The rotator cuff muscles hold the ball in the shoulder socket throughout movement. You need to train these muscles to fire correctly in whatever range of movement is painful, although the exercise itself should be completely pain free. 

This exercise from our Shoulder Series shows you how to do this.

Check out the earlier videos in the shoulder series (#12, #13, #14, #18, #18.2) before taking on this one to ensure you’ve learned the best position and movement techniques.