The shoulder is the most complex joint in the body, but it did not come with an owners manual. So, here’s a quick run down on shoulder anatomy and function. Knowing the basics will help tremendously when you’re trying to fix your own shoulder problems. This guide will explain the parts of the shoulder and describe “optimal” use of the arm.
We have an entire series on the shoulder and you can start with what to do with a freshly injured one.
Basic Shoulder 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 sitting on a golf tee wrapped tightly in a bed sheet (capsule)
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. The joint is able to move through a large range of motion at the expense of stability. That large range of motion is in front of you, not to the side, because of where the shoulder joint is located. Most pain you feel happens outside the scapular plane because it’s when the shoulder joint has the least support. The muscles around the shoulder blade are the most important for shoulder function, and all rehab programs target this area.