Pediatric orthopedic surgeon Mohammad Diab, MD, one of the innovators behind the tethering procedure, explains this safe, increasingly popular surgical option for severe scoliosis. Delineating the caveats as well as proven advantages, he describes how tethering can allow children to move more normally and what’s currently known about timing the treatment with a patient’s physical development.
mm hmm. Hello. My name is Mohamed Diab. I'm a professor in the department of orthopedic surgery at UCSF. And I'm a pediatric orthopedic surgeon. And beyond that I'm specialized in that. I spend most of my time in the spine and the pelvis. I'm going to talk to you today about spine tethering in the broadest sense meaning the ways in which we have and continue to tether or bind or modulate the growth of the spine in patients who have scoliosis. I always start with this slide because we had to um show this when the FDA came around. The FDA sent letters years ago too. I think four centers and one of them of course was ours because we were doing this and cautioned us. Now we can at least say that this is FDA approved and this is becoming old news but still it's worth reminding everyone that it is um so that people can have confidence that this procedure does have benefits and is safe. It's not new. I put two studies there, one from the 1950s which is an experimental study um in dogs. And then one clinical study just a few years later and you see there that a staple is being put in the front of the spine and that's sort of the original clinical application of spine tethering. It's not even then it's not an original procedure because that's staple that's being used. There is a staple that a surgeon called Blount invented a decade earlier for the knee. And we have now a half a century of experience with growth modulation around the knee taking crooked knees and putting in staples. Now we put in something else more modern. But the concept is we know how to make crooked bones grow straight outside the spine. And so it made sense back in the 50s to try it in the spine. And it makes sense now to retry it in the spine. Um this is what got me going back in the 2000s. A paper came out from France from a group whom we all know and can believe. And it said that For patients who are under 10 years of age we call that early onset scoliosis Who have a curve greater than 30° bracing doesn't work. And in their series all the patients went on to spy infusion. So that got us all thinking or got a few of us thinking that that's a group of patients that we are not addressing well because the current treatment at the time was bracing and those patients were escaping that treatment and ending up in a fusion. So back came the staple again from the fifties actually forties by a man called Brown. Then the fifties applied to the spine and now reinvented because the metal changed and it was a night in all metal which is memory metal you put it in straight and then it curved so it held on and didn't dislodge. That was the problem with the original version of stapling of the spine to tether it. And it worked well. We wrote this paper as the first biomechanical biomechanical assessment of thoracic spine stapling. We use the thoracic spine because it was the most common. And we showed that biomechanically the staples held on and they were they were effective in that they allowed motion. And this is what we could do. We could take an almost 40° curve in a young patient under 10 early onset and we could tether the convex side which is growing faster and not touch the concave side which theoretically is growing slower but still growing. And with further growth the spine would spontaneously straighten. And in 2013 we published our results, you know bets and I published our results um and we identified the right patient, two undergo tethering at that time with a staple. Then came a paper a single case from ST louis where they tried a different implant they took, they re applied an old implant that was designed for older patients in the back of the spine low lumbar, that means low lowest part of the spine for back pain because of spinal stenosis. So you can see no none of those components applies to a child with scoliosis. It's a child or an adult it's scoliosis not spinal stenosis, it's more often in the thoracic spine but also in lumbar spine but not just exclusively lower part of the lumbar spine but still um that implant system was adapted, thinking that the staple might not be as strong for a bigger curve. So this is their example Of a patient who was eight and 6 months old. In this case a boy with a 40° curve. And this is what happens with growth again. Go on the convex side tether that so hold it while you allow concave growth and then the patient can spontaneously straighten and there is no fusion there. This is what it looks like. Um It's a screw that is made of titanium that's coated by something called hydroxy appetite. That coating incorporates or interdigital dates with bone and makes the purchase or the security of this crew better. And then you connect the screws with a dacron cable. Nothing fancy. It's just one form of polyester. This is the original paper where it was applied to the low back in adults and this is what we can do. We can take now an older