What should you know about painless swelling in knee?

Fluid may collect inside the knee joint or in a nearby sac. A Baker's cyst often appears as fullness behind the knee. Knee bursitis may cause a more localised lump over the kneecap. Osteoarthritis can gradually produce swelling and stiffness, while a meniscus tear or ACL tear may follow a twist and cause catching or instability. Gout often brings marked pain and warmth, so painless swelling is not its typical presentation. The side, firmness, duration, and ability to bend the knee help distinguish these patterns.

Compare both knees and note whether swelling changes after walking, kneeling, or rest. Reduce activities that increase fullness, keep gentle range-of-motion movements, and elevate the leg when resting. Do not puncture or massage a new lump. A clinician may examine the joint and, when fluid is substantial or the cause is unclear, discuss imaging or joint aspiration to analyse or relieve fluid.

Book an assessment if swelling persists, returns, limits bending, or follows an injury. Seek urgent care if the knee becomes hot and red, you develop fever, the calf also swells, or you cannot bear weight. Sudden swelling after a twist with locking or giving way also warrants prompt evaluation.

Is the fluid inside the joint or in a bursa or cyst? Do I need imaging or aspiration? Which activities and exercises are appropriate while the swelling is present?