Rotator Cuff Muscles And Shoulder Pain – Why Does It Happen?
Shoulder pain is a relatable experience for many people. And, one of the most common sources of that pain is dysfunction or injury of the rotator cuff muscles. In this article, we’ll take a look at why that muscle group is so often associated with shoulder pain.
What and where are the rotator cuff muscles?
Before we dive into shoulder pain, let’s take a moment to review this muscle group. Remember that we have four rotator cuff muscles: subscapularis, infraspinatus, teres minor, and supraspinatus. All four of these muscles attach to the scapula at one end and the humeral head on the other end. The tendons of these muscles all come together and form a cuff around the humeral head which is where the group gets its name.
What are the actions of each of the rotator cuff muscles?
Each of the rotator cuff muscles has a specific primary action. Remember that the subscapularis does medial rotation of the humerus. The supraspinatus initiates abduction of the humerus. And, infraspinatus and teres minor do lateral rotation of the humerus.
However, although every anatomy book lists specific actions that these muscles do when they concentrically contract, one of their most important actions is actually stabilization. They work together as a group to stabilize the humeral head in the glenoid fossa from multiple directions. For example, subscapularis helps stabilize the humeral head and resists anterior translation. Infraspinatus and teres minor balance that. They stabilize the humeral head and resist posterior translation.
With that in mind, we could consider that a primary “job” of the rotator cuff muscles is to stabilize the humeral head in the socket so that we can use our arms and hands to do fine motor movements. Each of the four muscles on its own is a relatively small muscle. They act as synergists alongside more powerful prime movers rather than initiating big movements themselves.
Why are healthy rotator cuff muscles so important?
The socket (called the glenoid fossa) where the head of the humerus inserts to form the shoulder joint, is shallow. It takes muscles, ligaments, and tendons all under the right balance of tension to hold the head of the humerus in the socket and keep the joint functional. Any injury or strain in one muscle of the rotator cuff will affect the stability and balance of the whole shoulder joint.
Why are the rotator cuff muscles so often a cause of shoulder pain?
Many sources note that rotator cuff tendonitis is the most common cause of shoulder pain. But why is that? There are a few reasons. One simple reason is overuse. We do a lot of activities at work, at home, and for leisure that use our shoulders in repetitive ways. Remember that the whole shoulder complex, including the shoulder joint specifically, is very mobile. This allows us to do all kinds of things including specific fine movements with our hands and arms. But, it also makes it easy to overdo it when we use these muscles. Repetitive use can lead to inflammation, irritation, or injury of these muscles.
Repetitive motions from work activities or sports can also cause an imbalance in the tension held between the different rotator cuff muscles. And, another very common cause of shoulder pain is an imbalance of tension between the those muscles. That can put strain on the shoulder joint and result in pinched nerves, pressure on a bursa, or just generally irritated connective tissue.
Muscles don’t work in isolation, so an imbalance between other agonist and antagonist muscles can also result in an imbalance in the tension of the rotator cuff muscles. Additionally, the position of the shoulder is related to the position and tension of structures in the larger kinetic chain. So, the location of the torso, ribcage, spine, etc. also influences the position of the shoulder joint, and indirectly they influence the tension in the rotator cuff muscles.
Using a small muscle for a big job
Using the rotator cuff muscles for actions they’re not well-suited for can also result in shoulder pain and injury. The classic case is suddenly lifting a heavy suitcase and tearing supraspinatus. In fact, supraspinatus is the most common muscle of the rotator cuff group to get injured. It’s sometimes even referred to as the “suitcase muscle.” This is because of its association with getting irritated when we suddenly pick up a heavy suitcase and ask this muscle to do more work than it’s cut out for. However, any and all of the four rotator cuff muscles and their associated tendons can get injured if we use these muscles for big actions that they’re not well-placed or sufficiently large to handle.
Acute trauma to either soft tissue or the bones of the shoulder can of course also cause injury to one or more of the rotator cuff muscles and cause shoulder pain. And age-related wear and tear of this muscle group can contribute to shoulder pain as well. Finally, the genetics that inform how everything comes together at your shoulder joint can affect the likelihood of experiencing rotator cuff-related shoulder pain. For instance, you may have less space below the acromion potentially creating a higher likelihood of compression, bursitis, fraying of the supraspinatus tendon, and even bone spurs.
Types of rotator cuff-related shoulder injury and dysfunction
Depending on the location and cause of the rotator cuff issue, there are different types of injuries and dysfunction that can result. The specific diagnosis of each of these dysfunctions should be handled by a medical professional and is far beyond the scope of this article.
Generally, issues with these muscles could include:
- Rotator cuff tendonitis
- Partial thickness tear
- Full thickness tear
- Subacromial impingement syndrome
- External impingement syndrome
Symptoms of rotator cuff-related pain
Rotator cuff-related shoulder pain might show up as:
- General shoulder aches and pain
- Pain when doing repetitive tasks with the shoulders
- Shoulder pain while lying on the shoulder when sleeping
- Shoulder muscle weakness or weakness when moving the shoulder
- Additionally, there are many orthopedic tests for specific rotator cuff muscle dysfunction that are beyond the scope of this article
Treatments for rotator cuff-related shoulder pain
Treatments depend on each specific situation. If you have shoulder pain or suspect rotator cuff issues, you should consult with an appropriate medical professional for an assessment. Initial treatments for mild tendonitis might involve taking a break from activities that overuse your shoulders in a particular way. Ice and rest can often help reduce inflammation. If the issue is caused by a muscular imbalance, then an experienced physical therapist or bodyworker may be able to help. Appropriate stretching and strengthening exercises are often suggested to address the underlying causes behind mild tendonitis or small tears. In the case of more significant tears or acute trauma to the rotator cuff, surgery might be necessary.
There are many reasons why we might strain or injure a rotator cuff muscle. That makes this area one of the most common sources of shoulder pain. The balance of tension between these four muscles is important for maintaining a full range of motion of the shoulder. If one rotator cuff muscle is injured, it affects the kinematics of the whole shoulder. So there are also lots of good reasons for giving this area some extra care in order to maintain a healthy rotator cuff.
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Rathi, S., N.F. Taylor, B. Soo., and R.A. Green. 2018. Glenohumeral joint translation and muscle activity in patients with symptomatic rotator cuff pathology: An ultrasonographic and electromyographic study with age-matched controls. Journal of Science and Medicine in Sport. 21:885-889.
Varacallo M., Y. El Bitar, S.D. Mair. 2023. Rotator Cuff Tendonitis. [Updated 2023 Aug 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532270/