Most shoulder problems fall into four major categories:
Tendon inflammation (bursitis or tendinitis) or tendon tear
Instability
Arthritis
Fracture (broken bone)
Other much less common causes of shoulder pain are tumors, infection, and nerve-related problems.
Bursitis
Bursae are small, fluid-filled sacs that are located in joints throughout the body, including the shoulder. They act as cushions between bones and the overlying soft tissues, and help reduce friction between the gliding muscles and the bone.
Sometimes, excessive use of the shoulder leads to inflammation and swelling of the bursa between the rotator cuff and part of the shoulder blade known as the acromion. The result is a condition known as subacromial bursitis. Bursitis often occurs in association with rotator cuff tendinitis. The many tissues in the shoulder can become inflamed and painful. Many daily activities, such as combing your hair or getting dressed, may become difficult.
Tendinitis
A tendon is a cord that connects muscle to bone. Most tendinitis is a result of a wearing down of the tendon that occurs slowly over time, much like the wearing process on the sole of a shoe that eventually splits from overuse.
Generally, tendinitis is one of two types:
Acute. Excessive ball throwing or other overhead activities during work or sport can lead to acute tendinitis.
Chronic. Degenerative diseases like arthritis or repetitive wear and tear due to age, can lead to chronic tendinitis.
The most commonly affected tendons in the shoulder are the four rotator cuff tendons and one of the biceps tendons. The rotator cuff is made up of four small muscles and their tendons that cover the head of your upper arm bone and keep it in the shoulder socket. Your rotator cuff helps provide shoulder motion and stability.