The shoulder joint allows the arm to move in multiple directions. Along with this, we use our arms to do a lot of things in daily life. These two factors alone can lead to a range of shoulder injuries and shoulder pain.
There are also a number of other factors that increase the risk of shoulder injuries such as posture, muscular imbalances, hyper mobility to name a few.
The most common shoulder injuries are subacromial shoulder impingement, frozen shoulder (adhesive capsulitis) and osteoarthritis of the joint. I have written rehabilitation programmes on these three along with a general shoulder pain treatment plan for those with general pain and no traditional "injury".