For most of my life, I assumed the shoulder automatically worked together as a unit. It doesn’t take too much studying of the human anatomy to understand this is a bad assumption. Most players, right-handed, try to turn their left shoulder away from the target on the backswing. As stated before, this does not indicate that the right shoulder rotates away from the target line. Each shoulder has a complex system of muscles and tendons that control their motion. They both work independently by using p[rimarily using the rotator cuff. 
So both shoulders can go into extension and retraction during the swing. Right-handed players extend their left shoulder on the backswing and retract the shoulder on or about ball impact and in the follow-through. The right should works in the complete opposite cycle as the left.
So the question is, can you get a 90-degree shoulder turn without retracting your trail, right shoulder………doubtfull unless you have a hypermobile thoracic spine. Go to the range or nearest practice facility and try to learn how to turn your trail shoulder away from the target line. If this is as uncomfortable for you as it was to me this indicates you have not been doing this, especially in pressure situations.
Notice how far back the right should has rotated….
You wont get your right shoulder where DJ does unless you rotate your right shoulder and your left shoulder.
This one is for you mom!
This will initially make your swing feel out of control but will quickly become manageable. You will also find much of the distance you have been missing.
Play good and practice hard.
Jim Hartnett, PGA
