What are the Rotator Cuff Muscles?

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.

Shoulder Impingement

Impingement generally refers to structures becoming compressed in the tiny space they have to travel through, which can lead to pain and avoidance of using that muscle. While this sounds pretty straight forward, impingement can actually be pretty tricky to figure out, and requires thorough examination. This is because impingement can occur on its own due to structural problems or inflammation, but it can also occur because an original injury caused certain structures to subsequently become impinged. For example, the supraspinatous tear we described above can lead to impingement, so it's important to identify the underlying cause.

Impingement can often be identified based on what the patient reports, where exactly they feel their symptoms (see video on the painful arc test below), and with the use of some special hands-on tests, the doctor or physiotherapist can pinpoint the exact problem. For example, impingement may be primary or secondary, occurring either closer to the front or back of the shoulder. Treatment will depend highly on the cause of impingement and symptoms reported by the patient.

The following video describes what is arguably the most common test for shoulder impingement. Please keep in mind that one single positive test is never enough to confidently diagnose a particular injury, but rather, is used in combination with other tests and patient history in order to narrow the focus to the most likely condition. Nevertheless, the tutorial below provides a great description of what to expect, and there are many more videos by these guys for other conditions and exercises on Youtube.

Shoulder Instability

In order to save pages and pages of text, I lumped many conditions into the overarching category of instability, but nevertheless, it always involves the rotator cuff muscles somehow. For example, someone who dislocated their shoulder playing a sport will have a really loose shoulder joint, particularly in certain directions depending on the dislocation.  They may briefly be in a sling or shoulder brace after relocation, but it is important to get started with strengthening these muscles as soon as the body is ready to do so. 

In order to make the shoulder joint more stable and attempt to prevent future injuries, the rotator cuff muscles can be strengthened to provide additional support to the joint, making it an overall stronger structure. Remember, the rotator cuff muscles can all act together to pull the arm into the shoulder socket. Therefore, even if the joint capsule and ligaments become more loose, strengthening the rotator cuff muscles is a great way to make up for it. Moreover, physiotherapists are well-versed in designing exercises specific to the functional demands of the patient, which can make the treatment that much more effective.

Rotator Cuff Muscle Exercises

We won't spend too much time describing exercises, as you can find a ton of videos about rotator cuff exercises online. However, more importantly, everyone's injury will be unique, and therefore, their respective treatment plans will vary widely. That said, the following videos should give you a good idea of how to strengthen rotator cuff muscles in general, as well as what some of the more common exercises for treatment will look like.

The first video you will see below describes a few common exercises using a Thera-band, which is an extremely common piece of equipment in rehabilitation settings. These bands may seem a little simple, but there's so much you can do with them, either for rehabilitation or just strengthening your muscles in general.

The second video shows similar exercises; however in this case they use multiple positions, allowing you to see how you can adjust your exercises depending on your functional needs. It is also a good demonstration to show how the same 4 muscles can be used in many different positions, which really speaks to their importance in our daily function.


Conclusion

Overall, while this is all fairly general information, we hope you can appreciate the importance of the rotator cuff muscles, and why they are such a common source of treatment and injury. If you suspect you have a problem with your shoulder, we highly encourage you to get it check out by a healthcare professional, such as a doctor or physiotherapist, in order to have a personalized examination. This should get you on the road to feeling better, and even after one or two appointments, you will be able to take home some new knowledge and exercises to help you progress through your recovery and take control of the situation. All the best!

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