Not sure about you, but I tend to protect my chest and scar without even being aware of it. I round my shoulders and flex at my back to create a rounded posture. This is not good. It provides less space for the lungs and puts too much stress on your neck and shoulders. This type of posture can leave you vulnerable to shoulder injuries. Here is one exercise to help. The works the lower and middle trapezius. Thumbs must point up and arms should be about 45 degrees off the mid line.
Try this exercise!