this is the way how you wanna drill from an entry point to the target and in between, the computer generates a line. And this is a trajectory line. And with the trajectory navigation, you can follow this line with the autopilot function. And this gives you the option to follow from the beginning of the entry of your surgery.

For example, if you wanna drill a screw hole, and you know the end where you want to have the tip of your screw to be, then you can use this kind of very simple and helpful tool. And this is included usually in most of the software. This is an example like drilling the fossa with the skull base. And you can see this is a popup window that shows up if you do the registration. You can see we used the 2.5 diameter drill and it was a very precise registration. You can see the middle picture. This is the autopilot function. And the three views, like the coronary, the actual, and the sagittal view that in three dimensions, you can see how you drill.

And this is the video of real time drilling following this blue trajectory line, and in the left side, in the left upper quadrant, you can see your autopilot which also shows you that you have to stop, target is reached. And you have reached the end of your trajectory line. And take a look at this picture. This is a drilling procedure close to the…or it’s at the [inaudible 00:31:52] skull base. And this helps you to identify how far into the bone you wanna drill, and if you…and that you can preserve vital structures and don’t hit them during the surgery.

The resection’s pretty much the same. You don’t need to use this pre-drill [inaudible 00:32:13] calibration matrix. You can also use the other options. For example, if you wanna have [inaudible 00:32:18] instrument or a saw, or like in this case it’s a burr used during resection. And you can see that it’s a very precise deviation of the tip according to the virtual planning. And especially in those cases where the guides that you are provided by, they do not include the ball of resection towards the middle skull base. It’s just either like you take a ruler and measure how far you can go, or you can also use a drill or burr that helps you during resection, and that helps you either way not to harm any vital and important structures.

So this dimension is usually not included in the guides provided so far. On the other side, if you would design the guides that would include that kind of distance towards [inaudible 00:33:08] skull base, you know how [inaudible 00:33:10] and big it would be, and it’s almost impossible to include this in a normal [inaudible 00:33:14] approach.

This is a patient I want to show you. She had a condylar fracture of the neck, under the neck, which was treated operatively, but she developed pseudarthrosis. She had three or four revision surgeries and she had this occlusive disturbance. And so we included a total joint replacement on the right side, and then just for balance, a sagittal splint on the left side. And this is a picture from the OR in Hanover, and you could see that we could use the intraoperative imaging, and you can also see on the picture in the back, there’s the Brainlab Curve System. And it’s if you intraoperatively acquire a 3D dataset, it’s the high resolution one from the C-Arm, you can do an intraoperative fusion of your virtual plan and your outcome. And during, the patient is still under anesthesia, you can check whether you have reached your goal or not.

And this is just to show you, because we did the sagittal splint on the other side, this is the position of the condylar on the side where we did the sagittal splint. And you can also check whether you have a dislocation of the proximal segment during your sagittal splint, osteotomy, and fixation. So intraoperative navigation can be nicely combined with [inaudible 00:34:39] imaging, and combined with your preoperative virtual plan. When you cannot only check what you have included in terms of implants and screws, you can also check like the post-operative position of your mandible.

What we have reached so far is that we could operate like in the last two or three years, 26 patients with TMJ replacement, and most of them had a limited mouth opening. And you can see that we gained with the TMJ replacement, a statistically significant improvement in the maximal interincisal opening, compared pre-op to post-op. And most of the prostheses had between 35 and 40 millimeters of mouth opening, compared to 20 to 25.

On the other side, the most important things that we can give to our patients is that we can improve mouth opening. And most of the patients have at least a reduction in pain, and this is also statistically significant. This will be published soon, hopefully. And you can see, so in those two clinical TMJ related parameters, the TMJ replacement helps. However, it is very important to do the right diagnosis. So if you have a patient just with splinting or with unspecific pain in the TMJ, or especially, like, patients with muscular problems, they will not benefit from TMJ replacement. They will rather not benefit from it. So it’s the opposite.

Patient connection is the most important thing you have to consider during this planning and this reconstruction of the TMJ. And if you do the correct indication, patients usually do profit.

If you see…if you take a look again at the intraoperative imaging, which is fused with my pre-operative virtual plan, you can see this window. In the window is post-op and out of the window is pre-op. You can see that you can also include the trajectory lines and you can see behind them, the screws and you can see that there’s still a deviation to your plan’s horizontal trajectory line. Because we don’t have proper cutting guides or drilling guides at the skull base that really guide you, so that’s why we developed this navigational approach because the industry partners so far will not provide us with guides that include the lengths and the diameter and the vector of the screws.

