Tendonitis of the shoulder is an inflammation of the rotator cuff and/or biceps tendon. Shoulder tendonitis is usually the result of a tendon being pinched by surrounding structures. Shoulder tendonitis often occurs in certain sports that require the
arm to move over the head repeatedly, such as in baseball, weightlifting, racket sports, and certain swimming strokes. The injury may vary from mild inflammation to involvement of most of the rotator cuff.
When the rotator cuff tendon becomes inflamed and thickened, also known as rotator cuff tendonitis, it may get trapped under the acromion (the roof, or highest point, of the shoulder that is formed by a part of the scapula, or shoulder
blade).