The shoulder is the most mobile joint in the body and is comprised of multiple intricate muscles, tendons, and bones that come together to allow you to move your arm in many different ways. When these muscles or tendons are injured or bones are out of alignment it can cause different types of shoulder pains. Some of the most common causes of shoulder pain are rotator cuff injury or tear, shoulder impingement, tendonitis, and poor posture. For more causes of common shoulder pain check out the link below.