 Hello everyone, welcome to this session on osteology of thorax. In this session, we will be quickly revising about the thoracic cage, the various joints in the thoracic cage. Then individual bones also will be covering the sternum, ribs as well as the thoracic vertebrae. So let's begin with the thoracic cage first. So here we can see the specimen of the thoracic cage. So thoracic cage is formed by which bones? The one bone which we can see on the anterior aspect, this is the sternum. Then there are 12 pairs of ribs along with the costal cartilages. Then when we see on the posterior aspect, there are 12 thoracic vertebrae along with their inter vertebral disc. So all these bones are included in the thoracic cage. Now let's see the boundaries of the thoracic inlet and the outlet. So here we can see the upper opening which we can see this is the thoracic inlet. I'll just rotate and let's see. Okay, now let's try to identify the boundaries of the thoracic inlet. So here is the anterior aspect, you can see the superior border of the sternum. Then the medial border of the first rib. Then there will be anterior border of the first thoracic vertebrae. Okay, so these are the boundaries of the thoracic inlet. Let's see the boundaries of the thoracic outlet now. So this opening lower aperture of the thoracic cage, this is the thoracic outlet, it is bounded on the anterior aspect by the referred process of the sternum, then the costal cartilages, then the 11th and the 12th rib, okay, so this forms the costal margin and there will be anterior border of the 12th thoracic vertebrae, okay. All these are the boundaries of the thoracic outlet, okay, thoracic outlet is bounded by the thoracoabdominal diaphragm, okay, thoracoabdominal diaphragm is present here. Similarly, there is one diaphragm present on the thoracic inlet as well that is referred to as cervical diaphragm also referred to as citizen's fascia, okay. And the space in between the ribs, these are referred to as the intercostal space, these are covered by intercostal muscles, okay. Now let's cover the various joints of the thoracic cage. So let's begin with the joint which is formed by the ribs. So if we trace the rib on the posterior aspect, on the posterior aspect the rib articulates with the corresponding vertebrae as well as vertebrae which is higher up, okay. So there is costo-vertebral joint between the ribs and the vertebrae, it is a plain variety of synovial joint, okay. Then the ribs also articulate with the transverse process, there is a part of the rib which is called as tubercle of the rib, tubercle of the rib articulates with the transverse process. This joint is also a plain variety of synovial joint, okay. Now let's trace the rib forward. So here we can see one joint between the rib and its costal cartilage. This is a primary cartilage in its joint. Then we trace the costal cartilages towards the sternum, there is a joint here. This is the chondro-sternal joint. In the chondro-sternal joint, the first chondro-sternal joint it is a primary cartilaginous joint and the remaining chondro-sternal joints are plain variety of synovial joints, okay. Also there is articulation between the adjacent costal cartilages. Up to seven ribs, the costal cartilages they are attached directly to the sternum and below the seventh rib, from eight rib onwards, the costal cartilages are attached to the rib which is higher up, okay. To the costal cartilage which is higher up, so eight, nine and ten, they attach to the costal cartilage which is higher up and this joint is, these are combinations of small synovial joints, okay. Then eleventh and twelfth rib if we see, they don't articulate with the costal cartilage which is higher up, okay. So these are referred to as floating ribs, okay, eleventh and the twelfth rib. Then let's cover the joints of the sternum. Sternum has got three parts, manubrium, body and the zephyrd process. The joint between the manubrium and the body of the sternum, the manubrious sternal joint it is a secondary cartilaginous joint, okay. So secondary cartilaginous joints are referred to as simpices, most of the midline joints are simpices, okay. So the joint between the body of the sternum and the zephyrd process, this is also a secondary cartilaginous joint, okay. In some books it is given as primary cartilaginous joints also but according to the standard books like Grey's Anatomy and Last Anatomy, this is given as a secondary cartilaginous joint, okay. So both joints are secondary cartilaginous joint, simpices, okay. So this was all about the various joints of the thoracic cage. Now let's cover the individual bones of the thoracic cage. Let's start with the sternum first. So here we can see the sternum, we have come from the anterior aspect. Sternum is an example of a plaid bone, okay. Three parts we have already discussed, manubrium, body and the zephyrd process. It has got two surfaces, anterior surface and the posterior surface. This surface is the