How it works: Shoulder Anatomy
The owners manual you didn't know you needed
The shoulder is the most complex joint in the body, but it did not come with an owners manual.
Here’s a quick lesson on shoulder anatomy and function
Knowing how your shoulder works is a cheat code when you are trying to avoid pain and correct a shoulder issue.
This guide will explain the parts of the shoulder and describe “optimal” use of the arm.
You’ll also see how to grab our Shoulder Rehab Program for free
If you just hurt your shoulder be sure to check our post on what to do so you don’t turn a short term problem into a long term problem
Basic Shoulder Joint Anatomy
The shoulder is a ball and socket joint and one of the most complex joints in the body. It is not a true ball and socket since the stability is from the soft tissue (tendons, ligaments, etc) interwoven into the capsule.
The design allows a lot of motion at the expense of stability. You can visualize the shoulder as a baseball (humeral head) sitting on a golf tee (glenohumeral joint) wrapped tightly in a bed sheet (capsule)
I use baseball on a golf tee to highlight size difference
Joints Around the Shoulder
The ball on the tee = the glenohumeral joint (GHJ). It’s the most well known joint, but is a small portion of shoulder anatomy. The other joints are listed in the picture below.
The most important joint in the complex is the scapulothoracic joint, where the shoulder blade attaches to the body. This joint is the focus of most rehab programs.
It also isn’t a true joint and “floats” on the body via connections from 17 different muscles, adding to the complexity. The neck, upper back, and low back all affect scapulothoracic joint position.
The Scapular Plane
The most important thing to recognize regarding shoulder anatomy is the location of the GHJ. It’s at a 35-45 degree angle from the body. Note it is a range, not an absolute position.
This is usually very enlightening to most folks. You can make a 360° arc with the arm, but that motion is to the front, NOT to the side.
The scapular plane is the most efficient position for the shoulder and you get the “ideal” contribution from all the joints and muscles.
Most shoulder pain occurs OUTSIDE this plane, for a variety of reasons.
The pain does not mean damage, but you are forcing the GHJ to do a majority of the work without help from the scapulothoracic joint.
Shoulder Blade Anatomy and Function
The shoulders make a bunch of different motions with specific names, but upward rotation and protraction (circles below) are the most important in regards to arm movements. The primary being upward rotation.
Upward rotation creates arm movement, and the other motions support that. How much of each you get of the other motions depends
your posture
the task you are doing
Shoulder Anatomy Summary
This was a very oversimplified lesson on shoulder anatomy. Here are the highlights:
The joint is not a true ball and socket and stability is from the capsule
The scapular plane provides the “optimal” balance of musculature for tasks
The most important joint for the shoulder is the scapulothoracic joint, or where the shoulder blade attaches to the body
The scapulothoracic joint is a “floating” joint and nearly 20 muscles affect its function
Most rehab programs (should) target the scapulothoracic joint
Shoulder stability is position depending - your posture and the tasks will dictate the “optimal” way to move
Grab your free Program
We’ve included our shoulder rehab program (plus the others) as part of our Substack subscription.
We’ve been treating shoulders for over a decade.
We’ve figured out what works, distilled it all into our program. There’s no need to come see us, we can come to you.
Grab the program below.