Osteology – Thorax Muscles and Thoracic Wall

by Craig Canby, PhD

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    00:01 Welcome to this lecture on “The Thoracic Wall”.

    00:05 This slide depicts the learning objectives that you should be able to answer at the conclusion of this lecture. First, describe the osteology of the thoracic wall that is ribs, sternum and thoracic vertebrae and the intercostal spaces.

    00:19 Compare and contrast the movements of the thoracic wall and cavity.

    00:24 Describe the thoracic apertures. Categorize thoracic muscles as extrinsic and intrinsic. Describe the attachments, innervation and actions of the thoracic muscles. Describe the neurovascular structures of the thoracic wall. And then we'll summarize the key take-home messages from this lecture. And then we'll provide attribution for the images that were used throughout this presentation. This is our body map and the thoracic wall will have an anterior aspect to it, a lateral aspect and then we also have posterior structures that are associated with the thoracic wall. So, that will be our focus for the remainder of this presentation. And that we'll begin with the relevant osteology.

    01:15 And so, our focus here will be on the ribs, sternum and thoracic vertebrae. But first, we need to understand the fact that we have 12 pairs of ribs. And we can count those 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and then, more posteriorly, we can see 11 and 12. If we stick with the posterior view, you can see that there are spaces between the ribs and these are termed intercostal spaces. We will have a total of 11 intercostal spaces.

    01:55 Ribs can be classified on the basis of their attachments and whether or not they are true ribs or false ribs. We can categorize ribs as being vertebrosternal, vertebrochondral or simply vertebral. Vertebrosternal ribs are the first seven pairs 1, 2, 3, 4, 5, 6 and then here is 7. At the anterior aspects of the first seven pairs of ribs, you will see these blue bars of hyaline cartilage. They are termed costal cartilage for each rib and they will connect each of the first seven vertebrosternal ribs directly to the sternum. Because of this direct connection between the costal cartilage to the sternum, these are called true ribs. The vertebrochondral ribs would be ribs 8, 9 and 10. And if we take a look here, here is number 8, here is number 9 and then here is number 10. You will see that they too have, on their anterior ends, costal cartilages, but they will then, instead of attaching directly to the sternum, these costal cartilages will connect to the costal cartilage above. So, here's the costal cartilage of rib number 8 and you can see it connects with the costal cartilage of rib number 7.

    03:28 Similarly, rib number 9 intersects or connects with this portion of the costal cartilage, and then the 10th one does so as well. The name for these false ribs would be vertebrochondral because of their posterior attachment to the vertebral column and their anterior attachment to the costal cartilages. The last two of ribs just have vertebral attachments to the thoracic vertebrae, the lower two, and no anterior attachment. So here, we see number 12, here we see rib number 11. They just have posterior vertebral attachments and they do not have a direct anterior attachment to either of the costal cartilages and they certainly do not connect to the sternum. We can also take a look at ribs to best understand some of their osteologic features. And we can classify ribs in this context as either being typical ribs or atypical ribs. We first want to understand the basic architecture of a typical rib and typical ribs will be rib pairs 3 through 9.

    04:51 The osteologic features of a typical rib, and we’re going to focus on these two illustrations here in the image. The typical features would include a head and there are two articular facets to the head of the typical rib. Just distal to the head of the rib, the rib will narrow and for a very short distance, you will have what is known as the neck of the rib, also shown in the illustration above. And then just distal to the neck of the rib, there will be an expansion of the rib and this expansion is known as a tubercle.

    05:32 And you can see this blue-colored area in this portion of the illustration as well as the rib above and that will serve as an articular process for a transverse process of the thoracic vertebra. Just distal to the tubercle, you can see that the rib makes a band and it will be directed inferiorly and anteriorly at this band. This band represents what is known as the angle of the rib. And just anterior to that angle, this is typically the most common point for a rib fracture because this is the weakest point of a rib. And then if you look on the inferior aspect of a rib, you will note the presence of a costal groove.

