 So, let's come to indications and technical aspect of posterior C1, C2, C3, we all know this. So, I will just you know just to complete the list is mobile, Atlantic, dislocation we all know this. We must also be aware of the fact that sometimes with osodentoidium, there is a retrolysis of the os and this means that you have to position this patient in a neutral position. Can we put in a flex position or an extended position? He has to be in an absolutely neutral position, you have to make sure about this and every os you must consider as being hypermobile. Then fixed of course, whenever you are doing transoral or something and when you look at a very interesting thing I will tell you, we actually saw this, this was published in JNS a long time ago that they are completely different entities, mobile dislocation and fixed dislocations are completely different entities and you can actually make this out by doing by a study of the facet joints, mobile dislocations will always have symmetrical facet joints and fixed Atlantoexil dislocation will always have asymmetrical facet joints, always there will be fusion, there will be occipitalization of atlas, C23 fusion, asymmetrical joint they are completely different entities. I think mobile dislocations are because of ligamentous laxity and fixed dislocations are actually because of bony asymmetry at the facet level, so they are completely different entities. And then of course, carry malformation, one small point is that every carry malformation that you see, please do a dynamic flexion extension study, look for Atlantoexil dislocation. A lot of times I have got so many patients in whom somebody has done a posterior decompression and has not done and not looked at the Atlantoexil dislocation and later on they come back with severe myelopathy and progressive quadriperesis, so you must always look for Atlantoexil dislocation. If there is Atlantoexil dislocation, don't forget about carry malformation, address the anterior aspect. If it is a mobile dislocation, address the anterior aspect by doing a posterior fusion with reduced Atlantoexil dislocation. If it is a fixed one, then do a transoral surgery or whatever or even a distraction whatever you want to do, but you must make sure that the anterior compression is relieved, forget about carry. And then sometimes with severe torticolors, you might need to stabilize these in lots of problems. And then of course, basilar invagination, I think you know about this classification where basilar invagination is divided into two groups. One is where there is a straight central invagination. And there is another group which is basilar impression, where what is happening is that if you look at all the conventional lines, the odontoid is not higher than the macros line, which is from the anterior margin of the foremen magnum to the posterior margin of the foremen magnum. And yet there is basilar invagination with severe cervical medullary kink because of platybasia and the whole foremen magnum, actually bony part of the foremen magnum actually invaginating inside. So you must be aware of these two entities and treat them accordingly. It's just a small thing. And of course, any transoral surgery, you need posterior stabilisation. And of course, all types of odontoid fractures, when you have these odontoid fractures, you have to again stabilize. So I'm just telling you the indications for posterior stabilisation. And then we have tuberculous rheumatoid. And one small thing about rheumatoid arthritis. This was during my Commonwealth Fellowship. I worked on rheumatoid arthritis. And this was published in neurosurgery. And we found that whenever we've done a small segment fixation for rheumatoid arthritis, it has never worked. It has always failed. So if you have a patient rheumatoid arthritis with atlantic axial dislocation, and we are getting more and more patients like this, please do a complete long segment fixation. At least two levels above and one, two levels below. Otherwise, this is going to fail, right? So of course, we all know about how we plan dynamic x-rays. But one important thing is CT angio, now we do for every patient. Every patient, we do a CT angio. And now we are picking up more and more patients where vertebral artery can get injured. So you must make sure that you preoperatively assess the vertebral artery and make sure that there's no injury to the vertebral artery during surgery. And I'll tell you what are the variations that you are likely to get. So coming to C1C2 fusion, we have this classical subliminal fusion. Everybody's done it. This worked wonderfully well in children. I mean, I would still recommend them for children. Whenever you have a very young child, lateral mass, and all that is a big mess, it's very simple to just do a subliminal C1C2 fusion. So what are the advantages? One important thing when you're doing this fusion is that atlantoaxial dislocation has to be in reduced position. So how do you know it's in reduced position? You can use a CR, but then it's very difficult. The only thing is if you are passing a subliminal wires and you find that there's not adequate space there. There's not adequate space there. The joint is in dislocated position. It has to have adequate space. So if the dura is getting