A joint aspiration (arthrocentesis) is a test that involves
withdrawing (aspirating) a small sample of joint fluid from a
joint using a needle and syringe. Joints are where two bones
meet, allowing our bodies to move — the hips, knees, ankles,
elbows, shoulders, knuckles, etc. Joints contain synovial fluid,
which acts as a lubricant to help them move easily. In a joint
aspiration, a needle is carefully inserted into a joint space to
collect a sample of synovial fluid. Why It's Done Doctors
perform joint aspiration and examine the synovial fluid to
evaluate for suspected diseases or conditions in a joint. Joint
aspirations are most often done to help in the diagnosis and
cause of arthritis (inflammation of a joint). Arthritis can
cause redness, swelling, warmth, and pain in and around the
joint, and difficulty moving the joint. Septic arthritis is a
type of arthritis caused by an infection in the joint. It is
usually due to a bacterial infection in the joint. Joint
aspiration helps to diagnose this condition.