 So if you look at the spine, an optimist call it a vertebral column, and it's actually a mechanical marvel, an amazingly complex structure which has 33 vertebra, 7 cervical, 12 thoracic, as dorsal, called by neurosurgeons, lumbar 5, sacral and coxigials, with the 23 inter vertebral disc which are actually pre-sacral. Now the two vertebra, the adjacent vertebra, with their intervening inter vertebral disc, and the joints and the ligaments surrounding make one functional spinal unit. The structure as we all see is a curved structure, where we can see in the fetus life, it is a you know single curve which is kyphotic that is convex posteriorly, but as the child lifts his neck, the cervical spine curves anteriorly which is called a lordotic curvature, and when the child begins to stand and walk, the convexity appears anteriorly in the lumbar region, we call it as lumbar lordotic curves. So the kyphotic curves which are the fetal curves that is retained in the thoracic and the sacral region, whereas cervical and lumbar regions show the lordosis. Now this kind of a curved arrangement actually gives a tenfold ability to resist the axial compression and the loads. Now if you look at the line of gravity which passes through the column, it passes through the dense more to the posterior aspect of the bodies of the cervical vertebra, but as we descend down, it is anterior to the thoracic bodies, that is the gravitational moment is more towards the anterior part here, and when it descends, when we descend down in the lumbar vertebra, again it slowly goes behind the posterior part of the bodies. To begin with, all of us know that the vertebra is composed of the body and the vertebral arch, the vertebral arch has a pedicle and the posterior elements, posterior elements are the lamina, the articulating facets, the transverse processes and the spinous process. The anterior part of the lamina which is actually between the two facets is known as the parts interarticularis, the part which is actually transmitting the bending forces from the posterior elements to the pedicles. And the pedicles are actually the short stout pillars which transmit the force of all the posterior elements to the vertebral bodies. So that is why as we go down, we see that the thickness of the pedicles increases as the load is increasing. Now the parts that is the anterior part of the lamina is again the part which is transmitting the forces is most developed in the lumbar spine and also has more of cortical bone to accommodate these increased forces. And if there is any insufficiency in this cortical bone, this can make it susceptible to the fractures. The spinous and transverse processes are the size for muscle attachments and also they serve to increase the lever arm for the muscles of the vertebral column. The articulating facets which are actually forming the articular pillars for these vertebral bodies and they also form the posterior boundary of the interventricular foramen whose superior and inferior boundaries are formed by the pedicles of the upper and lower vertebra. The anterior boundaries we can see are formed by the posterior lateral aspect of the vertebral body into vertebral disc and the body below. Now this is because the vertebra adhere to the common basic structural design but of course they show regional variations in size and configuration that reflects the functional demands of a particular region. So we start with the cervical region first. So if you look at the cervical spine, the vertebral bodies if we see they have more of transverse diameter and the less of atroposteal diameter, the upper surface we can see is showing the liping forming the ankle joints with the vertebra above. Now if you look at the pedicels, the pedicels which are now projecting postrolaterally and the laminas which are projecting postrolaterally, they are narrow, the spine is bifid here. Now if we go lateral to the pedicel what we see is the foram and transversarium which is the unique feature of the transverse process of the cervical vertebra and is surrounded by a ventral bar, a dorsal bar, the end or this is also known as anterior root or the posterior root which end in the prominence anterior tubercle and the posterior tubercle. The two are connected by what is known as the inter tubercular lamella or the costal lamella. This actually represents the true transverse elements embryologically whereas the rest of the whole thing is from the costal element embryologically. The structures passing through the vertebral foram and are the vertebral artery, vertebral vein and the nerve branches from the cervical thoracic ganglia. So pedicel if we see lies at the crossroad between the vertebral canal which is carrying the spinal cord and the meninges and laterally are the vertebral artery veins and the structures. So any approach to this pedicel one has to take care of the medial as well as the lateral structures. Now this area which we see from behind is the lateral mass which is seen between the superior and the inferior articular facets. Pedical in the subaxial spine is actually very narrow so it is generally the lateral mass which is used for the entry point for the pedicel screws. Now if you look at the facets of this subaxial spine their direction is actually the coronal. They are flat oval directed the superior ones are directed superiorly and posteriorly inferior ones are directed more forwards. So this kind of an arrangement their orientation makes them the rotation in the the movements which we see in this zones are basically flexion and