Tendinitis is inflammation, redness, soreness, and swelling, of a tendon. Tendinitis of the shoulder, whereby the rotator cuff or the biceps of the tendon become inflamed, is as a result of being strained by the surrounding structures. The injuries vary from slight inflammation to the involvement of the entire of the rotator cuff. The rotator cuff can be trapped under the acromion when it becomes inflamed or thickened.

The most common causes of tendinitis are overuse and a recurring movement from leisure activities, athletics, or work-related activities. Smoking, use of certain antibiotics like levofloxacin and ciprofloxacin can also lead to the development of tendonitis. Diseases such as rheumatoid arthritis, obesity and diabetes can cause tendinitis. The inflation of bursa sacs which protects the shoulder, bursitis, can be accompanied by tendinitis and impingement syndrome. Activities that involve overuse of such as in sports and occupations that require overstretching of the shoulder in order to reach a certain height, these activities are potential causes of irritation to the rotator cuff and bursa which may lead to impingement hence cause bursitis.

Age is also a common factor that leads to bursitis. Repeated motion which involves the arms for a long period of time irritates and wears down the tendons, muscles and surrounding structures. There are quite distinctive signs and symptoms that a person could use to know that he/she is suffering from either tendinitis or bursitis. Sometimes one can raise his/her hand above the head and feel like the shoulder is making some kind of sounds and it is accompanied by sharp pain which subsides moments after the hand is brought down. A person who is suffering from tendinitis and bursitis will have problems sleeping on the affected shoulder because there will be a development of discomfort and pains on the upper shoulder or the upper third of the arm.