 Time for the shoulder joint. Now, elbow joint, not very mobile, very stable. Shoulder joint, holy mobility. In fact, it's the most mobile joint in your body. What does that tell you about its stability? It's not a very stable joint. And in fact, dislocations of the shoulder, rotator cuff injuries, I mean, the shoulder is often a damaged joint. Two bones involved, the humerus, the head of the humerus articulates with the glenoid cavity on the scapula. And because really there's so much movement possible, if you put a whole bunch of stuff around it, it would make the movement more difficult. So there are some unique structures that are in place to help stabilize this joint. First of all, there is a fibrocartilage lip that's on the outside of the glenoid cavity of the scapula. And that is located right, I've got to have my pen. It's located right here. And this thing is called the glenoid labrum. Labrum, and it's made of fibrocartilage. Normally, our articulating bones are lined with articular cartilage, which is made out of what? Hyaline cartilage, and you can see that here. We still have the hyaline cartilage, articular cartilage, but we also have an added structure, the glenoid labrum. It just kind of increases the reach of the glenoid cavity and helps hold that humerus in place just a little bit. You can see my articular capsule right here. There are many, many ligaments that are involved, look at them all, that are involved in helping to hold the humerus in place. We actually aren't going to learn the ligaments. What we are going to look at are the muscles that are involved in stabilizing that joint. One of them we can see right here. You can't actually see the muscle. Okay, I'll just draw it in for you because you know. There it goes. And this is an anterior view. This is actually biceps brachii, biceps brachii, and biceps brachii by 2 has two heads. There is a tendon. The tendon of the long head of biceps brachii actually runs up and over the humerus through the inner tubercular groove between my two greater and lesser tubercles. And that long head of the biceps actually attaches to the superior aspect of the glenoid bossa. And can you imagine how if that tendon is running across up through that groove and then attaching to the superior part of the glenoid bossa, it's going to hold the head of the humerus in place. Can you visualize that? Of course you can because I'm such an excellent describer of things. That's why we have to know this bad boy today and not in muscle land. More muscles that we have to know today. We're going to know all the rotator cuff muscles. Why? Because the rotator cuff muscles, all of them attach to the scapula and attach to the greater and lesser tubercles of the humerus. Now think about that. Here's a muscle that spans from the scapula to the humerus. And if it shortens, they like hug the head of the humerus. And while they're hugging the head of the humerus, if they shorten, they actually squeeze the humerus back into the glenoid cavity because they're shortening and pulling it in. Essentially stabilizing the joint, keeping the head of the humerus in the glenoid cavity. Okay, can you visualize it? You know you can. So let's take a look at them. There's four of them. Look at this. This is, look, I'm showing you his face. This is the anterior aspect of somebody's scapula in life. Really? Now think about this for a second. That means that we've taken out his rib cage, we've taken out all of his guts, we've taken out the back of the rib cage, and all we're looking at is straight on through all that emptiness now at the scapula. And what surface is that? You know this. What surface of the scapula am I seeing? The subscapular fossa. Guess what muscle attaches to the subscapular fossa? What rotator cuff muscle attaches to the subscapular fossa? Really? Sub-scapularis. How easy is that? Not only is subscapularis the only rotator cuff muscle that attaches on the, you have to call it the anterior side of the scapula. It's the only one that attaches to the lesser tubercle. All my other rotator cuff muscles attach to the greater tubercle. Okay? So subscapularis attaches to the lesser tubercle of the humerus. And look it, it's hugging the humerus. Easy. Now, you are now looking at the backside. Okay, look, I'm going to put some hair on this person. And now, you're looking at my person. But guess what? You're looking at the back of his head. All right? So now we're looking at the backside. Just take off the skin, no problem. Now we should be able to see all these muscles. It's not crazy. They all attach to the greater tubercle. This friendly friend attaches to the supraspinus fossa. And it's supraspinatus. What? Don't you love that? That's why we're doing it now, because it actually is pretty straightforward. Who is attaching to the infraspinus process? Infraspinatus. And who is attaching to the lateral, upper lateral border of the scapula? Could it get any easier than this? It's Tyri's minor. Okay, that one makes absolutely no sense. The other two, done. You already know your scapula marks. Tyri's minor, okay. You're going to have to memorize one muscle here. But you have to know it next week anyway, so you might as well learn it now. Tyri's minor is the most inferior of the group, like it's on the bottom of the line, but all of them are attaching to the greater tubercle. And hugging my little buddy, the head of the humerus. Okay? Let's do the knee. It will be really fun.