boy with a bigger curve. This is one of my early patients who had been braced for about five years from 6 to 11. Now it comes to me at 11 with increasingly an increasing curve and we put it in the tether and he grows straight. Um This is how we do it. I do it open. I'm the only person who does it open. Everybody else doesn't buy a telescope. But my rationale is You can have multiple 1-2 in incisions or you can have one single incision and what I try to do is go between muscles do it open. I feel like I can control it better. For example we've never had a transfusion and we've done many of these but there is a certain transfusion rate because sometimes it's difficult to control the bleeding with the telescope When you do it open you just have a little bit more control. Um I do it by going between ribs and you can see the implants there and obviously all that language on that slide is just reminding us that it's high priced real estate and you've got to be careful. The problem with tethering is there are many, many questions that we still, I have not answered the first. The most obvious one is what are the indications when we do surgery? There is a judgment on who should undergo an operation. Um This is what I think now, but there is no absolute consensus. Every surgeon who does this has maybe a different approach but the key is we want patients to be young enough but not only do they benefit from the motion conservation. They also benefit from the growth modulation. I can put it together in a mature patient and it will conserve motion more than a fusion but I would not expect a mature patient to grow straighter um and thereby get completely straight and also relax the cable so it's less prone to fracture. So the ideal patient has enough growth remaining that they will grow after. They are tethered. The tether will affect a partial correction. Um and then the growth will complete the correction and thereby relax the cable. And if the cable is relaxed it will be less prone to fracture. The next question is, how much do we tension it? It is this is um a photograph or a diagram of the original system and now there's a new system but it's essentially the same sort of concept. We don't really know. This is what I do know if a patient has is very sort of immature. I'm just gonna lay the cable in because I don't want to overdo it because then they'll grow a lot and then they will overcorrect. If the patient is mature, then I get as much tension ng as I can safely to correct the patient as much as possible. And in the words of john hall who's there, who's one of the people I trained with, you sort of the the the towering figure and pediatric spine surgery. Um He's passed away now. Um you tension it just enough and not too much and that's where surgeon experience and certain judgment matters. It's not simply a technical exercise. There's a lot of finesse in how to sort of play around with the system and when to implement the system um that I hope patients sort of pay attention to how much motion is preserved. We say that it's better than fusion. And that is true. I always help our trainees that the bones of the spine are called vertebrae and that the vertebra, the word vertebra, that's the only bone in the body that is named after its motion. So to do a fusion is crazy. I mean we do it because often because there's no alternative or the alternative is worse. But if we can we do want to avoid fusions because the movement in the spine is essential. The issue is we still don't know how much because we know that we put a cable in there and that cable is under tension. So it's not normal. Okay. It's certainly better than a fusion Where the movement is zero. But it's not like we create a normal spying. It's another reason why we want to try to get the kids when they're young, when they have growth remaining. Because the more they can grow, the more they will relax the cable when we put the cable and intention, it's under tension on the convex side as the concave side grows, then the cable will get less and less tense. And so the movement of the spine will be improved. And I think the best thing we can say is that movement is preserved in all planes except the way in which the scoliosis is bending and the sum is I'd be happy if the patient Had about 50% of their normal motion. Maybe more. I think 50% is the floor, Probably more than that. This was the most pessimistic estimate. And that's why I think conservation is a better word than preservation. We don't preserve motion in the sense that it's 100%. But I think we conserve enough of it that the spine will be healthier and the child will function better. The durability of the implant is in question. All right. There's no doubt about that. The implant can be divided into two the screws and the cable, the screws are fine. They don't break the screws don't pull out of bow. And I've seen I have seen a few examples that come to me, but they're very rare and none of our patients has had a screw failure. So the screw is fine, but the cable is the fragile part of the system and the cable can break. Um And this is what it looks like. You can see the white arrows there show um cable broken in between screws. We don't really know why it happens in one patient versus another. It's not clearly