posterior surface. Then let's study about the specific parts of the sternum, that's the manubrium. Manubrium, if we see, it has four borders and two surfaces. So there is an upper border, lower border and the two lateral borders. Two surfaces are anterior surface and posterior surface. Then when we see the body of the sternum, it also has two surfaces and four borders. So anterior surface, posterior surface, two lateral borders and here is the upper border and the lower border which articulates with the zephyrd process, okay. And the small portion is this is the zephyrd process, okay. Then lateral border if we see, there are articular facets for the ribs. In the manubrium if we see, this articular facet is for the first rib, okay. Then this articular facet is for the second rib. So second rib articular facet, its major part is in the manubrium and small part is extended in the body of the sternum. Then these are the other facets, third, fourth, fifth, sixth, as well as seventh, okay. So for seventh rib, there are articular facets directly on the sternum. Ribs which are below, eighth, ninth and tenth, they will articulate with the cartilage which is higher up and 11th and 12th are the floating rib, okay. Now let's cover about the attachments of the sternum. So here we can see the two rounded attachments. These are the attachments of the sternal head of sternocleidomastoid muscle, okay. And this shows the attachment of the sternal head of pectoralis major muscle, okay. All this area, entire area will be covered, okay. And in the lower part, anterior aspect, these two which are shown, these are the attachments of rectus abdominus muscle, okay. From the anterior aspect, there is rectus abdominus. Let's cover the attachments along the posterior aspect of the sternum. So on the posterior aspect of the sternum, these muscles which are seen here, these are the sternohyroid and sternothyroid. Then this muscle which we can see here, this is the sternocostalis muscle. It is a part of the transversus thoracis group, okay. This group has got three set of muscles. The intercostalis, intime, subcostalis as well as sternocostalis, okay. And on the posterior aspect of the zippered process, this attachment is of the diaphragm, okay. So the zippered slip of the diaphragm is attached here, okay. And what does this blue line represent? This blue line represents the reflection of the pleura, okay. So this is the left side of the pleura, this is the right side of the pleura. If we see the left side along the middle at the level of the fourth costal cartilage, the pleura is reflected towards the left because in this region, the heart is occupied in this region, right. So that's why this pleura is reflected towards the left. Whereas the right-sided pleura difference vertically downwards up to the zippy sternal joint and then it deviates to the right, okay. This is one important relation of the pleura which you need to know, okay. Then relations along the posterior aspect of the manubrium. We see the lower half is related with the arch of the aorta and the upper half it is related with the branches of the arch of the aorta. The three branches, the cipallic front, left common carotid artery, left subclavian artery, okay. And also it is related with the left, the cipallic vein, okay. These structures are important because there's a clinical procedure which is called as bone marrow aspiration in which if the puncture needle passes too long behind, so these structures are vulnerable, okay. And apart from this other applied anatomy with respect to the sternum, if we see there's a condition called as funnel chest, also called as pectus excavatum in which the sternum is depressed and there's a condition called as pectus carinatum also referred to as pigeon chest in which the sternum is protruding forward, okay. Then in cardiac surgery for open heart surgery, midline sternal incision is taken, the sternum is separated wide apart to access the heart, okay. In applied anatomy of sternum, we should also know about this manubrious sternal joint. It is also referred to as angle of louis where many anatomical events take place to name a few of them. There's a junction between the superior mediastinum and the inferior mediastinum. Then if we see the arch of the aorta, the ascending aorta it ends and the arch of aorta begins at this level, okay. Then arch of aorta ends at this level and the descending thoracic aorta begins, okay. Also the trachea bifurcates into the right and the left main bronchi at this level. Then the pulmonary trunk bifurcates into the right and the left pulmonary artery, okay. So there are many anatomical events which occur at this level. So this is also one of the important applied anatomy. And also fractures of the sternum if it occurs, most of the time it occurs at this junction at the manubrious sternal joint, okay. So these are the various applied anatomy with respect to the sternum. Now let's cover the rips, okay. In rips and thoracic