Swelling near the knee joint: what to know

Swelling after a twist or impact may reflect a sprain, cartilage problem, or fluid inside the joint. A soft bulge at the back or beside the knee can involve a bursa or a fluid-filled sac. Sudden intense pain with a hot, red joint can occur with gout or pseudogout, while osteoarthritis often causes activity-related aching and stiffness. Psoriatic arthritis and rheumatoid arthritis can produce inflammatory swelling, stiffness, and symptoms in more than one joint. A knee that is hot with fever needs prompt assessment because infection must be considered.

Reduce impact and deep bending for now, rest with the leg supported, and use a wrapped cool pack for short intervals if swelling followed activity or injury. Keep the knee moving gently within comfort so it does not become stiff. Do not try to drain the swelling yourself. A clinician may examine stability, range of motion, skin temperature, and other joints; tests can distinguish fluid, injury, crystal inflammation, or infection. Treatment may include an anti-inflammatory medication or, in selected cases, a cortisone injection after assessment.

Seek urgent care if you cannot bear weight, the knee is deformed or locked, swelling appeared rapidly after trauma, or the calf becomes swollen with chest pain or breathlessness. Get same-day medical advice for a hot, red, very painful knee, fever, or feeling unwell. Arrange an appointment for recurring swelling, persistent stiffness, or pain that changes your walking.

Is the fluid inside the joint or in a nearby bursa? Could crystals, arthritis, or infection explain the pattern? What activity is safe while the knee is swollen, and which treatment suits my medical history?