 So, when we look at the thoracic vertebra, out of the twelve vertebra, if you have a look from, let us say, T1 to T12, the T1 is called the atypical and even the T12 also called the, rather from atypical, I will say they were called transitional vertebras, because the thoracic one vertebra has some features of the cervical vertebra, whereas the last twelfth, that is, T12 vertebra has the, I will be using the term thoracic, that is the anatomical this thing and you guys say dorsal. So, the last thoracic, that is, T12 has the features of the lumbar vertebra, especially when we look at the, the articulating facets, okay. The upper facet behaves like a thoracic vertebra, the direction, whereas the lower one is like the lumbar. Now, when we look at there, we again go by the features, that is, when we look at the body. So, the body, the transverse and the AP diameter, they again show the variation. In thoracic region, typically the transverse and AP diameters are generally same, when we look at the ventral height and the dorsal height in the thoracic region. Now, the dorsal height is slightly more than the ventral height. In fact, it's at just 0.8 millimetre go on increasing per vertebra, so that's actually adds to the normal kyphotic curve. The dorsal height being more than the ventral height, slightly adds to that. Even the intervertebral disc is placed such that the normal kyphosis comes because of that height difference, which is very, very minimal, cannot be noticed. The other unique feature of thoracic vertebra, all of us now have these facets, the demi-facets for the head of the ribs and the transverse processes have the facets for the tubercles of the ribs. Then we have, if we look at the lumbar, this thing, now the body size, you can see the transverse as well as the APD, both are increasing enormously. So, looking at the dimensions here, the transverse diameter, that is the width of the vertebra, which in the cervical region was just 16 to 17 millimetre, shows an increase gradual, a steep increase from the C5 and you can see here the T1 vertebra. The width is somewhere around 27 millimetres. Again T2 to T7, the width is more or less not varying much and again from T7 to T12, there is a steep increase in the dimension, that is around 40 millimetres and by the time the L5, that is the last lumbar vertebra we have, the dimension goes to around 46 millimetres. So, this is again just to say the, how the load is increasing on the vertebral body, that is why the dimension has increased. Similarly, the depth also has increased, that is the antroposterior dimension, not so much as the width, but yes there is an increase, a gradual increase and from L4 to L5, maybe there is a little bit of decrease in the depth, that is the antroposterior dimension, but overall the dimensions are so big that this is not really noticeable. So, the maximum depth which can be seen is around 30 millimetre in the last lumbar vertebra. The vertebral body height, though the graph shows that there is a slight decrease up to C6 and then there is a steep increase in the ventral heights and in the lumbar region, the dorsal height may decrease, but here this graph does not show what I was mentioning that the dorsal height as I said in the thoracic region is slightly more, which adds to the normal kyphotic curve and here this, the dorsal height being less can be adds to the laudotic curve of the lumbar region. Now, we come to the pedicle morphometry in these two regions. The dimensions which we are going to see here are the transverse diameter, that is the width of the pedicle, then the transverse pedicle angle, this is the axis of the pedicle and this is the mid sagittal plane. So, the angle, the axis of the pedicle makes with the mid sagittal plane is the transverse pedicle angle. The other two dimensions are the pedicle height and the angle with which it makes with this horizontal or the axial plane, that is the sagittal pedicle angle. Here let us see the pedicle width, so I have already stressed on the fact that in the sub axial spine, the pedicle width may just vary from 6 to 7 millimeters. So, it is a very, very narrow structure in the cervical region, but in the thoracic region if we see the, there is an increase initially from T 1 to T 2, that is around 7 to 8 millimeters and then there is a decline. So, the region of T 4 to T 6, this is the region where there is the pedicles are the narrowest, that is the narrowest region where we have may be even you know slightly smaller than this somewhere around 4 millimeter. So, the pedicle screws in this region the leverage is much more less as compared to the other zones, again after T 6 the depth I mean the transverse diameter of the pedicle is increasing may be around 7 millimeters and then it shows more increase and we can see that at T 12, this is around 8 millimeters and up to L 5 if we go the screw can be 16 millimeter wide. The available space is