extension around 20 degrees of flexion and extension a bit of lateral bending and rotation which is minimum. Now looking at the comparison of the bodies and the pedicel we see that the body this transverse diameter varies from 17 millimeters to 23 millimeters when we see in the subaxial spine. The antropocidio diameter from 15 to 17 millimeters shows less of a variation the height also remains more or less the same. The width of the pedicel if we see just varies from 5 to 6 millimeters the C7 that is the vertebra prominence may have a little more that is 7 millimeters. The other thing which is important for the pedicel is the angles which it makes with the sagittal plane as well as the the frontal plane. So here we see that the transverse pedicel angle that is if you have the midline and how it is oriented to the midline that is the angle which is making with the sagittal plane. So in the C3 they are directed I mean anatomically we say they are postrolateral but when we are looking from behind when we are looking from behind they are converging pedicels that is they are from the postrolateral they go to the antromedial. So the angle which they make is approximately 43 degrees in the C4 43.5 and then the angle goes on reducing. So by the time it is C7 the angle formed by the pedicels with the body is 30 degrees here you can see the angle which is reduced to the 30 degrees. As far as the pedicel height is concerned that varies from 7 to 7.5 millimeters. Now the sagittal angle that is the direction of the pedicels see normally in the dorsal region they are all facing downwards but when we look at the subaxial spine especially the region of C3, C4 and C5 there is a slight syphilic orientation. So that is why it is the angle we say is in minus because of their orientation which is slightly syphilic because that will decide the trajectory of the pedicel screw while putting through in this region. Coming to the atypical vertebra that is the first cervical and the second cervical vertebra they are it is a ring like structure. So here we have the anterior arch with the anterior tubercle posterior surface bears a facet for the bends and we have the posterior arch with the posterior tubercle posterior arch is slightly longer and bears a groove for the vertebral artery. We can all see a vertebral artery groove and which is overhung by these lateral masses. So lateral masses which we see bears the superior articulating facets. Now here the direction of the superior articulating facet is very unique. We can see they are kidney shaped but the way they are directed this actually permits more of flexion and extension and a bit of rotation and little bit of lateral bending but more of it is flexion and extension because of the geometry of these articulating facets. The lateral masses which bear the foramen if you see the width of the atlas you see it is quite a bit it is around 65 to 75 millimeters in males and in females it is slightly less. So sometimes it is said that the atlas can also be used for sex determination of an individual. Now the if you look at this posterior groove for the vertebral artery because the vertebral artery which has travelled through the foramen transversarium now takes a loop and runs over it and between the two comes the C1 that is the suboccipital nerve. If you look at the I think this fine which I am holding has a kind of foramen which has been made. So this is where the you know when we see the ossification of this vertebra sometimes the you know the margins of these two that is the posterior arch they are raised and these are some ossification defects what we say or whatever it is it is seen in around 12 to 19 percent of the individual this is called ponticulus the atlas posterior ponticulus where which forms actually a foramen for the vertebral artery. So you can see the vertebral artery can go through this foramen even the posterior part of this arch of the atlas around 5 to 10 percent of the people this part is defective. So while approaching these areas okay for the lateral mass screws this kind of information is important. Looking at the dense which is articulating with this it is held by the ligament that is the transverse ligament here. Now the other ligaments which we see on the dense will be the apical ligament from the apex and ilar ligaments from the side which are going to the occipital condyle. Coming to the C2 so this is just the ponticulus posticus I got the picture but I think I have already having it in the spine. Now coming to the other atypical vertebra that is the second cervical vertebra which all of us see here the body of the atlas which we say the centrum has actually gone on to the axis or that is in the form of here dense which has a facet for the atlas anteriorly and a groove for the transverse ligament which it is holding. Now here the direction of the superior atypical of facet of the dense is actually somewhat complementary to the inferior atypical of facet of the atlas vertebra and that this kind of a direction of the atypical of facet actually makes them rotate that is the rotation is in the more in the atlanto-axial joints somewhere around 40 degrees 43 degrees of rotation. Now if we come to the lateral mass area and what we see is the superior atypical of facet and inferior atypical of facet they are not in the same plane as in any other vertebra. So this part is what is actually being represented by par's interarticularis you can see in the vertebra that is the zone between the superior atypical of facet and the inferior atypical of facet is par's