Many people suffer with shoulder, upper back, and neck issues. They blame the arm, neck, or an assortment of tight muscles in their upper back. Very few of them consider the scapula.
The scapula (shoulder blade) is definitely an “out of sight, out of mind” part of the body. But it’s relevant to many upper body aches and pains. A more posturally aware person may ask if having a “low shoulder” is part of the problem. What they are really referring to is the position of the scapula and rib cage.
Go ahead and look closely at your own shoulders.
–Waits for your return to read on…-
The far majority of you will see that the dominant side does sit lower than the other. This is a sign of serious scapular discombobulesis, and requires physical therapy minimally 3 times per week for 70 X 7 weeks.
Seriously though – is a low shoulder truly an issue when it comes to neck, shoulder, or arm pain? There is much to be said regarding differential diagnosis of common posture problems and corrections, all the way down to the pelvis. But here are the basics of what you need to know.
Having one side sit lower than the other is usually not a problem. It’s quite normal and I have yet to read a satisfactory explanation as to why this happens.
There are exceptions, of course. One shoulder may appear elevated when there is severe spinal scoliosis or a pinched nerve in the neck. The muscles reflexivily shorten, pulling the scapula upward in order to allow more room for the nerve. Patient’s with this pattern often feel tight in their neck and upper shoulder. When they try stretching the muscles it makes their nerve symptoms worse. The muscle is not tight but in protective spasm, and in this instance it is important to treat the nerve issue and postural motor control issues before trying to lower the scapula by stretching it “down.”
Know your scapula!
Uneven shoulders should be observed in a few planes. Movements of the scap include:
-elevation (gliding up) and depression (gliding down, this is normal on the dominant arm)
-upward and downward rotation
-internal and external rotation ( as in pinching the shoulder blades together forward and backward)
-flexion and extension (tilting forward and tilting backward)
The main point is that shoulder blade flexion with downward rotation is a very common pattern causing what appears to be a “low shoulder.” Sooner or later, this type of “low shoulder” is likely to cause problems at the shoulder joint, the neck and mid to upper spine area. A few of the most common causes of this flexed, downward position include:
-habitual, chronic sitting postures
-repetitive stress up that is due to asymmetry of the pelvis and spine
-repetitive stress through our arms, as in throwing or reaching
Each of these low shoulders would obviously be treated differently.
Here is an example of scapular depression (almost universal and usually not a problem) :
This guy has some serious upper body size with fairly even shoulder blades. His dominant arm sits in depression and this is likely not an issue.
Here is an example of scapular downward rotation (commonly problematic):
The black line indicates where the medial border of the shoulder blade should sit, and the red line indicates how it is sloping down and forward. 
This fellow better get some essential oils right now, because it’s just a matter of time before impingement of the rotator cuff or shoulder bursa, or muscle strain takes place. Seriously though, this athlete should address his scapula position and mechanics (the photo does not show what happens when he moves the arm) prior to:
Repetitive throwing or striking overhead
Repetitive rotation of the arm back behind the body.
Resistance training with overhead movements such as shoulder presses.
Both images display a “low shoulder” and are only subtly different. But the treatment and expected outcome are not the same.There are other sub-types of scapular position and dysfunctional movement. But for now, those with neck, upper back, and arm pain need to at least consider the role of the scapula in these problems.
Biomechanical eggheads may be interested in this.
And Gru has some serious postural issues. 
Bonny Lane Club 