Rotator Cuff Anatomy and Disease

00:00 Here, we'll review a little bit about the rotator cuff itself. Now you may remember that the rotator cuff is composed of 4 specific muscles. On the back of the scapula above the spine of the scapula is the supraspinatus, underneath the spine of the scapula on the back of the scapula is the infraspinatus, and then deep to the scapula on the inside or front side of the scapula is your subscapularis. In addition, there's a muscle called the teres minor which is essentially grouped in with the infraspinatus muscle because it largely performs the same task. So when we're talking about shoulder movements, we're mostly focusing on those first 3. So the supraspinatus is responsible for abduction, lifting up your shoulder while the infraspinatus is responsible for external rotation, and the subscapularis is responsible for internal rotation. So since our patient is reporting pain and weakness with external rotation, it sounds like you probably has some disease involved with this infraspinatus which again is responsible for external rotation. But, is the disease of his rotator cuff a tear or is it just tendinopathy? We'll have to get some more information to sort that out. First off, a quick review. The progression of rotator cuff disease as shown here on the figure to my right, a person who initially just strains the muscle but you have just a few fibers of that muscle that have been torn with progressive problems with the shoulder. Maybe it's an overuse issue or repeated strain. A person can develop an uncomplicated tendinopathy. That may be associated with some nearby inflammation of the bursa so-called subacromial bursitis, and you may even have some evidence of impingement syndrome because that tight space between the acromion and the humeral head doesn't accommodate a lot of inflammation so if the bursa is inflamed it may limit your ability to flex your shoulder or abduct your shoulder as well. With time, however, and progressive use of that shoulder or progressive disease you can end up with a tear. So this shows tendinopathy complicated by, in this case, a supraspinatus tear. The confusing piece here is that our patient didn't just have pain and weakness, he also had this stiffness issue and a person who has a rotator cuff tear you still should be able to passively move their shoulder in all the different degrees of freedom we talked about. So, what is it that's causing this patient to be unable to move their shoulder even when we're moving it for them? Let's take a step back to review the typical findings for a patient with a rotator cuff tear and what doesn't quite make sense with our patient. So, this figure here shows something called the painful arc test. If somebody has a supraspinatus problem, you can lift up their arm passively and ask them to slowly lower the arm and let you know where they're experiencing pain as they go down and this slight highlights what the real role of the rotator cuff is. The rotator cuff is not really the mover and shaker and strong part of shoulder movement. That's really the job of the deltoid muscle or the latissimus dorsi muscles. Instead, the rotator cuff's job is to anchor the humeral head in the glenoid fossa of the acromion. So when you're starting to lower your shoulder down or lower your arm down, if your rotator cuff is unstable once you get to this point at about 120 degrees your rotator cuff starts to fail to do its job, there's instability and the patient would drop their arm or at the very least the patient would experience significant pain as they're locating or as they're lowering their arm. So, officially, the painful arc test is when a patient reports significant pain when they get to about 120 degrees and then down to around 60 degrees, after 60 degrees typically the rotator cuff is no longer necessary to stabilize the humeral head. If while a patient is lowering their arm, they have such instability and discomfort that they drop their arm, the drop arm test suggests not just tendinopathy but actually a rotator cuff tear. None of these issues though would explain the limited range of motion with passive and active testing. So let's tease out what would cause active and passive range of motion problems.