activity based because I have patients who play football who are very active and the cable is held up. And then I have patients who aren't particularly sporty. And the cable has broken. The one thing to know is that the patient is not injured if the cable breaks, they don't even feel it. What we'll notice is during follow up. We'll get an X ray and we'll see that the screws at one level let's say start to diverge or grow apart as though the cable isn't holding them anymore. And if that happens then we can decide what to do a lot of times. We don't have to do anything. But if that happens and the patient gets more scoliosis again then we can decide what to do based on that. What is the fate of the inter vertebral disc? So we're now talking about bone, we put screws in bone and we connect them with a cable but there's a disk in the middle and that disc is the squishy thing. That is one of the centers of movement of the spine. And that's how you know when people get older they get disc disease, degenerative disc disease because the disks wear out. But when you bind them up, even though you're only buying them up partially. Is there a problem for disk health? It's a it's a natural tissue that needs normal movement and now the movement is abnormal. Um And so we still don't know. However, at least the early results suggest that as long as you don't mess with the disks, you stay away from them, you put the screws in the bone and the cable traverses the discs between the bones that they're probably going to be okay. They are deformed. The tissue is deformed but it doesn't seem to wear out any more quickly so far and it's not a source of pain. My tether patients are pretty asymptomatic. So I think that the disks will hold up at least for the current duration of follow up that we have, which is about a decade plus in reasonable numbers. What about the growth plate? So what happens is we put screws in the bone and they across the cable crosses to the next bone and so on. But every one of those bones has a growth center, not just the diskettes in between, but also growth center. And we don't know if some patients will have what's called a growth arrest and their spine will stop growing entirely okay. And so it becomes a permanent growth arrest. And we have this experience with the vertebral staples in some patients, they caused a permanent growth arrest. That is relevant because if we do this in a young patient who has, let's say, a big scoliosis and and the two young to fuse, we also don't want to create a growth arrest because that's mimicking a fusion for the length of the spine. It's not making a fusion for the motion. They'll have the movement but their spy might end up growing short. It doesn't seem to be the case right now, but it's definitely something that we're sort of paying attention to. What about what happens when patients overcorrect. If we are too eager. Either we intervene too soon or in an immature patient, we tension the cable too much to get too much of a correction. We might then end up with an over correction if the child has a lot of growth remaining. And I'm often having this conversation with patients. I tell them, look, I can make the spine pretty straight because your child is young and by nature of being young, flexible. But if I get too excited, too carried away or I want to impress you too much by creating this, you know, beautifully straightened spine. Your child still is going to grow on the other side. And what's going to happen then is what was the concave itty? The shorter part that wasn't growing as fast as it grows, it will now grow too long and become the convexity and start to overcorrect and give you the opposite curve. So this is an example of a patient I did who started to overcorrect. She had a curve That pointed to the right, it was about 50° but she was young. Um, and we put it in and we did pretty well, but once she started to slightly over correct, I went back in and I slackened the cable so I put these kinks in the cable so she could bounce back into a little bit of scoliosis. And then she grew some more and that's where she ended up and I think that's a good result because her motion is conserved. And you know, she started with a 50 plus degree curve. And so that's pretty good considering those sort of criteria. And this is one of my earlier patients and she's now she's almost gonna graduate from USC and she's doing pretty well and she's never I mean she's been very happy and she's functioning essentially normally. There are hybrid techniques that the public should be aware of and other surgeons are going to do this. This is an example of a patient who came to me with these big curves and I felt like the thoracic curve was just too big to tether and the lumbar curve is big too. However the benefits of motion conservation in the lumbar curve are so great that it's worth trying whatever you can do. And so this is an example where we did a fusion in the thoracic spine because saving motion there isn't as critical. And then we did a tether in the lumbar spine and again it's one of my earlier patients and it's holding up quite well. What about the approach in surgery we talked about approaches in the spine. You can go from the front which to the public looks like it's going from the side