Possible causes of an elbow sac filling with fluid include injuries, overuse, pressure, infection and chronic medical conditions, such as rheumatoid arthritis, according to Drugs.com. This condition is called elbow bursitis and causes pain, warmth, redness and swelling in the elbow area.
Although the elbow sac, or bursa, normally contains a small amount of fluid, falling on an elbow or overusing an elbow in regular activities, such as tennis, can cause inflammation, which increases the fluid in the elbow sac to an uncomfortable level, explains the American Academy of Orthopaedic Surgeons. The increase in fluid causes pain and a reduced the range of motion in the joint. Frequently leaning on the elbows can also cause fluid accumulation and irritation.
Sometimes bacteria enters the elbow sac, usually through a break in the skin or a bug bite, notes the American Academy of Orthopaedic Surgeons. In addition to swelling, a bacterial infection typically causes redness and warmth in the skin covering the elbow. Bacterial infections need to be treated with antibiotics to avoid serious complications. Swelling in the elbow without an obvious cause might be a symptom of gout or arthritis. A physical examination, along with blood tests, an X-ray or an MRI, helps doctors diagnose the cause of elbow bursitis.