interarticularis which actually is considered as a pedicle. So I do not know whether we should dissect it too much that what is pedicle and what is par's interarticularis the medial part of the par's interarticularis can also be called as pedicle but pedicle if we define it is the area which is connecting the vertebral body to the superior atypical of facet. So by definition this is not the pedicle, pedicle is this area that is why I just wrote it here and this is the par's interarticularis. Now what is important here is that in this zone this is the foreman transversarium so the vertebral artery is passing through it the distance of this is very very minimal. The entry point for the screws in the cervical region if we say the lateral distance is the from the vertebral artery is just maybe 1.38 millimeters okay. Now the other thing which is more fascinating here is that the vertebral artery when it's passing from coming out from the axis it just takes a lateral bend towards the atlas that is the foreman transversarium in the atlas and this is the part it is not covered dorsally by any of these structures which normally happens in any of the subaxial spine and this takes a loop and this part is very long and then again takes a loop over the atlas. So this length of the vertebral artery actually allows these rotation movements which are taking place at the atlantoexil joints. If this vertebral artery was not long enough this amount of movement at the atlantoexil joint was not possible. So this maybe the length gives it that much of the leverage to rotate. The importance of the ossification here and the embryology of the axis vertebra is that all of us know that the vertebral bodies are derived from the somites okay. So the part of a somite which is called sclerotome. We have sclerotome, dermatome and myotome. So the sclerotomes which then you know migrate around the notochord and form these blocks and get arranged into a lighter cranial and a caudal part. The cranial part is little less denser as compared to the caudal part. So in the occipital region we have four sclerotomes and first maybe sort of disappears, second, third and fourth they fuse and contribute to the formation of basiocciput, a part of the exocciput that is the tubercles and the part of the arch of the atlas. And now here they say that this part that is the occipital four and the first cervical. The second cervical and the third. The new theory which says is that these three the five, six and seven and part of the four they fuse to form this x, y and z. So the dense which is actually seen here is derived from the fusion of the three components that is the sclerotome five, six and seven and we see that the intervertebral discs have sort of disappeared. So x forms the tip of the axis. So y forms the base of the dense and z may be the centrum of the axis. So if the x and y do not fuse the condition is called the os terminal which we see in the type one type of odontoid fractures and when the y, x, y complex does not fuse with the z we call it as os odontoidium. This is just to show you the relationships of the vertebral artery along the from the coming out from the axis. So this is the journey from axis to atlas and then on the atlas that is the retro loop of the vertebral artery, the retrocondyled loop. So here this is the C1, C2 loop and here this is the only on the posterior arch of the atlas. We can see the posterior loop of the vertebral artery. This is just the angulations here which are actually much more in the C2 where we see that the rostrocordial angle is around 38 to 39 degrees whereas in the transverse direction that is the transverse pedicle angle is around 35 degrees and this may be the entry point for the pedicle mass screw or the pass screw and you can see the relation of the vertebral artery to this area is very very close. As far as the ligaments of this area are concerned the anterior longitudinal ligament which is bounding this anterior part of the vertebral bodies. Now over this continues as what is known as the Atlanta axial membrane and from here it is Atlanta occipital membrane, sort of things out in the middle but may be expanding on the lateral side. Now here we have the epical ligament of the dents and behind that what we have is a cruciform ligament which is having a vertical band and a horizontal band. The horizontal band is the one which I am talking about as a transverse ligament here. Now the PLL that is a posterior longitudinal ligament continues here as the membrane or tectoria and finds it attachment on to the furum and magnum here, the basic occipit actually and the ligamentum flavum which is connecting the laminas here now becomes the posterior Atlanta occipital membrane up. So anteriorly when we are looking so this is the part of the ALL and this is the anterior Atlanta occipital membrane. We can see the ALL has really narrowed here and these are the fissure joints and the ligaments. Now when we cut through the spine and see here we can see that this is the now membrane or tectoria that is a posterior longitudinal ligament which has continued as membrane or tectoria. Cut through the membrane or tectoria we can see the transverse ligament and the longitudinal band. So this makes a cruciform ligament with a superior band and an inferior band, the ALR ligaments and the apical ligaments. ALRs are on the side and apical is somewhere in the middle. The transverse ligament is actually very strong, it is rather stronger than the dense. We say that the dense usually fractures before the even the ligament ruptures.