vertebrae, first of all we should know that which rips are typical and which rips are atypical similarly for thoracic vertebrae. So let us first list down which are the typical and the atypical rips. Typical rips will have certain features in common and atypical will have certain special characteristic features, okay. So the first rip, second rip, the tenth, eleventh and twelfth, okay. These five rips are atypical. The rest of the rips are typical rips, okay. First we'll see a typical rip at various parts and then we'll cover the atypical rips. For example, I've taken here the fourth rip. So here we can see this is the fourth rip of the left side, okay. When you pick up a rip in exam, you'll be asked about the side determination of the rip for which three dimensions are important, like how you justify the side in the bones of the limb. Similarly, you will have to justify the side in rips. So for anterior and posterior, which point you can say, on the posterior aspect, there's the broad part which is referred to as the head of the rip which is on the posterior aspect, okay. Anterior end of the rip is flat. It will articulate with the caustic cartilage, right. And for medial and lateral, it is very simple. The outer aspect is convex. The inner aspect is concave, okay. And for superior and interior, you will have to see the borders of the rip. Okay, so superior border is a thick border. And when you see the inferior border, inferior border will be a sharp border. Also, there will be a groove near the inferior border, that is the caustic groove should be on the inferior aspect, okay. So once you've identified the side, then you'll be asked about the various parts of the rip. So here is the head of the rip, the neck of the rip. In this broad elevation, this is the tubercle of the rip, okay. And there's a bend here that is the angle of the rip, okay. The shaft of the rip. The shaft of the rip has got the upper border and the lower border as we discussed, okay. The lower border bears the caustic groove which will lodge the intercostal vein, intercostal artery, okay. The relation is V, A, N from above downward, okay. Intercostal vein, intercostal artery and intercostal nerve, okay. That's the relation from above downward in the caustic groove, okay. This relationship is important because whenever intercostal drainage is to be done, it should be done near the upper rip, okay. Because when it is done along the lower rip, these vessels and nerves, they may get damaged, okay. So it should be done close to the upper aspect of the rip, okay. Now let's cover the atypical rip. So all atypical rips will cover in the thoracic cage itself. So here we can see the first atypical rip, the first rip, okay. So here we can see it is the most curved rip as compared to that of all the rip, okay. Other features in this first rip, we can see it is flattened from above downward such that it has got a superior surface and inferior surface and inner border and an outer border, okay. In a typical rip, it had a superior border and an inferior border, okay. But in the atypical first rip, it has got an inner border and an outer border. Then in atypical rips also, you will be asked about side determination. For that again, anterior posterior you will have to see. Then for medial lateral concave and convex part, superior and inferior is a bit difficult in first rip. In general, you can remember the superior surface is rough and the inferior surface is smooth, okay. Superior surface is rough because of the multiple structures which are related here, okay. But at times it becomes difficult to identify. So for that, you can keep the rip on the table such that both ends touch the table, okay. For example, if it is the rip of the right side, you place it on the table as if that rip belongs to you and if both ends are touching the table, that means it is the rip of that particular side, okay. If only one end is touching, that means it is not of that side and you will have to shift it to the other side, okay. So that's how easily we can remember the side determination of the first rip and the various structures related with the first rip are marked here. So here we can see this muscle on the anterior aspect is subclavius muscle. Then there is the ligament on the posterior aspect, costoclavicular ligament, okay. This blue colored dotted structure is the relation with the subclavian vein, okay. And this blue color refers to the insertion of the callinus anterior muscle, okay. And this red colored dotted structure, it represents the subclavian artery, okay. Then there are two other structures on the posterior aspect. There is ceratus anterior muscle. And on the inner aspect here, this muscle is callinus medius muscle, okay. Callinus anterior and medius, both are related here. Callinus posterior will be related with the second rip. So on the inner aspect of the first rip, you will see one projection. That projection is referred to as the callin tubercle for