Wherever your bones, tendons, and ligaments move against each other, particularly near joints, the points of contact are cushioned by small fluid-filled sacs called bursae.
By reducing friction, each of the more than 150 bursae in your body helps the joints operate smoothly through the full range of natural movement. But when a bursa becomes irritated and swollen, it's called bursitis -- or inflammation of the bursa.
When a joint is overused or injured suddenly, or when it remains under pressure for a long time, a nearby bursa can become inflamed. The sac fills with excess fluid, causing pressure on surrounding tissue. The first signal is pain, often accompanied by inflammation, swelling, and tenderness in the area. Bursitis is different from tendinitis, which is inflammation or irritation in the cord or tendon attaching muscle to bone.
Older age is associated with bursitis, and one of the most common places it strikes is in the shoulder, which has the greatest range of motion of all the body's major joints. The pain is generally felt along the outside top of the shoulder. The discomfort of bursitis tends to be most severe while using the joint but can also be severe at night. Other places that are prone to bursitis are the elbows, hips, and knees.
Bursitis often develops due to strenuous activity, particularly among the following types of people:
Manual workers. Heavy lifting, repetitive motion, or working for extended periods can strain the joints and bring on bursitis.
Athletes. They may get bursitis after running, throwing, or jumping, or from making aggressive arm swings in tennis, baseball, and even bowling.
Sedentary people. If they push their bodies past reasonable limits, they risk bursitis.