Subacromial/Subdeltoid bursitis is an inflammation of the subacromial or subdeltoid bursa, a small fluid-filled sac that cushions the space between the rotator cuff tendons, shoulder muscles, and the acromion. When the bursa becomes inflamed, it causes pain and restricts smooth shoulder movement. This condition commonly develops due to repetitive overhead activities, shoulder impingement, injury, or overuse, and may occur alongside rotator cuff disorders.