the attachment of the callinus anterior muscle, okay. Then there are various structures related in front of the neck of the first rip. And we see from medial to lateral, the medial most structure will be the sympathetic chain. Then there will be the first posterior intercostal vein. Then there will be superior intercostal artery. And lateral to it, there will be the ventral ramus of the first thoracic spinal nerve, okay. We have the various structures related in front of the neck of the first rip, okay. In atypical rip, the examinal's favorite rip is the first rip. So many questions you may be asked in first rip, okay. Second rip will also look similar to that of the first rip, but its length will be twice as compared to that of the first rip. And there is one characteristic feature in the second rip. There is a tuberosity on the outer aspect of the second rip. And this tuberosity gives attachment to the serratus anterior muscles, okay. And on the posterior aspect, there are two muscles which are related. One is serratus posterior superior. And this muscle is callinus posterior muscles, okay. So this was about the second rip. There are three other rip which are atypical. So here we can see this is the tenth rip, eleventh and the twelfth, okay. Tenth rip will look exactly similar as that of the typical rip. There will be only one difference that will be in the head of the rip, okay. A typical rip has got two articular facets, a larger lower articular facet and a small upper articular facet. Whereas the tenth rip will have only a single large articular facet in the head, okay. That's how you will differentiate tenth rip from the other typical rips. And for eleventh and twelfth rip, in general, if you see, it doesn't have tubercle, okay. Other rips have tubercle because they articulate with the transverse process. Whereas eleventh and twelfth rip, they don't articulate with the transverse process of that corresponding eleventh and the twelfth thoracic vertebrae. So they won't have tubercle. And if you see other differences, the twelfth rip is the shortest of all the rips. Eleventh rip is slightly longer as compared to that of the twelfth rip. And the eleventh rip will show a shallow coastal groove. Whereas twelfth rip won't show any coastal groove, okay. There is one difference between eleventh and twelfth rip. A shallow coastal groove may be visible. In eleventh rip, twelfth rip won't have that, okay. And the anterior ends of both these rips will be pointed, okay. They don't articulate with the rip which is higher up, okay. Let's cover a flat anatomy with respect to the rips. Fracture of the rip is common at the level of the angle of the rip, okay. The most common site of fracture of the rip is the angle of the rip. If in case the rips get fractured at two sides, so that condition is separate to a flale chest in which during inspiration the fracture segment moves inwards and during expiration the fracture segment moves outward. It is opposite to that of the moment of the thoracic cage. So that is referred to as aridoxical respiration, okay. This is also referred to as stove in chest, okay. Then there may be extra rips if an extra rip is present in relation to the seventh cervical vertebrate is referred to as cervical rib, okay. It may compress upon the structures which are near to it and the clinical features will be associated with that. And if the rib is present corresponding to the first lumbar vertebrae, it is called as lumbar rib also referred to as gorilla rib, okay. So this was all about the rips. Now let's start with the thoracic vertebrae. Just like in rips, we saw there are some typical and atypical rips. Thoracic vertebrae has also got typical and atypical vertebrae. So here we can see all the 12 thoracic vertebrae in which the first thoracic vertebrae is atypical and the last four thoracic vertebrae, 9, 10, 11, 12, okay. All these are atypical and the remaining thoracic vertebrae are typical thoracic vertebrae, okay. So let's cover features of typical thoracic vertebrae and then I'll tell you about the atypical features of other thoracic vertebrae and how to differentiate it from each other, okay. So let's take one typical thoracic vertebrae. For example, if I take this, so which vertebrae is this? There's a seventh thoracic vertebrae. It is a typical thoracic vertebrae. So in general when we study about the vertebrae, any vertebrae has got two parts. One is the body of the vertebrae and the remaining part is referred to as the vertebral arch, okay. Votal components are included in the vertebral arch. There is a spinous process, then transverse process, then the articular facets, superior and the inferior articular facets, okay. And this junction here is referred to as the pedical, okay. And the connection between the pedical and the spinous process, this broad plate of the bone, this is referred to as lamina, okay. So all these parts are included in the vertebral arch, okay. And when you see the anterior