We did an analysis of patients we just operated with the trajectory planning, what I showed you by just tracking the drill and doing the screw insertion. And we did it without a trajectory plan. And we could see that we had a high deviation between the different screws, so S1 to S5, from 26 patients, all the screws starting from screw one to screw five. And we also could show that there was no real statistical difference between using a tract [SP] drill and not using it. But again, the precision is a little bit better, and it also depends a little bit on your learning curve and how experienced you are by using this drill.

On the other side, this is like checking if the condylar position in the virtual plan is the same in your outcome. You can see in this image fusion that although we were using navigation, although that we were using cutting guides and drilling guides for the mandible component, that still you have…it’s a small deviation, but you can see in this image that still we were not able in most of the cases, to reach the perfect outcome. And this is what you can see here that we still have a condylar deviation between the transverse, vertical, and sagittal positions. So this image is just important to show you that there is still a way of improvement possible for better positioning your devices according to your planning. So still, we have not reached the perfect result of transforming our virtual plan into the patient.

This is one of the last patients I did together with my boss, Nils Gellrich in Hanover. It’s a patient of his. And she has the Goldenhar syndrome, and like many of those patients, she already had some surgeries prior to TMJ replacement. She had distraction, which is usually done by those patients. And you can see, again, that although she has nice occlusion, which I will show you later, that a lot of results gained originally by distraction relapsed. The occlusion is fine. The patient has nice occlusion [inaudible 00:39:46] speaking, but still from the outside, you can see there’s heavy facial symptomatic, which does not usually disappear by distraction. Or on the other side, it’s not really stable over the years during growth and during, like, resorption of the distracted bone and relapse.

You can see, like, the occlusion itself, anatomically speaking, it’s good. But you can see the occlusive [inaudible 00:40:12] and again, these heavy facial symptomatic, in this case, congenital. So not post-traumatic like the other case I showed you, but congenital. And basically it’s the same problem we have to treat. So this is the occlusive [inaudible 00:40:29]. You can see the virtual planning on the healthy side, and you can see that she didn’t have a TMJ at all. She had like a very strange and abnormal anatomy. You don’t know exactly where the facial nerve comes out of the [inaudible 00:40:46]. You don’t know where the big vessels are. So everything is a little bit different in her, especially at the skull base and the facial nerve. And this is, like, the virtual planning. We did the mandible first, and then the LeFort I to close the bite.

So we put the mandible first in the correct position. We resected most of the bone that had been distracted prior. And we also then included the LeFort I to close the bite. And did contralateral sagittal splint on the other side. So in those cases, the TMJ replacement can be considered rather a line extension to orthognatic surgery than anything else. And in those cases, sometimes we have a too small mandible, you can always use the virtual planning and different design to give a camouflage of the patient that you more or less balance those deformities with [inaudible 00:41:39] material.

This is looking from behind. This is like a modified big facelift approach. And the only structure that was not dissected in that case is really so the facial flap of the skin of the face was only [inaudible 00:41:56] to the facial nerve. And in those tricky cases, you cannot mount your TMJ components directly to the skull. You have to use, like, a titanium basis plate. And on top of the titanium basis plate, you can then screw it in your fossa component made of polyethylene. So this was the contralateral sagittal splint, the TMJ replacement on the side. You have the intermediate splint, and in the end, you do LeFort I to close the bite.

This is her post-operatively. She didn’t have any condylar setting, so don’t take this mistakenly. Because the polyethylene is not really [inaudible 00:42:36] and you can’t see it in the x-ray. So if you compare this pre- and post-operatively, you can see that we almost reached a horizontal occlusive plane, but still not perfect. And again, maybe we can for the future do even more than this instance in those kind of surgeries. Because with the TMJ, you have almost unlimited possibilities in distance and ways and deviations of the mandible you can achieve.

So finally before I come to my conclusion, it’s very important, again, if you want to have a successful treatment for your patient to do correct selection. So the total joint replacement is really for patients that have, like, multiply operated TMJs that have post-traumatic diseases that have other end-stage TMJ pathologies or congenital deformities. But don’t treat patients with normal clicking, and unspecific pain and morphologically normal TMJs [inaudible 00:43:42] replacement. And if we’ll take this into consideration with navigation, we could show and we will show that the publication which will be available soon, that it’s feasible to use navigation in TMJ replacement. It helps you that can navigate simultaneously mandible and skull base.

