Biomechanically the pelvis and shoulder are linked. This is what is referred to as a Myofascial sling.
The hamstrings starting from the tibia then insert into the Ischial tuberosity. This then continues along as the Sacro-tuberous ligament and then through the thoraco-Lumbar fascia. This then continues to the Latissimus dorsi which then inserts into the opposite scapula and humerus.
Therefore your Hamstrings actually attach to your arms!!!
So....if there is tension through this sling caused from a rotated pelvis, then the infraspinatus (a muscle on the scapula) can go into spasm and so prevents the biomechanical function of the shoulder. This is a common cause of shoulder injuries.
In order to reduce risk of shoulder injuries the pelvis must be in good biomechanical shape.
Therefore if you have shoulder pain, then you will need to have your pelvis assessed.
I'm really not going crazy if I assess your pelvis before looking at your shoulder!
Image: Thomas Myers Anatomy Trains