Shoulder impingement is a common problem, especially as we age. The protective pad called the bursa gets thin and even disappears in many adults. Without the proper space between the head of the humerus (upper arm bone) and the acromion (highest point of the shoulder), the shoulder tendons can get pinched as the arm is raised up.
Some patients don’t get better after treatment for impingement because the rotator cuff is torn as well. Your surgeon will be able to check the rest of the shoulder when the decompression is done.
Subacromial decompression removes some of the bone to make room for the soft tissues. It’s a very successful surgery for most people.