The registration method with the intermaxillary navigational splint does work. However, the mandible is at least during your registration, it’s fixed. We have a high accuracy which is more…which is less than one millimeter, compared to other surgery. We can use the instrument tracking device, the calibration matrix for mount our instruments into our virtual planning. And we can use intraoperative… So this is German, I’m sorry for that. The intraoperative quality control by fusing intraoperatively our virtual plan, and the outcome during the patient is in general anesthesia.

So these are my final conclusions. I know I was a little bit late and a little bit too long. And I thank you very much for your kind attention. And if you are interested in any kind of those procedures, just email me or if you wanna have any kind of slides or pictures, please just email me, and don’t use any screenshots and I’m sure I can help you. And thank you very much for your attention. And now, I think we can do the question and answer session. Thank you very much.

Jana Neider Thank you, Dr. Zimmerer, for these wonderful and amazing clinical pictures. It was just amazing to see what clinical outcome you reached with navigation and all the planning that you have performed. And I have to say already a few greetings that we received. So I just had a call with Professor Esik [SP] a minute ago, and he sends you very well greetings. From [inaudible 00:45:30] we also received greetings from Columbia for you. I think even some more greetings for you, but maybe we start first with the questions.

And here, I would like to remind all the participants that they can still send questions through the chat function. But as we’ve already received them, I think we will start with the first question. And the first question is, how much time do you save with navigation? Or is it not so much about the time saving, and rather more about the clinical outcome that you can reach with navigation?

Dr. Zimmerer: So to be honest, you don’t save time doing surgery and you don’t save time pre-operatively. Because you will need to spend time during planning, and you will need to spend time in just setting up all the instruments during surgery. So at the beginning, it’s a little bit tricky because navigation, like, it has a very flat learning curve, and you need to learn to be able to interpret what you see on your screen. So to be honest, at the beginning, it takes time. It takes more time and it doesn’t save time. But in the end, on the other side, just being so into your case, doing all the planning, and do your analysis, and you see where you wanna drill, and you see how long you wanna drill, you have a much better understanding during surgery, in every dimension, that it really is helpful. Yet, at the beginning, it doesn’t save time but it helps you transforming the plan you have generated into the patient at the end, I think more precisely. But it needs training, yeah. It needs training.

Jana Neider Thank you. I think that is valuable feedback. Of course training is always needed for such cases. But I think it supports also the difficult cases and really helps you with the learning curve. One other question that we received I think multiple times is, if you can explain more in detail how the patient registration works with the splint that you are using? Are you loading this as an STL? That was another question. So how does the splint work with the patient registration?

Dr. Zimmerer: So the splint works very easily. You have to do a second scan. So whenever you have a [inaudible 00:47:51] that you wanna include into your planning for registration, you need to scan the patient. So this is what we did in those cases. So the navigation splint or the intermaxillary navigation splint is mounted to the patient. He’s put into IMF, and then we do a complete CT scan for registration or we do the planning CT scan for the total joint replacement. For that kind of registration method, you need a second image.

However, there are different options where you don’t need another image for registration. But this has like everything else, advantages and disadvantages. The small disadvantage of this method is that you need a second scan. But again, your way of operating and your patient safety requirements are better by using this, and that just using another CT or CBCT you can have more precise planning, and intraoperatively a better orientation where you are.

There are some studies, and I think Alexander Till [SP] from Hanover, he did this. You can also do an STL file based splint and include it in your planning as well. So this option does exist, and it works, but it’s a little bit more…it’s not a little bit more, it’s more complicated. It’s a little bit more time that you have to spend, but it is possible to use a virtual splint as an STL file included into your planning, and you can use this as well for registration.

But what we could see so far, we also tried like the skin surface registration, and like big surgeries for TMJ replacement, we do not recommend this because you cannot go back and do the registration again once the patient is swollen and you might have any deviation during navigation. So do any kind of fixed, the best is screw retained markers for navigation, or you can also use the virtual splint method if you are able to do this.

Jana Neider Thanks, Doctor, I think that…

Dr. Zimmerer: Yeah, you need to rely on the system, and the one thing that happens if you are, like, after five hours of operating, you can see that your precision is not good anymore from navigation system. And then you have to do a registration again, and for this problem, you need something which is reliable. And the screws are reliable either on a splint or drilled into the patient’s skull prior to surgery.

