 Okay, so the common method of fixation used in spine surgery is pedicle screw fixation. So this is one of the basic techniques, so you must know about it. This was established a pedicle screw fixation because you can engage all three columns, the posterior, the middle and the anterior column by this one method of putting a pedicle screw in the body. So you cover all three columns, so it gives you the maximum stability is via pedicle screw because you start from the posterior element, you go through the pedicle and you go into the body. So you cover all three columns, so please remember that this is a very useful technique and you must know it because it gives very good stability to the spine, the best in fact, because if you go anteriorly you will be able to reach only the anterior column, if you remain only in the lamina or the transverse process it will be only the posterior column, unless you go through the pedicle from posterior to anterior, you will not cover all three columns. So that is the importance of this technique, that it gives you good stability and it covers all three columns. So you must know where the pedicles are and how to put a pedicle screw. So for all practical purposes I would ask you to forget about cervical pedicle screws, you should do it only when you gained experience, little more experience than now. Because in the cervical spine using a lateral mass screw works very well, because the loading, if you see the loading of the spine, why is it important because the loading of the spine? On the cervical spine the loading is only of the head and the neck, all other structures get attached lower down. So as you go down the spine the loading increases and so the loading is maximum in the lumbar cycle junction L5S1 or the lumbar spine. So the fixation has to be very strong if it is to be done in the lumbar spine than in the cervical spine because the loading is less. That is the reason why in the cervical spine even a lateral mass screw fixation works very well because the loading is less. So you do not really need to do a pedicle screw fixation in the cervical spine, remember that. But in the lumbar spine you do need to three column, you need a three column support because all the body's weight is transferred ultimately through the spine and as you go down the loading is more and more. So the lumbar pedicle screw insertion is the most important, second is the thoracic and cervical you can practically forget about it, it is usually not needed. Now how do you put a lumbar pedicle screw? So this is the spinous process, the facet, the articulating facet, the superior one, the inferior one and then the transverse process, this is the transverse process. So if you draw a line which is just outside the articulating facet, that means here. So this is the facet, so a line just outside, so a line just outside, do you see this line? This is the facet, just outside the facet, a line from going from the top to the bottom, you see that? That line you draw is, you identify the whole transverse process like this and a line drawn right in the middle of the transverse process, do you see that? So vertical line which is just outside the facet and a horizontal line which is in the middle of the transverse process. Now the point at which these two lines intersect is your entry point for the lumbar pedicle. So whenever you want to do a pedicle screw fixation, for the beginning it would be best, it is in your interest to identify the whole transverse process, at least the superior margin and the inferior margin. Identify the whole articulating facet, draw a line, imagine that you can use a cotterie, you can actually use a cotterie, a monopolar cotterie and draw that line on the bone and draw the horizontal line and then see where they intersect and use that point as an entry point. There you need to start, that is one. Second, if you see the attachment of the pedicle to the lumbar spine, there are, sometimes it is directly attached at the same level, sometimes it is going upwards, sometimes it is going downwards. If you see the cervical spine, do you see that? Can you see this? So in the cervical spine, the pedicles are usually going vertically up upwards. If you see the thoracic spine, can you see the pedicle is going downwards? Do you see that? That is the pedicle, this part is the pedicle, it is going downwards and in the lumbar spine it is more or less horizontal but it is more medial, it is going medially like this. So you know the starting point, you know that it has to be angled medially. How much medial? You can say from l 1, 5 degrees to l 5, 20 degrees and everything else lies in between. You can divide it equally 4 to 5 degrees for each level. So starting from 5 degrees medial at l 1 to 20 degrees medial at l 5, you will be fine. And the vertical angle, the best thing is to have an x-ray, interoperative x-ray when the patient is like this and see that you are in the middle of the pedicle, neither too close to the foreman above nor too close to the foreman below. You should be in the, cancel is born in the pedicle because there is a small cancel is born element in the pedicle, most of it is cortical bone. So as long as you are in the middle of the pedicle, angled medially and starting at the right point, you will go nowhere but the pedicle unless there is a distorted anatomy or a tumor which is eaten away the pedicle or something like that. In the same principle of a line drawn just lateral to the articulating facet and the same principle of a line drawn in the middle of the transverse process can be used for all l 1 to l 5. So identify the facet, identify the transverse process, draw line, draw line, where they transact that is the place you begin and how do you begin? First thing is to use the all, awl, all, it is got a sharp triangular point, it is used to break the outer cortex, you break the cortex with the all, you have to otherwise you cannot do it. You see that the direction of your all is generally in the direction where you want the screw to be, that is the medial, etcetera, etcetera, all the angulations everything you taken care of. After you use the all then you use a pedicle finder, there are different names where I use prefer to call it a pedicle finder, it is blunt from the front, sometimes it is angled medial but I use a straight one and with the pedicle