What are the causes for Bursitis?

A bursa can become inflamed from injury, infection (rare in the shoulder), or due to an underlying rheumatic condition. Examples of bursitis include injury as subtle as lifting a bag of groceries into the car to inflame the shoulder bursa (shoulder bursitis), infection of the bursa in front of the knee from an abrasion or puncture wound (septic prepatellar bursitis), and inflammation of the elbow bursa from gout crystals (gouty olecranon bursitis). Sometimes tendonitis occurs associated with bursitis, especially in the shoulder.

Source: http://www.emedicinehealth.com