Jana Neider Thank you. I think this is really interesting information to all the people that are using navigation and not had yet this extensive experience. So I think we could do even a whole webinar just from patient registration. Maybe that’s something we’re gonna do soon, because we see there’s a lot of questions on that coming in, so maybe we can schedule something for that as well. And I think you answered another question. The question was, can you record STL into the navigation system? You answered that in regards to the splint. But I think of course this is also possible for all kinds of implants. So if you have an STL file, you can import it into the navigation. And I think you are doing that quite often.

Dr. Zimmerer: Exactly. And I mentioned at the very beginning of my presentation that it depends a little bit on the manufacturer. So we have big problem of receiving the STL files of the TMJ implants from Zimmer Biomet, which are situated in the United States. And for them, it’s they are afraid of us doing any kind of stupid things with the STL files. But at the end, we would not even need the STL files, we only would need like a trajectory line like I showed you in the planning, that we can include this in all navigation systems. We would not even need the shape of the condylar and we would not even need the shape of the fossa. We only need the position of the screws and the vector and the lengths and the diameter. And this is the only thing we’d use, but it’s still very complicated to get this from huge companies in the United States. It’s much more easier if you have other companies, they are very easy and helpful in providing those STL files.

And there’s another thing you have to take into consideration, and I think this can be answered maybe more precisely by the Brainlab technicians than by me. You have, like, a kind of system… Now, I’m just trying to find the best words to explain this. It’s like a coordinate system of the STL file. This is sometimes different to the coordinate system of your planning in Brainlab [inaudible 00:52:55]. And if you then include the STL file of a company which hasn’t worked with Brainlab before, they don’t know each other’s coordinate systems. And then you will have an STL file pairing which is completely out of the way, completely disoriented, or mirrored like 90 degrees around. So it doesn’t fit.

This is a problem for you to take into consideration. If the company is not working with Brainlab, you might have those problems not getting those STL files orientated to the skull. But if you send the skull of the patient yourself in an STL file, they can match it to this and send it back to you. So you have some options, but it’s a little bit complicated. You have to just keep this in mind, that there are different coordinate systems for the different STL implants.

Jana Neider Yeah. I think we have good news for all our customers who will come with the new software, this coordinate system will be solved so then you won’t have this issue anymore. And this is something coming very soon to the market, so we will inform you as soon as this is available. But I think this will definitely support this little customer issue that we had here for a while with the [inaudible 00:54:10] coordinates. So this will be way more convenient for all of us.

There’s another question coming in and the question is, what is the incident of PJI using navigation versus no navigation?

Dr. Zimmerer: What is meant by PJI?

Jana Neider I think the question was more in regards to how do you use navigation, for which cases would you use it, and for which cases you wouldn’t use navigation? Also for TMJ, would you always recommend to use navigation for all surgeries? Or is it just for specific cases where you would recommend to use navigation?

Dr. Zimmerer: So when we started doing TMJ replacement, we used it for any TMJ replacement surgery. And again, it’s something about learning and learning curve. And if you don’t do this on a regular basis starting from planning, registration, your OR personnel has to be taught how to use, and the residents in the OR. So everybody needs to know how it works. Otherwise, it’s not helpful in the OR. It might be a real mess. So if you wanna make this, like, a standard thing, I can recommend to start using it for any kind of TMJ replacement.

And then you can see how it works, you can learn what your screen is really showing you, you can put the anatomy you see maybe in an easy way, in an easy case where it’s just a [inaudible 00:55:46] and everything else is fine and you know how far you can dissect, and then you learn, and that, later, it’s helpful for the complicated anatomies. It’s very hard to use navigation in those complex cases if you are not able to use it in the easy case. Because an easy case, you know probably the anatomy, which is not completely abnormal. But in the complex cases, you really need to be able to work with the navigation system and be able to interpret what you see.

So if you start using it, I would recommend using it as often as possible, like, everything you learn and train. And if you’re used to it and your OR personnel is used to it and the residents know, like, it’s a standard procedure, navigation, splint, registration, implant, import, then you can maybe use it only for the complex cases. So one is for training, the other is then to be able to use it in the complex cases where you really need it. But yeah, I would do this for everything with navigation, even a simple zygomatic fractures you can train. And if you know how the easier things go, you are really happy if you need navigation in the complex cases, with every technique.

Jana Neider Thank you. There’s another question. So we also received for the PJI, PJI is prosthetic joint infection. But I think the answer if you should use navigation or not, stays the same. So you should always use the navigation system for training yourself to be then prepared for the more difficult cases. I think that also goes for prosthetic joint infections. The next question is, which material do you use at the suture of the components of the TMJ replacement?

