A joint effusion is an abnormal build-up of synovial fluid inside a joint capsule, causing visible swelling, warmth and a tight, fluid-filled feeling. It can follow injury, osteoarthritis flares, inflammatory arthritis, gout, pseudogout or infection. Clinicians may aspirate (draw off) the fluid with a needle both to relieve pressure and to test it — checking cell count, crystals and culture — before deciding on treatment such as a steroid injection, urate-lowering therapy or antibiotics.
What is joint effusion?
Joint effusion: A joint effusion is abnormal accumulation of fluid inside the joint capsule, causing visible swelling, tightness and reduced movement. Common in OA, RA, gout, trauma or infection. May be drained (aspirated) to relieve symptoms and analyse the cause.
Last updated 2026-07-04. This is general information, not a substitute for personalised medical advice.