The most common causes of bursitis are repetitive motions (for example, repeated throwing of a ball), trauma (extensive kneeling or hitting your knee on a table), infection, and preexisting rheumatoid conditions.

    Trauma Trauma causes inflammatory bursitis from repetitive injury or direct impact.

    Chronic bursitis: The most common cause of chronic bursitis is minor trauma that may occur to the shoulder (subdeltoid) bursa from repetitive motion, for example, throwing a baseball. Another example is prepatellar bursitis (in front of the knee) from prolonged or repetitive kneeling on a hard surface to scrub a floor or lay carpet.

    Acute bursitis: A direct blow (let's say you accidentally bang your knee into a table) can cause blood to leak into the bursa. This causes inflammation with pain as well as swelling.

Infections

    Bursae close to the surface of the skin are the most likely to get infected with bacteria, a condition that is called septic bursitis. The most common bacteria to cause septic bursitis are Staphylococcus aureus or Staphylococcus epidermis. People with diabetes, alcoholism, certain kidney conditions, those with suppressed immune systems such as from cortisone medications (steroid treatments), and those with wounds to the skin over a bursa are at higher risk for septic bursitis. About 85% of septic bursitis occurs in men.

Rheumatoid conditions

    People with certain rheumatoid diseases such as gout and pseudogout can develop bursitis from crystal deposits. When these crystals form in a bursa, they cause inflammation leading to bursitis.