around 16 millimeters for the screw. As far as the pedicle that is the transverse pedicle angle is concerned, the transverse pedicle angle which is this angle in the cervical region we saw that it was 43 degrees that is they were convergent. If we look from the posterior side they were convergent and there was angle of 43 degrees a bit of increase in the C 4, but then there is a slow decline and even the region of T 1, we can see that the convergence is decreasing now and here we can see the angles are just around 25 degrees as the thoracic vertebra when we see. We go down in the T 4 region the angles that means now this angulation is decreasing and they are coming more or less in line and in the region of T 4 the angle the transverse pedicle angle is around 10 to 12 degrees further and here in the region that is the last thoracic vertebra the angle may slightly even go to the negative side. So that means this convergence is now decreasing and there is a slight minus 5, we say minus 5 here and then in the lumber region again the angle of the pedicles increase that is their direction again changes and they again become convergent. So convergent a bit of divergence and again convergence. So in this region maybe that is the vertebra 11 and 12, if we see the vertebra 11 and 12 I know whether we can separate it out we can see that they are more or less you know in line the 0 degree angle. The sagittal pedicle width this is the height or the sagittal pedicle width now coming to the sagittal pedicle angle this is the positive side and this is the negative side the cervical region they are going cephalid whereas in the dorsal spine thoracic spine and in the lumber especially in the dorsal spine they are all pointing downwards they are all pointing downwards. So if we see the T 1 so this angle is around 10 degrees. So from T 1 to T 12 T 10 T 1 to T 10 this angle remains in this zone that is 10 to 15 degrees descending but after the 10th thoracic vertebra we can see that this descent is reducing and slowly they start becoming more horizontal. The L 1 vertebra this is the L 1 vertebra we can see that the angle has now reduced this downward descent has reduced and the angle has rather become more or less around 2 to 3 degrees and by L 2 and L 3 it is 0 degrees. That means the pedicles are attached horizontally to the bodies. Looking at the laminas and the spinous processes we can see that the thoracic region the laminas are overlapping there is less space in the interlaminar groove and look at the obliquity of the spines. The spines are oblique but more so in T 4 to T 8 after that this obliquity again decreases and T 10, T 11 and T 12 the spines have become more horizontal they are becoming more like lumber. Lumber spines again they are horizontal broad and thick so there is space between the interspinous areas. As far as the transverse processes are concerned they are arising from the junction of the powers and the pedicle. So when we look in the transverse process of the thoracic region they are very broad thick and they are directed more postrolaterally. So when we are approaching them from the posterior side they are more in the operative field because of their direction they are postrolaterally. But as we go down T 11 and T 12 in the T 12 we see that the transverse process is hardly there it is just replaced by three tubercles and from L 1 to L 4 the initially the L 1 spine is thin and is directed more laterally not postrolaterally. So this little away from the operative field L 2 and L 3 maybe they have a little more wider and longer transverse processes and again laterally oriented and L 5 has though a shorter but a triangular kind of a transverse process. It is slightly the shape is different from the L 4. The other feature which the transverse processes here in the lumber region have is the accessory process which is actually giving attachment to those multifidus and other inter-transverse groups of muscles. And this lies just lateral to the process that is the mammillary process which is used as actually as a landmark or you know for the entry point for the pedicle screws in this region. So it is slightly lateral to the mammary process which is on the articulating facets. According to the articulating facets that is the facet joints or the zygophysiological joints as said it. So in the cervical region we saw that they were directed in the coronal plane. So coronal and slightly you know like this. So that means when we have many movements we have we have six degrees of movements. So if the facet is more in the you know coronal or directed like this it can have the lateral bending. And if it is in the sagittal plane then flexion and extension movements are more. And if it is more in the axial plane horizontal plane the rotation is possible. So it is not only one movement there is always couple movements because the geometry is such. So in the thoracic region because of their