Red, Swollen and Hot Knee: What It May Mean

Heat, redness and swelling indicate active inflammation around or inside the joint. Gout can present with sudden intense inflammation, while knee bursitis affects a fluid-filled cushion near the joint. A Baker's Cyst may cause fullness behind the knee. Knee osteoarthritis can flare, and an ACL Tear or Meniscus Tear may cause swelling after an injury, although marked heat and redness need separate attention.

A symptom does not identify one diagnosis by itself. A clinician may examine the skin and joint, ask about injury and fever, and decide whether blood tests, imaging or fluid testing is appropriate.

Rest from strenuous activity, keep the leg comfortably raised, and use a cool pack wrapped in cloth for short periods. Avoid forceful massage or putting weight through a painful knee. Do not start leftover antibiotics or inject medication without medical advice.

Depending on the cause, treatment may include medicine, wound care or [Joint Aspiration](/treatments/non-surgical-orthopedics/joint-aspiration/) to examine or remove joint fluid. Read about [Knee Swelling](/symptoms/knee-swelling/) while arranging care.

Seek urgent medical care today if the knee is hot and red with fever, chills, rapidly increasing swelling, severe pain, inability to bear weight, or feeling faint or confused. Immediate assessment is also needed after a wound, injection or operation if redness is spreading or fluid is draining. Do not wait for symptoms to settle when infection is possible.

Ask what findings point toward infection, gout, bursitis or an injury; whether joint fluid should be tested; and which pain medicines are safe with your medical history. Clarify what change should trigger emergency review.