Dr. Zimmerer: So as you could see in the pictures I showed you where the prosthesis were provided by a Zimmer Biomet from United States. And the fossa component is polyethylene. And this is the kind of material which is highly recommended for any kind of TMJ replacement. So, so far, I would not try using anything else, any kind of materials that has not been proven in the human body. And polyethylene has been used I think for 50 or 60 years like in orthopedic surgery. So this is a safe and very good biologically adequate material. And on the other side, it’s titanium. If you want titanium for the mandibular component, or the other option is steel. You have to take into consideration that the steel option, there’s nickel. Nickel, what’s the English word for nickel? So we have to be aware of patients having any allergies to this kind of metal, which is I think 10% of the population usually have any kind of allergy to this kind of metal. So most of the time, we use titanium, because we don’t wanna risk an unknown allergic reaction to cobalt-chrome steel, yeah.

Jana Neider Yeah. I think totally agree. And nickel is actually the same in English, so I think that’s international speaking. And yeah, we see a lot of patients that are allergic to that, and so the recommendation is really good.

Dr. Zimmerer: And this problem, if you use the cobalt-chrome steel prosthesis and we have problems with patients who has discomfort, maybe has swelling, maybe has pain. You don’t know exactly if you have a rear joint infection, or if you have an allergic reaction to cobalt-chrome. Because depending on the population, it’s quite a common allergy. The easiest and safest way is to use titanium, because otherwise, you always might have in the back of your mind, “Now is this an allergic reaction? Do I have a rear joint infection? Do I have anything else which I cannot explain?”

And this factor of uncertainty you can completely reduce so far by using titanium. Or if you have a negative nickel allergy test. But, okay, this depends on you if you wanna do this on a regular basis, all the time.

Jana Neider Thank you. The next question is, do you have any recommendation or tips for calibration of the navigation system, especially in bilateral cases? So the biggest issue the customer has is that if you have a calibration really good on one side but not so good on the other side, but you have the defect, are there any tips and tricks that you could share with the community?

Dr. Zimmerer: For registration, the most important thing is that your registration markers have an adequate distribution around the defect or the zone where you wanna operate. So I don’t know how you get the registration in that case. So you have to be aware that your registration markers should be in a different place in the virtual space. And the best is if your defect is more or less in between those registration markers. You want your registration marker close to that. So maybe you should change the position of the registration markers you use. And the other option is that maybe your skull reference array, which usually I think most of us put it on one side, because you cannot put it in the middle. But to put it more to the center of the head, of the skull, might also help. So you have to choose your registration points carefully. You should not use usually more than four, because otherwise, it can get more emphasized the more markers you use, so four are usually recommended. Then you should put them in different planes and levels and not every marker should be on the same level. Then I think you have the highest security in registration.

Jana Neider Yeah. Thanks a lot. I totally agree. I think it really depends also on the angle, how you put the screws, for example. I think this is really important to also improve the registration result. That was the last question that we received, but we still have received some nice greetings from Hanover, from [inaudible 01:02:24]. So Professor Gandy [SP] says hello to you, wishes you all the best in Leipzig. And I have to say thank you for that wonderful presentation. It was amazing. I think it’s very impactful. It’s a very interesting topic. We received a lot of questions. Also we received questions, if we can share your email address, because there is still a lot of attendees that have some special questions for some difficult cases. So is it okay for you if we share your email address afterwards?

Dr. Zimmerer: Yes, I think it’s still on my final slide. I don’t know which slide at the moment it’s on. But yes, you can share my email address. And if you show my screen again on my final slide, it’s on there.

Jana Neider We can [crosstalk 01:03:11] to the participants. Thank you. So then, I thank you a lot for that wonderful topic. We have the next coming topic on 24th of November with Professor Frank Wilde from the University Hospital at Ulm. He will talk about secondary orbital reconstruction [inaudible 01:03:27] deformities. I think that’s also a very special topic, very interesting. And we are looking forward to that. Dr. Zimmerer, thank you again for that presentation. For everyone that still has questions or wants to follow us for more webinars and more insights on Brainlab, please send us an email to [email protected] or follow us on our social media channels.

Thank you, Dr. Zimmerer. It was a pleasure to see you again, and thank you, all the community out there, for being here with us today. Thanks a lot and goodbye.

Dr. Zimmerer: Thank you for the invitation, and greetings back to my old hospital, to Hanover, and to [inaudible 01:04:05]. Thank you very much and hope to see you soon.

Jana Neider Thank you, Dr. Zimmerer, have a good day. Thank you, audience. It was a pleasure to see you all.