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What exactly does a rotator “cuff” do? And why is it such a common injury?

Well first of all, it’s not singular! It is in fact made up of 4 singular muscles. We see a lot of rotator cuff strains, tears, and surgical repairs in PT. But why? Anatomically the rotator cuff is made up of a series of four small, long muscles that reach around from the shoulder blade and hold the head of your upper arm bone in its socket. Picture a golf ball sitting on top of a T. Now picture those cheesy vending machines you find at Walmart or at arcades where you try to aim to pick up a stuffed animal, wrapped around that golf ball but going THROUGH a sock. That claw is your rotator cuff. Each arm represents a different muscle that helps hold that bone in place. The sock represents the tight protective capsule around both the golf ball and T. Now let’s talk about which muscle does what.

Supraspinatus. Supra, meaning “above.” Spinatus, referring meaning spine of the scapula. The name itself tells you where it is. It starts above a ridge on the back of the scapula, goes underneath your collarbone, and inserts into your upper arm bone. It helps with reaching up in front of you as well as out to the side. In fact, it’s the major initiator of the movement. The bigger muscle that cover it (the caps on the outside of the shoulder) only help once the supraspinatus moves the arm the first 15 degrees. Because it goes under the collar bone, it is prone to getting pinched if you move wrong, causing irritation and fraying. On the other hand, if those muscles aren’t very strong, the bone can slip partially out of socket, putting you at increased risk of dislocations.

Infraspinatus. Infra, meaning “below.” Spinatus, coming from the spine of the scapula. What a copycat huh? This guy does the same thing, except he’s below the last muscle. He however, does not go underneath the collarbone, but rather attaches slightly behind the tip of your shoulder. His job is to help with external rotation of the shoulder and also help stabilize in the back of the joint and helps support the capsule.

Teres Major. Teres meaning “rounded” and major designating it as larger than minor. He is also known as the “little Lat” as he assists the Latissimus Dorsi with rotating the arm inward and bringing it closer to your side. This guy sits below infraspinatus, coming from the lower part of the scapula and inserting below infraspinatus on the arm bone.

Subscapularis. Sub meaning, “under” and scapularis meaning “spade” referring to the shoulder blade. This guy you cannot see because he sandwiched between the ribs and scapula and inserts in the front of the arm bone. His job is to help with internal rotation and adding the arm to the side, as well as moving the arm bone forward and down when raising the arm, keeping the supraspinatus from getting pinched.

Because the shoulder allows so much movement due to the shallow socket, these muscles can become “strained” if they are stretched more than allowed, and can even tear completely during a traumatic injury such as trying to catch something heavy from falling. However, day to day use can also cause injuries. Bad posture alone can cause problems due to changes in the joint pinching the rotator cuff muscles from slouching forward, causing tendonitis. If you work at a job where you have to do repetitive movements in addition to poor posture you are even more at risk. A classic example would be someone who does a lot of overhead work such as painting. It’s also worth noting that the shoulder joint is also very closely related to the scapula itself, which has 17 different muscles (including the rotator cuff) helping it work properly. If these muscles surrounding the shoulder blade are weak it compromises good quality movement in the shoulder joint. This is why we also spend a lot of time strengthening these muscle in the upper back. You cannot strengthen the shoulder unless the foundation (aka the shoulder blade) has a stable foundation on which to move. We hope this blog post helps you understand how the rotator cuff works as well as the structures involved. If you ever find yourself suffering from a rotator cuff injury/tendonitis or are concerned that you may need surgery contact us. We’d be happy to help!