Bursitis is caused by repeated actions or positions that inflame the bursae in a joint, for example, leaning on the elbow or sitting on hard surfaces for a long period. It may also be caused by an injury, an infection and inflammatory arthritis, as stated by Mayo Clinic.
Bursae are small sacs in the joints that become inflamed when the joints are overused. This causes them to be filled with fluids, causing pressure on nearby body tissue and resulting in pain, swelling and inflammation, as stated by WebMD. People who have a higher risk of getting bursitis include athletes, sedentary people and manual workers.