going through the chest to the spine or you can go from the back. So anterior front, posterior back. And this is an example of a patient who has a lot of growth remaining and two big curves. Most surgeons would fuse these but instead what we did was we decided to tether the spine. We went in the front in the chest and we went in the back for the lumbar curve. I was the first person to do this. And I remember years ago I think of 2016 I gave a talk at the American Academy of Orthopedic surgeons and I you know give my experience with going from the back in the lumbar spine. There's a technical aspect to this which is that if you go in the back you restore the patient's sway back. That's a normal thing. If you go in the front you tend to reduce sway back and that can be a problem long term for patients. You create what's called a flat back. Um and so going in the back has that advantage. I also like it because it's much less invasive than going in the front. But anyway I gave that, I give my experience and it was still early back in 2016. Um and I remember I got panned, everybody was up in arms. What are you doing? It's a front procedure only and so on. But slowly people have migrated and some surgeons now doing it in the back and I think that for the right patient it's the right procedure. And then finally we apply it for the mature patients. I think this is remains controversial. There are certain centers that tether anybody who wants to be tethered. And then there are other centers who are very, very strict. I'm I tried to find the moderate position. I have a conversation with the family and I make sure I explain to them all the pros and cons of tethering and the fact that there are two goals. One is motion conservation but the other is growth modulation. I'd like you to have enough growth remaining that you can spontaneously straighten. You can sort of finish off the job, I'll correct you partially and then you do the rest and in so doing you relax the cable and if you relax the cable it probably will not break as readily. But I think in today's world the mature tether is here to stay. There are patients who simply don't want a fusion or at least want to try to avoid a fusion. And I think that's reasonable in the educated patient. That's reasonable. I'd like to sort of finish by talking about when things don't always go right. I think that's an essential part of deciding on spine surgery and the conversation you have with your surgeon and these are the published results on the left and sort of my experience at UCSF on the right. And I think our experience mirrors the national experience except perhaps we haven't had any transfusions. So that would be a difference. Maybe it's because I do it open and I just have a little bit more control um of the bleeding. The cable fracture rate is variable. I think One study said 15%. Another study said higher. I think we're about the same there. We haven't had nerve issues. Post op the published rates are variable but they're not zero. And that may be because when I do it open I see every nerve. When you do it through a telescope, you what we say is you bluntly dissect tissues so you're careful so you don't damage nerves. But you know it's hard to be 100% careful. But anyway there are complications of this procedure and you should talk your surgeon about them. Don't be shy. Um This is a recent study that was relatively um pessimistic about tethering. And I put this in here to remind the public that I've always been very careful and selective in rolling this out. It's new technology and unlike the iphone where you'll stand around in a in a queue around the block waiting for the latest iphone don't do that in medicine. If you're going to take on new technology please take it on carefully so you as the patient, please talk with the surgeon, please educate yourself. Make sure you understand what you're signing up for because we always worry about how we roll out new technology and it should be rolled out carefully and slowly. So this is the mic conclusion. I think that non fusion is better than fusion. I think nobody would deny that even those who dismiss tethering as new. Um And they have natural skepticism of new things. Could not disagree with the fact that non fusion is better than fusion for the spine. I think there is a clear role for tethering. It's here to stay. But these are the things that we need to work on. We still haven't defined the ideal patient. For example must you be immature or can you do it in the mature setting? The timing is critical so that you can have enough growth remaining to complete the correction but not too much growth remaining that you overcorrect and the same thing can be said for the tension, ng enough tension that the child can do the rest. Not too much tension so that the child might overcorrect. And clearly we need a more durable cable. That's the weak link in the system. Once we have that then I think people are going to become more optimistic about doing the procedure. If you'd like to get in touch with us or if you'd like to refer a patient you can call the general number for UCSF which is 415 353 3000. Or you can call our clinic directly and that is 415353 2967. And even more directly you can call my assistant at (415) 353 9384. Thank you. Mhm