geometry now let us have a look here because of their angulations in cervical they were more inclined at 45 degrees. Now the first one the the geometry of the C1 C2 were slightly different. So if you look at all these movements so this solid line is showing flexion and extension which we can see is 25 degrees here reduces again may be more and then reduces here. The lateral bending is these dashed lines and axial rotation is we can say dots. Now overall we see that the orientation of the thoracic facets is such that all movements are limited. Not only may be just because of the facet but there are other factors like the spinous process they are oblique they joint capsules are more tight which are more relaxed in the cervical and the lumbar regions the rib cage ok. So these factors may be restrict these movements and even the disc height the inter vertebral disc height. So what is available motion in the thoracic region is that there is a bit of axial rotation around 6 to 7 degrees, bit of lateral bending which is again around 5 to 6 degrees and flexion extension is quite reduced because definitely they do not have this sagittal orientation to undergo these movements whereas the flexion extension movement if we see was much more in the region of the cervical region where more in the the atlantooccipital joint decreases at the C2, C3 level but again in the subaxial spine we see an increase in the flexion and extension movement. Rotation being maximum at the atlantoaxial joint because of the geometry here around 43 degrees. Now when we look at the orientation in the lumbar region, lumbar region how they are oriented they are more sagittally. If you look at these facets see that they have a more sagittal comment and a bit of the frontal the coronal component. So that is why the flexion extension movement is much more around 15 degrees of flexion and extension in the lumbar region. Lateral bending yes but axial rotation is completely very very minimal because there is no horizontal component in these facets. According to the ligaments and before that just this thing about intervertebral disc all of us know that it is a nucleus pulposus and annulus fibrosis and the annulus fibrosis which is having fibres directed in oblique directions they are actually at angles to each other. Every layer has an angulation with each other and this is designed such that it actually resist all the tensile forces. The nucleus pulposus is designed to resist all the compressive forces whereas the annulus fibrosis the orientation of the fibres is designed to resist the tensile forces not also this but if you look at the composition what are they actually made up of? The water the proteoglycans and the collagen fibres. So it is the content which varies in these components. So water content is more in the nucleus pulposus so it is more hydrophilic so can get compressed and it actually behaves like a sponge. So the intervertebral disc it not only acts as a shock absorber but it also increases the available range of motion. The facets decide the plane of motion or the kind of motion whereas the intervertebral disc actually decides the range of motion in a particular this thing. So if you look at these intervertebral disc in the cervical thoracic and lumbar region you can see that this actually the cervical disc around 3 millimeters and slowly by the time it is the lumbar region it is 9 millimeters. But still it is not the thickness of the intervertebral disc it is the ratio of the intervertebral disc to the vertebral body height. So this ratio actually decides the range of movement in a particular area which the ratio is highest in the cervical region followed by the lumbar region and then least in the thoracic region that is why maybe more mobility in the cervical and lumbar regions and thoracic region is more stable. So this intervertebral disc which is actually if we see in this coronal plane has 3 components the nucleus palposes, the annulus fibrosis and what we have is here are the vertebral end plates. These vertebral end plates are covering the surfaces the superior or the inferior surface of the adjacent vertebral bodies and the vertebral end plates actually have more of the cartilaginous component is much more and the part which is facing this area has more of fibrocartilage and the part which is away from here has more of high line cartilage which anyway over the age will get replaced and the entire thing will get the fibrocartilage. The collagen fibres in the annulus fibrosis are more of type 1 and this has more of type 2. Again to do with the kind of forces they are resisting so type 2 have more ability to resist the compressive forces and type 1 have the ability to resist the tensile forces here. The vertebral end plates actually if you see do not cover the annulus fibrosis completely. It is more peripherally that these fibres of annulus fibrosis are actually joined to this ring epophysis