compressed, there is a go very slow. Go very slow. Don't try to manipulate. Just go very slow if there's not adequate space. That means it's in dislocated position. You must make sure that this is done. And the other thing is one important thing which most people don't emphasize is that when you are doing a C1C2 fusion, you must be prepared to change position of the patient. Change position of the patient. Immediately extend the head a little. You're not getting space. Extend the head a little. As soon as you do that, you will find that you are getting enough space. So be prepared to immediately manipulate the head a little. Come to the head on the table. You don't have to re-sterlize anything. You just, with your drapes, you just hold the head, ask him to loosen it. Just extend the little. You will start getting space there. Small thing. And then the very important thing is please estimate the C1 posterior arch and C2 laminar distance. This is very, very important. But what happens is that if the distance between the C1 posterior arch and the C2 is too long, then when you are putting those sublaminar wires, the loop becomes longer. The greater the distance, the longer are the loops of the wires, and which means that they will cause sublaminar compression. So if you want a good fusion, the C1 posterior arch and C2 laminar have to be close together. If they are not close together, then the loop becomes long inside. And that's where sublaminar compression comes in. People don't think about these small things. When they are actually doing it. Then, of course, sometimes, this is a big issue. What happens is that the movements of the neck are never in sagittal plane. They're always coupled. You understand? They're always coupled. Every fine movement is coupled. So one movement will be associated with another movement. Now what happens is that if there is a little tauticalness, which is very common in these conditions, then you think that, say, for example, this is C1 and this is C2. I mean, C1 anterior arch and this is posterior arch, supposing. So you think they're moving like this, right? They're moving like this. Or maybe they're moving like this. But they're not moving like this. They're moving like this, right? So this moves like this in flexion and moves like this in extension. Now what happens is when you look at it in two dimensions, you see that this appears to be close together. See, if you look at only two dimensions, as soon as this becomes, this appears to be close together. But actually, they're not in close together. So if you angulate it like that, it appears as if they're close together. And you think that there has been a reduction, but there has been no reduction. What is happening is just that the plane has changed and you are seeing in two, visualizing in two dimensions what is present in three dimensions. Are you understanding? The second very important place where you think it's a mobile dislocation, where actually it's a fixed dislocation. And that second point is whenever there is an angulation, any kind of tauticalis, when you are doing a CT sagittal reconstruction, you are not actually getting the right plane in flexion extension. Once you are getting this plane and the second time you are getting another plane. And at that point, because the arch is like this, here you are getting this plane in axial image and here you're getting this plane, right? So you think it is reducing, but it's not reducing. The planes are different in flexion extension simply because there is an angulation. These things you don't look at. So how do you get a very good idea that it's not in dislocation, that it's not mobile? You look at the joints. If the joints are asymmetrical and you have a doubt about reduction, right? Then there is no reduction. Number one. The second is look at the posterior arch of C1. If the posterior arch of C1 is not well formed, the joints are asymmetrical. And you have a doubt about reducibility. They are not reducible. Is that clear? Is that clear to everybody? So the problem with posterior wiring is that it's biomechanically very, very weak. And axial movements are especially not preventable. Axial movements are especially not preventable. This is very important. So when you look at the transarticular techniques, it's very stable. But with asymmetrical joints, there is a risk of vertebral artery injury. And if there is any cervical thoracic carfoses, very difficult to perform this. And another problem is that redo insertion is very difficult. So once you have decided a trajectory, that's it. It's fixed. So it's like gone out of vogue. Not many people are using it now. So now we come to the technique which you can call as Gouel's technique. We like to call it Gouel's technique, but all Europeans want to call it the Hans technique. So what you do is you put a plate or you can put polyaxial screws with a rod. And one goes into C1. And so we focus on this because this is the one which is most adaptable and one which is most practical in today's circumstances, I think. So it has very high fusion rays. It does not require a preoperative reduction. There is no subliminal passing of wires anywhere. And you can put multiple trajectories or screws without any problem. And occipitose C1 joint is not