finder then you can keep it first vertically, then you can give it your medial angulation and then you can give it the superior or inferior angulation the way you want it to be because if you are at L5S1 you need to go downwards, generally for the above, for the superior lumbar vertebra it is straight down. So with the pedicle finder you, if you are in the cancerous bone you will be able to do it with your hand, you just feel it and put it in, generally you have to cover two thirds of the body, your screw should cover at least two thirds of the body because you do not need a bicoctical purchase over here, you do not need to engage the anterior cortex of the vertebra here because you are going through so much cortical bone in the pedicle that it is a very stable, it is a very stable fixation. So as long as you have covered two thirds of the body that is the length of the screw you need, screw which excludes the head of the screw, just the screw should be that length which you measure starting from your hole to the end at least two thirds in the body. Third thing you must do is once you have made your hole you must take a sound, there is a small thin instrument with a round ball like a disector, it is called a sound, you put it in the hole and you actually palpate all around that your bone is intact all around that you are in the pedicle and you have not reached the wall of the pedicle anywhere, either medially or laterally, superiorly or inferiorly, always use the sound and scrape the walls, it is like you put it in a hole, so this is your hole in the bone, you put your instrument, you scrape the wall from below upwards, you know, you start from here, you should scrape it or if you are on the other wall, scrape the other wall. This is the sound, when you see the tip it has got a round ball, so it will not hurt anything, you scrape the walls all around and make sure that your bone is intact all around, then you are sure that you are inside the pedicle, you have gone into the body without breaching any of the cortical bone and once you have made sure put the screw in, so use the same technique for the other side, the angle will be opposite, this time you medial, again you will be medial but angle towards the other side, because you are on the left, that is the way you make the entry point and now for the S1, the S1 can be a little bit tricky, so there are two or three tricks to identify the S1, the principle is the same, if you see this, this is the articulating facet of L5 and this is the articulating facet of S1, so the pedicle again will be the same thing, a line drawn just outside this articulating facet, but here you do not have a transverse process, so you do not know where your horizontal line is going to be, so the points you use are a little bit different, what I do is, you identify this joint, you dissect all around it, see the whole thing, see the joint till it becomes flat, the surface of the sacrum begins, keep on dissecting the sacral surface till you see the edge of the S1 for MN, can you see this, S1 for MN, so you will be able to identify this whole top of the S1 for MN, so it will be like a hemisphere, it will be like a hemisphere, half a circle because you will expose this whole thing, it will be like half a circle, so take the midpoint of this half circle and draw a line straight up till it reaches the base of this articulating facet, okay, so the line drawn at the base of the facet and the vertical line is from the middle of the S1 for MN, where these two points intersect, that is your entry point for the S1 pedicle, and you can never go wrong with this because you will always find the S1 for MN, you can always see the facet of S1, so the horizontal line is below the S1 facet, the vertical line is at the middle of the S1 for MN, where these two lines intersect, that is the entry point of your S1 pedicle, and remember the S1 pedicle is very forgiving, it is very big, very big, very wide, so you cannot go wrong in the S1 pedicle, if you go wrong in the S1 pedicle that means your grossly, your imagination of the anatomy is not correct, the medial angulation has to be much more in the S1 pedicle because of this shape, you see the S1 is sloping like this, so you have to try and hit the bone here, so that you get the maximum length of the screw inside, do you see this obliqueity, oblique sloping nature of the S1, if you make it not angled to this point, your screw will come out somewhere here, and the length of the screw will be smaller, and the smaller the screw, the easier for it to pull out, so you must aim at the promontory, this is called the sacral promontory, your screw should be angled to the middle of the sacral promontory, so your mediality has to be this much, it is here, and your starting point is here, do you see that, it is almost 25 degrees, sometimes even up to 30 degrees depending upon how the pelvis shaped, so 25 to 30 degrees medially, and now the patient is lying like this, so the sacrum is kind of rising up above the L5, so you have to go downwards and medially, so that is the direction of your screw in the S1 for me, for my side, and from the other side it has got to be downwards, medial, and in the pedicle, so that is S1, there are other ways of identifying the entry point, in many ways, two or three is described, but this I found the easiest, because you can never miss the facet, and you can never miss the S1 for a minute, and if you have these two lines, you will always be inside the pedicle, so that is regarding S1, the widest possible, the largest possible screw you can use, you should in the sacrum, because your construct, 99 times out of 100 your construct ends at S1, and as you know the ends of any construct take the maximum load, so your S1 screw is going to take the whole end load of any construct which you use, so your S1 screw has to be the biggest and the largest and the longest of all the S, which you can do, do that, 6 mm, 6.5 mm, 7 mm if you have, if your pedicle is big enough, hit the promontory, you must engage it to the promontory, so that you get a bi-cortical purchase here, because your construct ends at S1 usually, widest screw possible, 7 mm, 6.5 mm, and the length depends upon how far is your promontory, you have to check that on x-ray, you see there are some principles, there is no hard and fast rule, there are some principles, the