you know they find there they hold on to the bodies on the sides. And actually if we see it is not very when we look at these structures it is not so easily demarcable it is only the center part of the nucleus palposes and the most peripheral part which can be distinguished clearly. But in between there is no like clear demarcation in their structure. Also if you look at the disc in the cervical region the annulus fibrosis is actually a kind of you know a crescentric ring more anteriorly. It is not covering the disc posteriorly okay so which may be you know reason for the disc prolapse in this area is more postrolateral deficiency is always more because PLL is protecting it and if you look at the shape of the disc in the lumbar region the you know it shows a concavity. So the annulus fibrosis fibres if they show this concavity so they have a more ability to stretch you know so that is why the and it can be said is bigger and here they are more elliptical so the posterior stretching is lesser as compared to the lumbar vertebra. And the this area is supplied be the sinus vertebral nerve the sinus vertebral nerves are nothing but the recurrent branches which are coming from the the ventral ramus which also has the somatic as well as the autonomic component that is by the gray ramiocomunicant is which are supplying these parts of the intervertebral disc. So the disc prolapse so these are the structures apart from the nerves we do have the arteries in this which get affected. The ligaments antirelongitiminal ligaments which are actually thicker opposite the vertebral bodies as compared to the intervertebral disc but this ligament if we see has 2 to 3 layers they are adherent to the intervertebral disc if we see they are in 3 strata so the superficial strata which will connect 3 to 4 adjacent vertebras the intermediate we can connect the 2 to 3 and the deep one will just connect the adjacent vertebra. Now when the vertebral column is if we see the extension movements anterior is running like this so what happens is when we extend so this ligament gets stretched and when the spine is flexed this ligament is lax anterior longitudinal ligament is lax but if we see during flexion it is only this ligament which is lax but all the posterior ligaments that is the PLL the facet joints inter transfers the ligamentum flavum inter spinus and supraspinus they all get stretched. So extension movement is only limited by the ALL and the flexion movement is limited by all the posterior ligaments which are actually the posterior ligament is complex. Ligamentum flavum is unique in that it has high amounts of elastin and has can be stretched up to 80 percent without the damage and it is most strong in the lower thoracic and the lumbar regions. Now if you look at the effectiveness of a ligament how effective a ligament is so that depends upon its morphology and its lever arm morphology by morphology I mean the content or the strength that is if we measure the failure strength of the spinal ligaments in various zone that is the tensile load carrying capacity. So if you look at the ALL this is ALL PLL ligamentum flavum capsular ligament and cervical region. So in the cervical region the failure strength of the capsular ligament that is the one covering the facet joint is much higher. So if this facet this capsular ligament the failure strength is much higher as compared to the other ligaments. So it is very important to preserve these capsular ligaments. Coming to the thoracic region the failure strength of the ALL is much higher as compared to the other. Overall definitely thoracic and lumbar region the all the ligaments have higher failure strength. Lumbar region we have ALL then we have PLL ligamentum flavum capsular and the interspanus ligament. So this is just about the failure strength. But when we look at you know the lever arm that is the distance of these ligaments from the instantaneous axis of rotation which passes through the in the normal condition which is passing through the posterior part of the vertebral body. So we can see that the lever arm of the PLL is lesser as compared to the ALL ligamentum flavum capsular and interspanus ligament. So that means a ligament which has you know a higher lever arm but is weak but has a lower failure strength but its contribution to the spinal stability will be much more because of the the wide I mean the longer lever arm its contribution becomes much more. So a very strong ligament that functions through a relatively short lever arm may contribute less to the stability than a weaker ligament which is working through a longer lever arm. So even interspanus ligament is very important as far as this contribution to the stability is concerned. But in the cervical region because of the failure strength of the capsular ligament is very high though it has a short lever arm it definitely contributes a good amount to the stability of the cervical region.