 This vignette, which in correlation with other vignettes, has been focusing on the six components of the cuff supraspinatus, infraspinatus, teresminus, subscapularis, caracohumraligaminincapsule is now going to address the arches about the shoulder. Arches, you say? Well, quite well you may. I'll explain them now. There are three of them. Let's begin with the one everybody knows, the medial arch. The arch below the AC joint. First, everybody has an abnormal AC joint. So you have to decide when you want to put the hammer down on the joint and the answer should be not very often. But as far as impingement goes, impingement is a clinical syndrome of inflammation and cuff disease and labral disease. So if you have encroachment on the medial aspect of the arch, call it just that. Stenosis or encroachment, but don't use the word impingement. Because the myotendinous unit is so strong and so powerful, it almost never gets interrupted at this medial arch. It may get compressed a little bit, but it's usually asymptomatic. The most important arch is the subacromial arch underneath the acromion, where the acromion may appear like a shelf or a keel or a telephone receiver and contributes to impingement syndrome anatomically. And then we have the third arch, the forgotten arch, the coracoid arch, that contributes to coracoid abutment syndrome and a condition known as antero superior impingement syndrome, also known as ASI. There is a coracoid index. There's a distance that some have proposed between the coracoid and the humeral head. None of those things work very well. I'm not a measure. I almost never measure. What do I do? I look at the degree of compression or encroachment of the tissues underneath it. Are they inflamed? Are they damaged? And are there secondary signs that there is abutment between the coracoid and the humeral head, like small, irritative, pseudosis and pitting, which there is? You might say, well, there's a pretty good distance here. You're right. But what about when they're lying down? What about when they're throwing? What about when their arm is cocked? There's probably abutment at some chain in that chain of events. And the same thing is true for the other types of pseudosists and derosions that you see in the humeral head. Or in the back of the shoulder, there's usually contact with the acromion with the arm cocked. If they're in the front of the shoulder, there's usually contact with the acromion with the arm in front of the mid-coronal plane, the three arches. The medial arch at the level of the ac joint, contributing sometimes to stenosis, but rarely contributing to actual inflammatory impingement or cuff tears, the lateral arch, the major contributor, and the off-forgotten subcoracoid arch, deep to the coracoid in front of the humeral head.