compromised. It's only C1 C2 joint which is there. There's a high margin of safety with any altered anatomy, some vertical joints and asymmetrical joints. And it is easily integrated into longer occipitose cervical constructs. Say for example, later on, you want to revise it into an occipitose C3, C4. All you need to do is to remove the rod, put in more polyaxial screws, and then make it longer. So that is why it is the most useful technique to work with. But of course, there are some contraindications. If there are fractures, the lateral mass of atlas in excess, the other thing is aberrant cores of the vertebral artery. Sometimes what will happen is that the vertebral artery will not pass through the foremen transversarium of C1, and it angulates across the posterior joint, C1 C2 facet joint. That's a very, very dangerous situation. You must make sure that that situation doesn't exist. The second is, developmentally, there is a first intersegmental artery. So rather than the vertebral artery, that artery exists, which you can actually see on an angiogram, CT angio, and you know that. The third problem is that there will be a very low lying pica. A low lying pica arising from the vertebral artery at the level of the foremen magnum. Careful, very, very careful. Just look at it. You must be aware of these things. If you are aware of these, you will not cause a vertebral artery injury. And of course, if there is tuberculosis or rheumatoid erosions, whatever you want to do. So now, Nelson and Napoleon. So coming back, so let's look at the anatomy. So you have the anterior tubercle, the C1. And then you have the facets on this side. You see the angulation. You see the angulation. So now, where will you put the pedicle screws? You can only put it like this. There's no other place. You can even put bicoctical screws. And what is the angle? Say how much, five to 10 degrees, right? So what is the thing? Just five to 10 degrees. And what is the best on radiology? What is the best target to anterior tubercle? So the target is anterior tubercle, going to the lateral masses, five to 10 degrees, and a little upwards, right? This will take you to the anterior tubercle. That's passing screws through C1. That's your trajectory of a pedicle screw C1. You will never injure the vertebral artery which is lateral to you. Never, never. No question of injury vertebral artery. Of course, you have to look at those variations, right? When you look at the posterior part, posterior part, you see that this is all you get. So this is the inferior arterial process of the, this is all you get. So what you can do is you can also drill a little bit of the posterior arch here. It's very safe. When you're dissecting C1, just make sure that you are not dissecting along the superior border. Always, any time, if you ever do a C1, C2 fusion, there's no need to expose the upper margin of C1, right? If you stay here and below and expose C2 also, you will never injure the vertebral artery. So never go beyond the lateral margin of the lateral mass and the facets. Never go beyond the upper border of C1 arch, right? And just make sure your trajectory is proper. You will never injure the vertebral artery, right? So this will be always lateral to you, permanent transversal. Is that clear? Coming on to the C2. There is hardly any difference between pedicle and, you know, parse. So, I mean, if you ask me, what is pedicle and what is parse? So pedicle would be probably, probably, I may be wrong, but probably it will be this segment. And parse will be this segment, right? Now the easiest to manage is parse. You can put in a long screw there, right? So therefore, the very simple technique is, draw a line from this spinous process, draw it like this, right through the midline, draw a line along the parse through the midline, right? And that point of intersection is your point of entry. But it really doesn't matter. What matters is the direction and how do you control the direction? Just look at the medial border. You can easily make out at the viewer. Just make sure where the lateral border is and just stay in the midline of the border. What is your angulation? As parallel to the parse as possible, right? Or you can be as parallel to the superior articular process as possible. So what will be the approximate direction? I wouldn't say it is 40, but it's about between 20 and 25. So 20 and 25 medially, 20 and 25 medially, 20 up, right? And following the medial border of the parse or lateral border is difficult to follow because you have the vertical artery right next to it. So just follow the medial border. This will just get you. Is that clear to everybody? You can put in a long screw, you can put in a 24 mm screw into it. No problem at all. Vertical artery never gets injured. The vertical artery is always lateral to it, right? Only thing is you have to make sure that you define the medial border and follow it along the angulation of the parse. Clear? Everybody can do that? Yeah. So therefore, what is the four prong safety advice when you're doing a C2 fixation? One is medial border, okay? Don't go medial to the medial border, follow the... The second is lateral border. Don't go lateral to the lateral border, right? What is the third advice? Stay along the direction of the