 Okay, we're talking about the six key components of the rotator cuff complex, the supraspinatus, the infraspinatus, the teres minor, the subscapularis, the capsule, and the coraco-humor ligament. We've shown you in other vignettes injuries of all of them and how to assess them in different projections. But I want to focus just for a moment on the surrounding anatomy. Firstly I want to focus on the subacromial arch. This case of a massive rotator cuff tear, there is no supraspinatus. There is massive retraction with the fibers seen medially, was instigated at least in part by this funny looking acromion. The acromion has been a subject of much debate and much discussion. There's even a catarization of the acromion called the bigliani subtypes of the acromion. I hardly ever use that. What I do use is the proper descriptors. I like to see if the acromion is downsloping in the coronal projection. There is a sloping angle, but that's a little bit beyond the discussion today. How often do I use it? Never. I rarely measure things, but I do look at them. So downsloping in the coronal projection is a little different than downsloping in the sagittal projection, but I pay attention to both. Then there is the shape of the acromion. Very often people that have anatomic impingement have an acromion that has a little shelf on it that looks a little bit like the end of a telephone receiver. You'll also hear this called a keel-like acromion. I often refer to it as a telephone receiver acromion. Now when you're younger, the acromion plays a scant role in impingement unless you have a humeral head that won't stay down. In other words, it starts floating up when you pick your arm up. In other words, there's micro instability. The humeral head doesn't rotate in the center of the cup. If you pick your arm up and the humeral head goes up, what does it bump into? The acromion. As you get a little bit older, the acromion remodels, and it becomes like this, keel-like. And now you've got a self-perpetuating prophecy. The humeral head is up, the acromion's in the way, the acromion further damages the rotator cuff, the humeral head comes up higher, and eventually, and unfortunately, they meet, bone to bone. There is another structure that participates in this process, and that is the caracochromial ligament. The caracochromial ligament comes off the acromion and heads towards the coracoid. Now this patient's caracochromial ligament is not that well seen, it's right here, and it's not that thick. It's a little bit thick, but most of the time, if you went to decide whether the ligament or the bone is a bigger contributor to anatomic encroachment, it's more often the ligament than the bone. It's about 60, 40, 70, 30. But either one can do it, and sometimes it is both. In this case, it's more bony than it is ligamentous. Let's take a quick look at the sagittal projection for a moment and see what our acromion looks like in the sagittal projection. When we say that the acromion is downsloping, here's what we mean. Here's our humeral head, not a very good drawing of it, and if our acromion is tilted down from postural craniad to anterocautad, it's positively downsloping. If it's straight in line with the humeral head, something like this, then it's neutral, and if it's angled up, then it's negative slope. We don't pay too much attention to that. We are more interested in positive sloping, but especially whether the acromion has a hook or a spur associated with it. It often looks quite different in the sagittal projection. It often looks like it has a little snout, and that snout is where the caracochromia ligament attaches. So you have a fat acromion that has a snout or a spur, and if it's downsloping sagittally, which this one really is not, and in the coronal projection, you have a keolike or telephone receiver acromion, which in this case it is, and if you have a thick caracochromia ligament, which in this case it's a little bit thickened, but not very much, all of those components are part of the analysis of impingement syndrome and contributors to rotator cuff pathology.