aspect of the lamina and the posterior aspect of the body of the vertebrae, there will be an opening which is referred to as vertebral foramen, okay. It's almost circular in a typical thoracic vertebrae. And the cardinal feature of a thoracic vertebrae is the presence of costal facets, okay. So here we can see the demi facets. A demi facet is in the upper part, a demi facet is in the lower part. Out of which the upper demi facet will be slightly larger because it articulates with the numerically corresponding rib, okay. The rib which articulates here also will articulate in the vertebrae which is above, okay. So small articular facet is seen in the lower aspect of the vertebrae, okay. So when we say about cardinal feature, that means it is specific for that vertebrae. For example, cardinal feature for cervical vertebrae is presence of foramen transversarium, okay. Is there any cardinal feature for lumbar vertebrae? Lumbar vertebrae doesn't have any cardinal feature. It is identified by exclusion, okay. That means no costal facets, no foramen transversarium. That means it has to be lumbar vertebrae, okay. Now let's cover the atypical thoracic vertebrae. This is the first vertebrae T1 that is atypical. So what are the atypical features of this first thoracic vertebrae? This vertebrae will resemble as that of the seventh cervical vertebrae. The seventh cervical vertebrae has a long horizontal spinous process. So you see the spinous process here. It is also a horizontal spinous process. And the body of this vertebrae will also resemble the cervical vertebrae. If you see a typical thoracic vertebrae spinous process, it is directed vertically downward, okay. Can you appreciate here? Whereas this atypical thoracic vertebrae, it is a horizontal spinous process, okay. And also there is a difference in the articular facet which is seen in a typical thoracic vertebrae that demi facet which has been at the end, okay. And there is one single large complete facet which is seen at the middle and there is a small demi facet along the lower aspect, okay. So this is one atypical feature here. And above the pedicle and below the pedicle the area is referred to as vertebral notch superior and the inferior, okay. The superior vertebral notch is deeper as compared to that of the other thoracic vertebrae, okay. Because in the cervical vertebrae also superior vertebral notch is deeper, okay. So these are the atypical features. So now cover the atypical features of the 9th, 10th, 11th and the 12th thoracic vertebrae, okay. And while differentiating these vertebrae, first of all we should differentiate 9th and 10th from 11th and 12th, okay. How to differentiate these two from these two vertebrae? We will have to look for the facet in the transverse process, okay. 11th and 12th vertebrae don't have facet in the transverse process because 11th and the 12th they don't have the tubercle which will articulate here, okay. So 11th and the 12th vertebrae doesn't have articular facets whereas 9th and the 10th vertebrae they have articular facets along the transverse process, okay. Then when we see the articular facets along the body of the vertebrae in a typical thoracic vertebrae there are demi facets in the upper part and the lower part whereas here there is a single facet, okay. 9th, 10th, 11th and 12th. All the vertebrae have a single facet, okay. What of which the 9th vertebrae has got a demi facet only in the upper aspect? It doesn't have a facet along the lower aspect, okay. So for differentiating 9th and the 10th we will have to see a demi facet along the upper aspect and no facet along the lower aspect that means it is a 9th thoracic vertebrae. In 10th thoracic vertebrae there will be a single large complete facet, okay. That's how we differentiate 9th from the 10th vertebrae. And to differentiate 11th from 12th both have single large complete facet but the position is different. In the 11th vertebrae it is almost in the center and in 12th vertebrae it is shifted a bit downwards, okay. And also there is a difference in the transverse process of 11th and the 12th vertebrae. The 12th vertebrae if you see it has got certain tubercles, okay, similar to that of the lumbar vertebrae. The transverse process of the 11th vertebrae doesn't show tubercles, okay. That's how we differentiate 11th from the 12th vertebrae, okay. And if you see the spinous process of the 12th vertebrae it is resembling that of the lumbar vertebrae, okay, broad spinous process, okay. So that's how we differentiate the atypical thoracic vertebrae, okay. And in exams you may be given ribs along with the vertebrae and you may be asked to articulate them so you should know how to articulate a rib with the vertebrae and various joints formed by them, okay. So we have covered all the bones of the thorax in this session. If you all want PDF handout you all can WhatsApp me at the number which is given above and please do watch other sessions of this YouTube channel, okay. Thank you.