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  • Tara Albright DPT

Meet Your Rotator Cuff: Rotator cuff anatomy and function

You wake up feeling very stiff and sore, but what’s new? You go to reach overhead and stretch, and feel this nagging pain in your shoulder as you reach overhead. You don’t think too much of it because you did a lot of yard work yesterday. As time goes on, the pain seems to get worse with putting dishes away into the overhead cupboards, reaching for your seatbelt in the car, sleeping on your side and you start to wonder, “is there something wrong with my rotary cup?” How many people have gone through this scenario or something similar and wondered “what is exactly going on?” In this blog we attempt to explain some background on what the ROTATOR CUFF is and why when it stops working it can lead to pain?

Let’s start off with a common misconception, which is the fact that the rotator cuff is not just one muscle, but is actually made up of 4 muscles that work together to allow your shoulder to “rotate”, hence the name rotator cuff, to allow you to reach overhead as well as behind your back. The 4 muscles are the supraspinatus, infraspinatus, Teres Minor, and subscapularis. Each of these muscles has a specific position, which allows them to perform a specific task of moving the arm, to allow the shoulder to function in a multi-plane aspect. This means that when we raise our arm to reach into the cupboard our arm can be straight in front of us, or off to the side, or even behind us and still function appropriately.

The supraspinatus is often the most impacted muscle when everything does not go as planned. The supraspinatus’ main function is assist in guiding the bone to rotate in the joint when the arm is being raised out to the side or into an overhead, in front of you motion. Here is a quick GIF to help you understand its function.

You can imagine, with the location of the supraspinatus tendon, that if it does not function correctly, the top of the arm bone (humeral head) will collide with the underside of the top of the shoulder girdle (known as the acromion process) and will inadvertently pinch the rotator cuff muscle, leading to inflammation and pain.

The second most important rotator cuff muscle is the infraspinatus, which is the main lateral rotator in the shoulder. This muscle assists people in rotating their arm to reach their seatbelt, reach out the window in a drive-thru, or reaching back when putting a coat on. This is also a very helpful muscle in many sports like swimming, tennis, and baseball. This muscle attaches just under the bursa and can be greatly affected when the shoulder joint is inflamed. Click the video above to see how the infraspinatus functions.

The third muscle of the rotator cuff is the Teres Minor, which is the main muscle that stabilizes the humeral head (top end of the upper arm bone) in the glenoid cavity of the scapula (socket portion of joint on the shoulder blade). This muscle also assist the infraspinatus muscle in laterally rotating the shoulder as well as extending the arm (i.e. reaching behind you) although it’s main function is to stabilize the shoulder joint.

The fourth muscle of the rotator cuff is the subscapularis muscle. Its main function is also the stabilization of the joint, however this muscle furthermore assists in a vast amount of daily activities including opening a tightly sealed jar, reaching back to scratch your back, clutching a book to your chest, and even giving a hug. This muscle is also useful in throwing a fast ball and performing the overhead swimming stroke.

As you can tell, these 4 muscles need to work as a unit to maintain full functional use of the shoulder joint in various daily activities and sports. Although these muscles are key to assisting the shoulder joint in its function, there is another important piece of the puzzle, which is known as the labrum. This is a thick band of tissue that surrounds the glenoid, or shoulder joint, to assist in deepening the joint and providing improved stability. The shoulder joint is a very shallow joint and without this band of tissue the shoulder would not be able to move in the various ways that we need it to meet our daily needs.

I think it is safe to say, the shoulder joint is a very complex joint, which is needed to move in all planes of motion in order to meet or daily needs. If one or more of these components are not functioning up to par, it can create a major issue, leading to increased pain and decreased function of the arm as a whole. Physical therapy can assist with many types of shoulder pain and address the underlying weakness, tendonitis, or instability that is creating the impairments and pain. Our goal is to get you back to your normal life as soon as possible.

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