What Are The Rotator Cuff Muscles?
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Quick NavigationRotator Cuff Muscles – SITSWhat do they do?Common Rotator Cuff InjuriesSupraspinatous TearsShoulder ImpingementShoulder InstabilityRotator Cuff Muscle ExercisesConclusion
The term “rotator cuff” is used a lot in the context of sports and shoulder injuries. The reason for this is the prevalence of which the rotator cuff is involved in shoulder injuries. It is a common site of irritation, acute trauma, and overuse/chronic conditions. In fact, it’s actually quite difficult to sustain a shoulder injury without any involvement of the rotator cuff at all, and this is the reason we would like to explain the rotator cuff muscles in a little more detail.
Therefore, in this article, we will touch on the individual rotator cuff muscles, their actions, how they function together, and a little bit about rotator cuff injuries, diagnosis, and treatment for the rotator cuff muscles. That said, please keep in mind that in order to receive a diagnosis or treatment that will work for your specific condition, it is best to visit a doctor or a physiotherapist for one-on-one consultation.
Rotator Cuff Muscles – SITS
Technically, the rotator cuff is comprised of 4 separate muscles, each with their own distinct origin, insertion, and action. While other muscles not listed here will help assist the rotator cuff muscles in performing their actions, these four muscles are considered to be the true rotator cuff muscles. When I was learning the anatomy of these muscles, I found it easiest to remember them with the acronym SITS. This is a very popular acronym to use when learning the rotator cuff muscles, so you may occasionally hear them referred to as “the SITS muscles” as well. S = Supraspinatous I = Infraspinatous T = Teres minor S = Subscapularis|
Muscle |
Origin/Insertion |
Action |
Innervation |
|---|---|---|---|
| Supraspinatous | Surpaspinous fossa/greater tubercle of humerus | Shoulder abduction | Suprascapular nerve |
| Infraspinatous | Infraspinous fossa/posterior aspect of greater tubercle of humerus | Shoulder external rotation | Suprascapular nerve |
| Teres Minor | Infraspinous fossa/posterior aspect of greater tubercle of humerus | Shoulder external rotation | Axillary nerve |
| Subscapularis | Subscapular fossa/lesser tubercle of humerus | Shoulder internal rotation | Subscapular nerves |
What do they do?
The shoulder is the most mobile joint in the body; however, this comes at the cost of stability. It’s easy to picture the shoulder as a ball-and-socket joint like the femur in the pelvis, where the head of the femur is well inside the socket, but the shoulder is actually a lot less congruent. In fact, only about 1/3 of the head of the humerus is ever in contact with its socket (the glenoid) at any one time. This means the shoulder requires a lot of extra help to stay stable and functional. The joint capsule itself helps to hold the shoulder in place with numerous ligaments, but otherwise, most of the stability comes from the rotator muscles as they cross over from the scapula to the humerus. They almost form a shell around the shoulder joint, and when they contract uniformly, this pulls the humerus tighter into its socket. These muscles aren’t only important for keeping the shoulder in at rest, but they also allow our arms in general to work in a functional manner. They anchor the arm into the upper body, allowing other muscles to work while they keep everything in place. They are involved with every type of shoulder movement, so given how often they are used, they become more prone to both acute and chronic injuries.Common Rotator Cuff Injuries
Almost all injuries to the shoulder will involve, or at least affect, the rotator cuff to some degree. Therefore, with any shoulder injury, one should be suspicious of rotator cuff involvement, and the treatment may target those muscles to some degree as well. Nevertheless, here are some conditions that you may hear of more frequently.Supraspinatous Tears
The supraspinatous is a rotator cuff muscle that essentially crosses the top of the shoulder. The actual muscle belly can be found on the top portion of the back of your shoulder blade underneath the bulkier trap muscle that is active when shrugging your shoulders. The supraspinatous quickly thins out to form its tendon, which is much smaller than the muscle belly. This tendon then runs through what is known as the subacromial space, but for all intents and purposes, all you need to know is that it is a fairly confined space.
The tendon then travels over the top of the shoulder joint capsule and attaches on to the side of your upper arm (humerus). Given that it is really thin and attaches to the very top of your upper arm, it’s actually a really difficult muscle to find on yourself, but the trained hands of a doctor or physiotherapist will be able to identify it fairly quickly.
This tendon is often injured and is a common culprit in overuse injuries. For example, people who do have their arms constantly over their head, for example occupations that require a lot of overhead work, will sometimes experience irritation and inflammation of this tendon. If it becomes weak, partial tears can occur, but full tears are also possible, albeit generally more traumatic.
Since the supraspinatous muscle is responsible for shoulder abduction (bringing the entire arm off the side of your body out towards the side), this movement will definitely be compromised. Specifically, this muscle plays a large role in the eaerly stages of abduction, so just when you begin to lift your arm. At some point, the line of pull of the deltoid muscle (the big shoulder muscle you can feel on your upper arm) will be in a better direction for functional use, at which point it can essentially take over. Therefore, one of the telltale signs of a supraspinatous tear is hiking of the shoulder in order to initiate that abduction movement.