angulation along the parse. And the fourth is you have a hint from the superior articular process of the C2. So the four prongs will get you very safe. I don't think any of us uses this awl and tap and I think we just use a B1 cutter and just go like that. We don't actually, we never use this awl and tap. And even if you don't have a C arm, it doesn't really matter. Now, when you're distracting, this is a very important thing. One is that here, when you're following the parse, you will actually come to the... Now, distraction is another point which I thought I should mention. When you're following the parse, the best way to reach the joint here is to follow the parse. Just follow the medial border of the parse. Don't go to the lateral border. Just follow the medial border of parse. Now, you will get the C2 nerve root. Just cut the nerve root. I mean, there are several studies which show that it really doesn't make a difference. So just cut the nerve root. Don't think of retracting it up and down initially. Just cut it. Once you cut it, then you will see the facet joint clearly here. And having seen the facet joint, you can, it will, if there is dislocation, the facet joint will be already open. And this is known as the, I told you about the naked facet sign. So whenever there is dislocation, the facet joint is already open. You can actually see it open. And once you see it open, then all you need to do is to put the deceptive, slightly wider deceptive inside and rotate it like that. It will open up. So it's not a difficult thing at all. It's very simple. Only thing is just make sure that you don't go lateral to the lateral edge of this point. That's the only thing you need to look at. So I already told you about this. 5 to 10 degrees medially. And about 20 to 20, 30 degrees upwards and medially. It will get you there. So these are some, this is the way. And how much do you want to go? Go as much as you can. You can even take a bicoartical purchase at C1. And even at C2, you can go anterior. There's no problem. 22, 24 mm, no problem. You're 16 to 18 mm, no problem. Just one or two points only about the occipitocervical fusion. So we have so many types of occipitocervical fusion. I won't get into all the details. You already know them. There's only one point that I like to mention. One is when you are actually doing this occipitocervical fusion by creating this artificial arch business. One important thing that you must remember in case you're doing it, that you must make sure, that you must make sure that this C2 is close to the occipit again so that the loop is not too high. And the other very important thing is please just remove the posterior margin of the foremen magnum. This is not mentioned, okay? But it's a practical point. If you don't remove it, then the loop of the wire goes inside. So just make sure that you are removing the foremen magnum so that this loop goes on moving distally from the cord. This is a small point that you need to look at. And when you are actually doing a contour rod, if you're doing a contour rod stabilization, supposing you don't have those rods, I mean it's almost outdated now. But if you are doing it, please make sure that these rods, these screws are well tightened. Because what happens is that there is telescoping of the rod between the loops of the wires. So this is something that you really need to look at when you're doing a contour. This is the commonest complication which results in instability. The rods move back and forth between the commonest problem. You understand? This is something you need to do. And finally, the occipital fixation. When you're doing an occipito fixation, then what happens is you must remember the anatomy of the occipital bone. There's an internal occipital crest which is the thickest part. The problem is just below that is the occipital sinus. Just below that is the occipital sinus. And sometimes it's a very prominent sinus. Then there may be a CSF leak. That's another problem. But you need a bichortical purchase here. Don't worry about bleeding from the occipital sinus. Don't worry about CSF leak. Here you need a bichortical purchase. Because the monocortical purchase will just come out. So here you do need a bichortical purchase and in the center where there is an internal occipital crest. Nowhere else is it stable. The only point where it is stable is the internal occipital crest. So even if there is a little bit of venous bleeding, it will automatically stop when you actually put this close. Is that clear? Now coming on to the subaxial spine. From C3 to C6. Here it's a very interesting situation. The foremen transversarium has actually moved medially. The foremen transversarium and move medially. And this is particularly very small here. So what do you need? You need this for stabilization. So what you do? Rather than going medially, C3 to C6, what you do is the same 515 to 20 degrees upwards and laterally along the lamina. So stay along the lamina 15 to 20 degrees upwards and this is your trajectory. You see the vertebral artery will never be injured by this. Never. And it has to have a biquarticle purchase. So C1, C2, medial and C3 to C6 lateral. Vertebral artery will never get injured. Is that clear to everybody? So that's all. Thank you so much.