What should you know about a red, warm, swollen knee?

Swelling may be fluid inside the joint or in tissues around it. Gout can cause sudden intense inflammation, while knee bursitis affects a fluid-filled cushion near the joint. A knee injury such as an ACL or meniscus tear may produce swelling after a twist or impact. Osteoarthritis more often causes activity-related aching and stiffness, although a hot red flare needs review. Infection is less common but urgent, particularly when fever, chills, marked pain, or difficulty moving the knee accompanies the redness.

Rest from running, jumping, and heavy loading. Keep the leg raised when resting, and use a wrapped cold pack for short periods if that feels comfortable. Do not massage a hot swollen joint or force it through painful movement. Note when the change began, whether there was an injury, and whether you have fever or a wound nearby. A clinician may examine the knee and, when fluid is present, consider joint aspiration to test or relieve it.

Seek urgent care today if the knee is hot and very painful, you feel unwell, have fever, cannot bear weight, cannot bend or straighten it, or the swelling appeared rapidly after an injury. Go to emergency care for confusion, faintness, severe weakness, or rapidly spreading redness. Even without these warning signs, arrange an assessment soon if swelling persists or repeatedly returns.

Ask whether the fluid is inside the joint, whether infection or gout needs testing, and which movements are safe while it settles. Ask what symptoms should prompt a same-day review and when you can gradually resume normal activity.