principles is never stop at the top of a junctional area, so what is the junctional area, L5 S1 is a junctional area, so never stop at L5, that is the principle, if your fusion is going to extend till L5, it is more logical to extend it till S1, because that is a junctional area, which is the second junctional area, D12 L1, so if your construct is going up to L1, do not stop at L1, cross the junctional area, go to D11 and 12 or up to 10 even, that the principle is never to cross or stop at a junctional area, cross it, because junctional area gets the maximum loading, gets the maximum mobility, that is the principle, but then everything does not run by principle, so it depends upon what you are fixing, if it is a trauma, if it is a fracture, the principles are different, you need to keep the ends together till the bone heals, it is like any other fracture, so you do not need to do a P-lif or a T-lif, all those things are not needed, you need some stabilization till the bone heals, till the fracture heals, so your exposure is not going to be that much, you do not need to do all those things, so your fusion is different, but to maintain that intact thing for 2 or 3 months, you need to go couple of levels above, couple of levels below, but sometimes you can exit the metal also, after your fracture is healed, you can go back in, remove all the screws, to get back the mobility of the spine, so if you see the thoracic pedicles, can you see the angle, it is downwards, do you see that, that is the angle, that is the angle, that is the angle, then it starts becoming straight as you reach D1 and C7, and then it starts going upwards, and the C2 pedicle is almost angle 20, 25 degrees upwards, so have you seen this difference, cervical is upwards, then it starts getting down, down, down, down, thoracic is all downwards, and then lumbar again it starts getting straight, the T12, T11 is almost straight, and for the lower lumbar, it starts getting medial, more medial than downwards, so this difference you have to remember, that the thoracic pedicle screws have to be angled downwards into the body, because you will see the pedicles angling downwards, so that is 1, now the entry point of thoracic pedicle, if you see more or less the principle is the same, you have to see where the facet is, you have to see where the transfer process is, and the same lines hold true here also, except that anatomy is not as good as the lumbar spine, you do not see the facet joints as good as you see in the lumbar spine, in the thoracic spine the facets are one on top of the other, they are not side by side, the facet joints in the lumbar spine are side by side, so you can see them, in the thoracic spine they are this way, so you cannot see them, but if I distract it, that is the facet, can you see that, this is the facet, superior facet, inferior articulating facet, and one gets covered by the other and that is the facet joint, so it takes some time to understand just this anatomy, where is the facet joint, the key is this joint, always remember, so let us start with the most difficult scenario that you cannot see anything, the best thing is to dissect this joint, see the spinous process, keep following, follow the lamina, follow the lamina right up to the facet, what you see as a facet, this is the facet, similarly follow the lower lamina, clear all this away, see the facet, if you distract a little bit, that is the joint between the two facets, that is the joint, so even if you do not distract it, because it is difficult to distract, what you can do is drill away some part of the facet here, drill it away, the moment you drill a little bit or even nibble it away with an up cutting, you will be able to see the joint, you will be able to see the facet below, and then your anatomy will be absolutely clear, and the same relations hold true, you expose the whole thing, you see the transverse process and the transverse process in the thoracic spine, go up towards like this, go up, so you dissect all this soft tissue away till you see this, again the line in the middle of the transverse process, but here the only difference is it is not the middle, it is in the upper part of the transverse process, so your horizontal line, instead of in the middle of the transverse process, it will be at the upper end of the transverse process, that is your horizontal line, and the vertical line is the same thing, you have seen this facet, it is in the middle of this facet, so where this line meets this line, that is the entry point for your thoracic pedicle, simple, never forget that, open the joint, see it, you will never miss it, and then the angles, like I said, the thoracic is going downwards, there is no medial or lateral, most of the thoracic is straight down, so that is the dangerous technique because the thoracic pedicle is not big, so if you do straight down and your entry point is wrong, you will end up in the canal, so there is another way to do it, the in-out-in technique, you do not go to the medial wall at all, if you see, this is the pedicle, this is the transverse process, and this is the body, so you can start more laterally, you can start at the top of the transverse process, go straight down, you will remain outside this canal, see, as long as your angulation is correct, you will go through this transverse process, you will come out in the soft tissue, you will keep going and you will hit the body again over here, and you will get inside the body, if you are medial, you will go into the body, so you are in the bone, out of the bone, and again in the bone, but you are nowhere near the canal, so the neural structures are safe, nothing is going to go wrong, as long as you have taken care of the pleura, because the pleura is attached here like this, so as long as the pleura is taken care of, and that is very easy, take a malleable retractor, place it here like this beyond the transverse process, and you are clean, and then you are in-out-in into the body, away from the pedicle, away from the medial spinal canal, very safe, so whenever there is a doubt, use the in-out-in, you will be in the body, you will engage the bony cortex in the transverse process and some part of the pedicle, and it will be safe, that is a very simple way of thoracic pedicles, but thoracic pedicles, you do not really need them, very, very rarely.