Bursitis is inflammation of and liquid buildup within the bursa of a joint. The bursa is a lubricated cushion between the bone and soft tissue, which causes friction and pain when it is inflamed. Bursitis can occur in any joint in the body, but is most common in the shoulder, hip, elbow, and knee. When inflammation of a bursa is combined with infection, it is known as septic bursitis.

Repetitive movement, excessive pressure on a joint (such as kneeling), or traumatic injury can all cause bursitis. It is also linked to other conditions that affect the joints, such as rheumatoid arthritis, gout, or pseudogout. Treatment includes rest and NSAIDs, as well as antibiotics in the case of an infection.