The Shoulder Joints
Yes, you read that correctly. It’s shoulder joints plural as the shoulder is one of the most complex joint systems in the body. The multiple joints and muscles that together form what we know as “shoulder” have to work together seamlessly to achieve overhead movements. Due to its intricacy, the shoulder is vulnerable to breakdown at several different parts of the chain all of which can lead to pain in the shoulder.
The shoulder joint is made up of three main bones; the clavicle, the scapula, and the humerus. These three bones create the 4 joints of the shoulder girdle; sternoclavicular joint, acromioclavicular joint, glenohumeral joint, and the scapulothoracic joint.
The Art of Overhead Movement
All of these joints must move in unison with full range of motion to achieve overhead movements. To illustrate the complexity of this system, you’ll find a numbered play-by-play of what happens at each joint during shoulder abduction (the motion involved in lifting your arm out to the side and up overhead).
For reference, an overhead shoulder press, pull up, and extended side angle in yoga are examples of movements that require full shoulder abduction.
- There is a combination of humeral movement and scapular upward rotation to achieve the full 180 degrees required for full abduction. This means that as the arm moves up and out to the side, the scapula must also upwardly rotate 60 degrees.
- The sternoclavicular joint will elevate and your acromioclavicular joint will upwardly rotate
- The clavicle retracts and rotates at the sternoclavicular joint
- The scapular also tilts posteriorly and externally rotates
- The upper back or thoracic spine must extend 20-30 degrees
- Lastly, the glenohumeral joint must externally rotate.
Astonishingly, all of these motions need to take place at the same time within your shoulder for you to achieve the simple task of reaching over your head. If any one of these joints are restricted, this will lead to shoulder impingement.
So What is Shoulder Impingement??
Shoulder impingement is when the subacromial space (the area between your acromion and humeral head) is reduced or compressed. In a healthy individual, the subacromial space is only 1 centimeter wide and contains your supraspinatus tendon, bicep long head tendon, and subacromial bursa.
Due to the already limited amount of space in this region, inflammation and irritation to these structures can happen very quickly if our shoulder girdle isn’t moving with correct, fluid biomechanics.
The Shoulder Muscles
Now that we’ve covered the joint mechanics, let’s talk about the muscles responsible for ensuring these joints move correctly. The main muscles in the shoulder complex are the rotator cuff, serratus anterior, rhomboids, and trapezius muscle.
The Rotator Cuff Muscles
The rotator cuff, comprised of the supraspinatus, infraspinatus, subscapularis, and teres minor muscles, works to keep your humeral head seated in your scapular glenoid and provides stability to the glenohumeral joint. If they are underperforming or weak, this can cause superior translation of the humerus into the acromion and cause shoulder impingement.
Press play below a great exercise to keep your rotator cuff strong and firing:
The Serratus Anterior Muscle
The serratus anterior muscle is in charge of ensuring full upward rotation of the scapula with overhead shoulder movements. If your shoulder blade isn’t upwardly rotating all the way, this also causes narrowing of the subacromial space and can lead to impingement.
Here is my favorite exercise to get your serratus anterior firing:
The Posterior Scapular Chain Muscles
Lastly, your rhomboids and middle/lower trap muscles work with your serratus anterior to provide stability to your scapula. The trapezius muscles help with upward rotation of the shoulder blade and work with the rhomboids to help to keep the scapula in an appropriate position throughout shoulder movement. This muscle group is often referred to as your posterior scapular chain and is important for shoulder stability.
Here is a great posterior scapular chain exercise:
The Take-A-Way Points For A Healthy Shoulder
The combination of complex joint and muscle coordination in your shoulder puts it at high risk for injury. If you do a lot of upper extremity activities, the exercises depicted in this article are great if you have an acute injury, or if you simply want to focus on injury prevention.
Some people may need a little extra help, which is where physical therapy comes into play. As physical therapists, we can make sure each component of the shoulder complex is moving appropriately as well as use techniques to promote proper muscle activation.
If you’re curious about how to get your shoulder feeling better fast or you’d like to learn about your options to break the cycle and get lasting relief, talking with a Doctor of Physical Therapy is a great place to start.