Doctor of Physical Therapy, Gabe Dubberke

If you ask almost any physical therapist what areas of the body they treat the most, they would likely tell you knees, backs, and shoulders. Many of the most common shoulder injuries, such as impingement syndrome and rotator cuff tears, involve the rotator cuff either directly or indirectly, but, what is the rotator cuff exactly? 

The rotator cuff is a group of 4 muscles that start on your shoulder blade and end on your upper arm. Like all muscles, these contract and pull to produce force where they are attached. However, unlike your bicep which for the most part works to make your elbow bend or to raise your arm, your rotator cuff’s primary function is to provide stability not necessarily motion. 

To better understand the function of your rotator cuff it helps to know a little more about the shoulder joint itself. Your shoulder is one of the most mobile joints in your body. This is great, because it means you can use your arms to throw a ball, swim, play tennis, or put dishes away in the top cupboard. However, that amount of mobility comes with a drawback; Your shoulder has to be less stable in order to allow for all that motion.

Think of the way your elbow and knee each only really bend and straighten. These joints tend to be much more stable compared to your shoulder, which can move around in a big circle. The joint itself consists of the head of your humerus bone (the ball part of your upper arm bone) contacting your glenoid fossa on your shoulder blade (the socket part of the ball and socket in this joint).

Imagine the joint kind of like a volleyball resting on a dinner plate. To get good motion, the ball (the head of the humerus) needs to roll and glide on the plate (glenoid fossa). The trick is that we have to keep the ball stable in the center of the plate as it rolls. It can’t roll up onto the lip of the plate, otherwise we tend to experience problems and pain. That is where your rotator cuff comes in. Your rotator cuff muscles and their tendons extend from your shoulder blade out to your humerus. When these muscles contract they pull the head of the humerus into more firm contact with your shoulder blade and keep the ball in the center of the plate. In essence, they should be strong enough to provide stability to the shoulder but not so tight that they limit motion. 

The four muscles of your rotator cuff are the supraspinatus, infraspinatus, teres minor, and the subscapularis. Each of them are important and can be involved in a number of different injuries, but one of them tends to be more problematic than the others. If you have had a rotator cuff tear, the odds are that it was in your supraspinatus. This has to do with the location of the muscle and its tendon. As it runs out to the humerus, it runs underneath a bony hook that extends from your shoulder blade. That bony hook is called the acromion, and the space beneath it is called the subacromial space.

If your rotator cuff is not working properly, if your shoulder moves in a less than optimal way, or if that bony hook grows down, it can rub on the tendon of your supraspinatus and cause those tears. It is important to note that in most cases this needs to happen frequently over a long period of time to cause significant problems.

Rotator cuff tears aren’t the only problem that can occur in the subacromial space. Some people develop inflammation in that area which could be tendonitis or bursitis. Other people develop shoulder impingement, which is just a convenient name for pain that results from lack of room in the subacromial space. You may or may not be familiar with some or all of these terms, but as a physical therapist, I can tell you that all of them are very common and treatable in one way or another.

In many cases, one of the important aspects to consider in treating shoulder pain is the quality of the rotator cuff both in terms of strength and overall health. Fortunately, these injuries being common mean that many PTs are experts and very comfortable addressing the rotator cuff. If you want to learn more about the rotator cuff or if you have shoulder pain you want to get looked at, please get in touch with any of our therapists at 21st Century Rehab. We have physical therapists at each location that are experts in shoulder pain and rotator cuff injuries. You can view a list of our locations here or feel free to give us a call at 515-382-3366!