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Article

The rotator cuff: what is it?

The rotator cuff is a term you have probably heard in connection with the shoulder, for example in relation to shoulder injuries or warming up before strength training. Many people, however, do not know what the rotator cuff actually is and what function it has in the shoulder. In this article we therefore look more closely at this topic.

The rotator cuff

Anatomy of the rotator cuff

The shoulder joint consists of two bones, the shoulder blade (scapula) and the upper arm bone (humerus). Together they form a joint in which the socket of the shoulder blade receives the ball of the upper arm bone. The socket is very shallow compared with, for example, the socket of the hip joint. The joint is therefore fairly poor to begin with. Around the socket we have a labrum, which makes the socket somewhat deeper, and we also have a joint capsule and ligaments that provide further stability. However, this is not enough and we depend on muscles to increase the stability of the joint. This is where the rotator cuff comes into the picture.

The rotator cuff is a muscle group consisting of the four muscles supraspinatus, infraspinatus, teres minor and subscapularis. They all arise from different parts of the shoulder blade and attach high on the upper arm bone near the joint with the shoulder blade. The first three muscles come from the back of the shoulder blade, that is, on the back side, while the last muscle, subscapularis, arises from the front of the shoulder blade. What is somewhat special about the rotator cuff is that the tendons of the different muscles all weave together and form a broad sheet of tendon tissue that covers large parts of the shoulder joint. This is slightly different from typical tendons, which are often easier to tell apart. Think of the tendons you can easily see in the forearm…

The function of the rotator cuff

Now that we know a little more about the anatomy, we will look more closely at the function these muscles have in the shoulder joint. We will take the muscles that come from the back of the shoulder blade first. Teres minor and infraspinatus are positioned so that, in isolation, they can rotate the upper arm outwards. They can therefore contribute to external rotation in the shoulder joint. Supraspinatus is positioned so that it can lift the arm out to the side, but it is speculated whether it can contribute to external rotation and perhaps also internal rotation depending on the position of the upper arm. Subscapularis, which lies on the other side of the shoulder blade, is positioned so that it can rotate the upper arm bone inwards and thus contribute to internal rotation in the shoulder joint. These are the isolated functions that many people tend to think of when it comes to the rotator cuff. But the rotator cuff has another and much more important function in the shoulder. These muscles work together to provide stability in the shoulder joint by making sure that the ball of the upper arm bone stays centred in the socket. Put simply, the rotator cuff makes it possible for us to use other muscles to move the arm, especially with great force.

Connection with shoulder problems

When it comes to shoulder problems, the rotator cuff has often been seen as the culprit, and because of its important function it is easy to catastrophise if you find out that you have damage to the tendon tissue. What is important to be aware of, however, is that such findings are very common also among people who do not have shoulder problems, which suggests that such changes alone are not enough to explain any pain or problems. In many cases you can cope perfectly well even with larger ruptures in the tendon tissue.

The extent of tendon changes and ruptures is often picked up on imaging such as MRI scans, but did you know that extensive changes and ruptures are also found in a large proportion of the population who do not have shoulder problems? The images do not mean everything.

We hope this was a useful introduction to the rotator cuff. Feel free to read our article on rotator cuff-related shoulder pain.

References:

  • Ihashi K, Matsushita N, Yagi R, Handa Y. Rotational action of the supraspinatus muscle on the shoulder joint. J Electromyogr Kinesiol. 1998 Oct;8(5):337-46. doi: 10.1016/s1050-6411(97)00038-2. PMID: 9785254.
  • Jeno SH, Munjal A, Schindler GS. Anatomy, Shoulder and Upper Limb, Arm Supraspinatus Muscle. [Updated 2023 Aug 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537202/
  • Maruvada S, Madrazo-Ibarra A, Varacallo M. Anatomy, Rotator Cuff. [Updated 2023 Mar 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441844/
  • Cooper JD, Seiter MN, Ruzbarsky JJ, Poulton R, Dornan GJ, Fitzcharles EK, Ho CP, Hackett TR. Shoulder Pathology on Magnetic Resonance Imaging in Asymptomatic Elite-Level Rock Climbers. Orthop J Sports Med. 2022 Feb 11;10(2):23259671211073137. doi: 10.1177/23259671211073137. PMID: 35174249; PMCID: PMC8842184.