    06:27 Atypical ribs would be rib pairs 1, 2 as well as 10, 11 and 12. The features of atypical ribs are going to deviate from those that we just went over with respect to a typical rib. And of these atypical ribs, the most unique and peculiar rib is actually going to be rib 1. And we see rib 1 in the upper portion of this illustration and its head will articulate with just one thoracic vertebra. That’ll be T1. It is highly curved and tends to be more shelflike rather than directed upwards and downwards and the top of the shelf presents two grooves. This groove is more anterior to this one and the subclavian vein crosses over rib 1 in this anterior groove. And then lying behind the subclavian vein is the subclavian artery and it will course through the groove located here.

    07:38 If you're very interested in some of the other features that deviate from a typical rib, I would direct you to your anatomy textbook. We probably don't need to overly focus on some of those features that do deviate from the typical ribs.

    07:57 The sternum is another osteologic feature of the thoracic wall. It will lie in the anterior midline. The sternum has three parts to it. We have a manubrium and then the superior portion that we see here notched within the manubrium is the jugular notch. And then we have clavicular articulations here. So, the clavicle on each side articulates at this particular point. The manubrium makes an articulation or joint with the main portion of the sternum and this is termed the body. And then the most inferior component of our sternum is the xiphoid process. And in the illustration, the xiphoid process in this example is bifid and it can come in different morphologies or forms. I do want to point out this area right in through here where the manubrium does articulate with the body of the sternum.

    09:00 And if we shift our attention here to this lateral view, you see the manubrium. You see the point of articulation with the body and you can see that there is a slight angle as a result of this articulation. This is the anterior portion. It is readily palpable on the anterior thoracic wall and this angle represents the sternal angle or the angle of Louis. At this angle, you see a point of connection for the costal cartilage of rib 2. And so, by identifying the sternal angle and going laterally from there, identifying it here in the anterior view and go lateral in either direction, you can then identify the level of rib 2 and then you can count your ribs below that if you have to identify some of the intercostal spaces.

    09:57 Since all the ribs have an attachment to thoracic vertebrae, let’s pause for a moment and look at how the ribs do articulate with the thoracic vertebrae. Many of your ribs are going to articulate with two successive thoracic vertebrae. So, if we take a look at the example here, we have a rib and for the purposes of explanation, let’s say this happens to be rib number 6. One of the facets on the head, the more inferior one, will articulate with the 6th thoracic vertebra as is shown in the illustration.

    10:39 Here is the superior facet on the head of the rib. It’s going to articulate with the inferior aspect of the 5th thoracic vertebra. And then if we look at the tubercle, here we can see the tubercle of rib 6 articulating with the transverse process of the 6th thoracic vertebra. There are some exceptions with respect to how ribs articulate. Ribs 1, 10, 11 and 12 just will articulate with their respective vertebral level. So, rib 1 just with T1, rib 10 with just T10, rib 11 with just T11, rib 12 just articulates with T12. And then the transverse processes associated with thoracic vertebrae 11 and 12, there is no articulation of those transverse processes with the tubercles of the ribs at that level.

    About the Lecture

    The lecture Osteology – Thorax Muscles and Thoracic Wall by Craig Canby, PhD is from the course Abdominal Wall.

    Included Quiz Questions

    1. 1st to 7th ribs
    2. 2nd to 8th ribs
    3. 5th to 12th ribs
    4. 1st to 9th ribs
    5. All are true ribs.
    1. Ribs 11 and 12
    2. Ribs 9 and 10
    3. Ribs 8 and 9
    4. Ribs 5 and 6
    5. Ribs 9, 10, 11, and 12
    1. At the angle
    2. At the tubercle
    3. At the neck
    4. At the head
    5. At the costal groove
    1. 1st
    2. 2nd
    3. 3rd
    4. 4th
    5. 5th
    1. Angle of Louis
    2. Angle of movement
    3. Angle of scapula
    4. Angle of clavicle
    5. Angle of xiphoid
    1. Rib 8
    2. Rib 10
    3. Rib 7
    4. Rib 11
    5. Rib 12
    1. Rib 1
    2. Rib 12
    3. Rib 7
    4. Rib 9
    5. Rib 10

    Author of lecture Osteology – Thorax Muscles and Thoracic Wall

     Craig Canby, PhD

    Craig Canby, PhD

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