An abnormal build-up of fluid within or around a joint.
Effusion refers to excess fluid accumulation within a joint capsule (or, less commonly in this context, surrounding tissues such as the pleural or bursal spaces), typically as a reactive response to injury, inflammation, or synovial irritation. In sports medicine it most often denotes joint effusion (e.g., knee, ankle, elbow), detected clinically via swelling, ballotement, or the sweep test, or confirmed with imaging such as ultrasound or MRI. It is a nonspecific sign — presence and volume can indicate the reactivity of an underlying pathology but do not by themselves confirm a specific diagnosis.
This guide was auto-drafted and is pending editorial review.