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A Guide to the Shoulder: The Rotator Cuff
The Shoulder Complex: Synergy in Motion
The Shoulder: Complex in Range and Structure
The shoulder is one of the most complex joints in our body. It offers the widest range of motion (ROM) and is capable of movement in all four anatomical planes: the frontal (sagittal), side to side (coronal), rotational (horizontal), and a combination of all three. This wide spectrum of range, however, comes with a cost: decreased stability. The shoulder due to its versatility, therefore, is more subject to injury and/or illness. The focus of this hub will be to explain in simple terms the complexity of shoulder anatomy with an emphasis on the shoulder's primary stabilizing structure: the rotator cuff.
The Shoulder: Synergy in Motion
The shoulder complex can be described as pure synergy in motion. The shoulder as a unit is comprised of four separate joints working together to produce an almost endless combination of shoulder movements. These four joints are:
- Glenohumeral Joint: Consists of the Scapula and Humerus
- Scapulothoracic Joint: Consists of the Scapula and Rib cage
- Sternoclavicular Joint: Consists of the Sternum and Clavicle
- Acromioclavicular (AC) Joint: Consists of the Scapula and Clavicle
For the purposes of this hub, the Glenohumeral (GH) joint will be discussed due to its dependency on the four rotator cuff muscles for overall stability.
The Glenohumeral Joint:
When people speak of the shoulder, more often than not is the glenohumeral joint they are referring to. This makes sense because the two primary bones that comprise the shoulder, the Humerus and the Scapula, come together here. The Glenoid Fossa, which gives the joint part of its anatomical name, is located on the scapula.
The Rotator Cuff Muscles:
Since the Glenoid fossa is a shallow depression on the scapula, the humerus is allowed a large range of motion. For a better mental picture of the GH joint, think of a golf ball sitting on a tee. The ball is the end of the humerus and the tee is the glenoid fossa. As you can see, there is a lot of range available. Contrarily, there is a lot of support needed to keep our hypothetical golf ball in place.
That support comes in the form of four muscles which together form the rotator cuff. These four muscles are commonly referred to as the SITS muscles. They are:
- S: Supraspinatus
- I: Infraspinatus
- T: Teres Minor
- S: Subscapularis
Each one of these muscles has at least one major function (action) in addition to working synergistically to stabilize the head of the humerus in the glenoid fossa. These four muscles are in essence, the wrapping (cuff) that keeps the rotation of the humerus in place. IOW: the rotator cuff.
The Rotator Cuff Muscles: What They Do
Each rotator cuff muscle as previously stated has its own action in addition to working as a group to stabilize the humerus. These individual actions are:
- Supraspinatus: Abduction of the shoulder. Or moving the arm up and down when placed at the side or in a diagonal plane.
- Infraspinatus: External rotation of the shoulder. Or, the action of placing your arm behind your back in order to scratch it.
- Teres Minor: External rotation of the shoulder; explained above.
- Subscapularis: Internal rotation of the shoulder. Or, the action of reaching across your body to grab something.
Each of these actions takes place individually and in concert with each other. In short, rotator cuff muscles are synergistic. I sense a theme...
An Ounce of Prevention...
Due to its inherently fragile nature, the rotator cuff is one of the most commonly injured structures in the body. Just think of all the motions your shoulder goes through on a daily basis and you begin to understand how important these small, yet integrally-related, muscles are. Although their strength is not that dramatic compared to larger muscle groups, the 4 rotator cuff muscles are strong beyond their size. And, as with other muscles, stretching and strengthening your rotator cuff muscles is a great way to prevent future or further injury.
Two quick notes:
- When stretching a muscle, you position it OPPOSITE its primary action. For example, to stretch the shoulder's primary internal rotator, the subscapularis, you stretch the shoulder into external rotation.
- When strengthening a muscle, you add resistance to its primary action. For example, to strengthen the supraspinatus, you'll add resistance to shoulder abduction.
If you feel you may have a rotator cuff injury, your best bet, of course, is to seek professional medical attention and/or advice. In the meantime, if you are currently symptom free, the following exercises are a great place to start.
As always, be healthy and stay strong.
Common Ways to Injure The Rotator Cuff:
As with other muscles, the easiest way to injure a muscle (as in a tear or strain) is to apply a quick, sudden contractory motion to the muscle with too much force; especially when the muscle is cold. Think of trying to lift that 300 lb. barbell without any previous weightlifting training. In most cases, the result is less-than-stellar.
In the instance of most rotator cuff injuries, the culprit is usually overuse. Torn or strained rotator cuffs are common in people who perform a lot of overhead repetitive activities, such as window washing, painting, construction, etc. But when most people think of a rotator cuff injury, they picture the athlete, especially the pitcher and tennis player. But any sport or activity that requires a continual use of the rotator cuff draws a line nearer to injury.
The key I Have learned is to know what is normal for you. If you've done an activity in the past without pain and all of a sudden pain presents, then there may be an issue. It's often better to error on the side of caution and have things checked out. Quite often, minor rotator cuff injuries can be resolved without a surgeon's knife. And trust me, not having surgery is more tolerable to rehab.
In any case, I hope I've explained as simply as I could what the rotator cuff does, what muscles are involved, and how to better prepare yourself for injury prevention. Please feel free to leave comments and most of all, take care of yourself.
The greatest wealth is health as someone much wiser than me said.