Thoracic Skeleton

00:01 The thorax is home to many interesting and important structures.

00:05 But before we can talk about those structures, we have to talk about the bony elements that enclose them.

00:12 Particularly, we're going to talk about the sternum and the ribcage.

00:16 The sternum is this bone found right along the anterior midline that's broken up into three parts.

00:24 We have a Manubrium. We have a body.

00:29 And at the inferior edge, we have a xiphoid process or xiphi sternum.

00:35 And that xiphoid process you might notice looks a little pointy.

00:38 That's because long ago when people used to use swords, it looked to them like the sternum was an upside down sword.

00:45 In fact, xiphoid means sword like and manubrium means handle.

00:50 Speaking of the manubrium, there's a little feature we want to point out and it's that little divot along the superior edge.

00:57 That's called the jugular or suprasternal notch.

01:01 And that's a landmark that's usually pretty easily palpated during a physical exam.

01:07 These parts of the sternum have joints with each other, although they're not the typical joints you might think of.

01:12 These are synarthrosis meaning there's really no movement between them.

01:16 But we have a joint between the maneuver human body called the manubriosternal joint also called the sternal angle or angle of Louis.

01:25 And then a joint between the body and xiphoid process called the xiphisternal joint.

01:30 And the fact that the manubriosternal joint has three total names is kind of a clue that it's important.

01:35 And it is because it's the anterior most projection and therefore pretty easily palpated all along the sternum, and it's also where the second rib attaches.

01:46 So it becomes a useful landmark on physical exams.

01:49 The sternum also interacts with some other bones, including the clavicle.

01:54 So the clavicle joins the manubrium at the sternoclavicular or SC joint and then the costal cartilages are the cartilaginous ends of the first seven ribs attached to the sternum at something called the sternalcostal or sternalchondral joints.

02:14 Costal referring to rib.

02:16 Chondral referring to the cartilaginous portion of the rib.

02:20 Speaking of ribs, most people have 12 pairs, and they're numbered from superior to inferior 1 to 12.

02:30 And as we're already alluded to, as they come around anteriorly towards the sternum.

02:35 They turn from bone into cartilage, and we call these the costal cartilages.

02:41 And it's great that the ribcage is very strong and protective and protects the structures that lie underneath it.

02:47 But there are still structures that need to pass in between the neck and the thorax.

02:53 And they do so through an opening called the superior thoracic aperture or the thoracic inlet.

02:59 And this inlet aperture is bordered by the T1 vertebra, the edges of the first ribs, and the manubrium.

03:09 Similarly, there's an opening at the bottom called the inferior thoracic aperture.

03:16 And those borders are the T12 vertebra, the 12th rib, and those cartilaginous ends of ribs 7 to 10.

03:26 And these xiphoid process anteriorly.

03:31 And because these cartilages all form a pretty prominent inferior border, sometimes we just refer to this as the costal margin.

03:40 Talking a little bit about the ribs in greater detail, we sub classify them as being true ribs if they're the first through seventh ribs, because they attach directly to the sternum.

03:52 And then we say ribs 8 through 12 are false because they don't.

03:57 Furthermore, we call ribs 11 and 12 floating ribs.

04:03 Now that's in contrast to ribs 8, 9, and 10 that actually attach to each other and then eventually up to the seventh rib via interchondral joints.

04:14 So they at least have an indirect connection to the sternum.

04:18 So far, we've been focusing on the anterior aspect of the ribs, but they go all the way around posteriorly to meet up with the vertebra.

04:25 And the vertebra will be covered in the back section.

04:28 But right now we're just going to look at a transverse view to where we can see the vertebral body and the transverse processes.

04:37 The part of the rib that interacts with the vertebral body is the head of the rib.

04:42 And then the little bump that interacts with the transverse process is called the tubercle of the rib.

04:48 And in between, we have something called the neck of the rib.

04:52 If we go along a little bit laterally from there, we see that the rib takes a sharp turn and where it does so we call that the angle of the rib where these bones interact, we have joints.

05:06 And between the tubercle of the rib and the transverse process, we have the Costotransverse joint.

05:12 And between the head of the rib and the vertebral body, we have the Costcovertebral joint.

05:17 And these are true joints or synovial joints that have a lot of movement.

05:22 But because there's two of them here, it provides an added layer of stability to the ribs.

05:30 And the last part of the rib we'll talk about is this linear indentation along the inferior interior edge, called the costal groove.

05:38 And we'll see later when we talk about the intercostal space, that's where the neurovascular structures in this area are going to run.

05:47 Now, for the most part, ribs are just how we describe them, and they're pretty similar to each other.

05:52 But certain ribs have some unique features that are worth pointing out.

05:57 For example, the first rib is really close to the neck.

06:00 So it's an ideal location to have some attachments for neck muscles.

06:04 And in particular, there's a little bump called the scalene tubercle on the first rib, which is where the anterior scalene muscle attaches.

06:13 And just anterior to that is a groove for the subclavian vein, because that's where the subclavian vein runs, and posterior li to that muscles a little groove for the subclavian artery because that's where the subclavian artery runs.

06:28 The second rib is also pretty important, because we already mentioned it as a useful landmark because it's where the sternal angle is located.

06:37 And we can palpate that, and it's good to know where your second rib is because usually can't palpate your first rib because it's usually hidden by the clavicle.

06:47 And it's the sternal angle that you're going to be looking for when you're really trying to number your ribs.

06:53 Really rib number two, not rib number one.

06:57 The second rib still close to the neck, and it has attachment points for neck muscles.

07:02 In this case, it has an attachment for the posterior scalene.

07:05 Although, it's usually obscured by the serratus anterior muscles.

07:11 The 12th rib is another weird one because it only has a single articular surface.

07:17 And it only articulates with the vertebra at the head, meaning it doesn't have any other features like a neck, a tubercle, an angle or even a costal groove.

07:26 Now, 12 pairs is the most common arrangement, but people are going to have more or less or in fancier terms we say supernumerary or infranumerary ribs.

07:38 For example, about 1 in 200 people have a rib that's coming off of this C7 vertebra up in the cervical area called a cervical rib.

07:49 Usually it's bilateral meaning there's one on both sides.

07:52 But it can be unilateral, meaning just one on one side.

07:57 Most of the time, there's no problems people are asymptomatic, but it can cause compression of structures and cause something called Thoracic Outlet Syndrome.

08:08 And that's because there's a lot of important structures that pass through this area, including the brachial plexus.

08:15 So compression of the brachial plexus can end up causing pain or numbness down in the forearm or hand.

08:22 And there's the subclavian artery and vein in this area too.

08:26 So you can compress those vessels.

08:28 And that gets even worse if the arm is abducted, worsening that compression.

08:34 And in the case of compressing the subclavian vein that can limit how much blood can return back to the body causing the upper limb to swell up.

08:42 But again most of the time, cervical ribs cause no problem at all.