A hot or swollen knee: when is it more than a strain?

Compare the knee with your other one: is it newly larger, warmer, painful to touch or harder to bend? Did it swell after a twist or fall, or without an injury you remember? Note how quickly it changed and whether you can stand and walk. Redness can be harder to notice on brown or dark skin, so warmth, swelling and the way the joint moves matter too.

The NHS lists several possible reasons for a warm or swollen knee, including bursitis, bleeding into the joint, gout and infection. A history of kneeling might fit bursitis, but it cannot rule out another problem. An online symptom guide cannot examine the joint or decide whether there is fluid inside it.

Get urgent in-person medical advice today if the knee is very painful, badly swollen or has changed shape, or you cannot move it or put weight on it. A hot or red knee with fever, feeling hot and cold, or shivering is especially concerning for infection. NHS guidance says joint infection can develop quickly and needs prompt treatment; not everyone with it has a fever. Do not wait at home for every warning sign to appear.

If a clinician suspects a joint infection, examination and tests may be needed; sometimes fluid is taken from the joint. That is a clinical decision, not something you can establish from a photograph. If you cannot travel safely because you cannot bear weight or you feel very unwell, use local urgent or emergency medical services rather than finishing a questionnaire.

For a mild new knee pain without the warning signs above, the NHS suggests reducing weight on the joint and a cold pack wrapped in cloth for short periods. But home measures should not delay assessment of a hot, badly swollen or rapidly worsening knee. Do not force a painful joint to bend to see whether it will loosen up.

At the visit, say when the swelling started, whether there was a fall or long kneeling shift, whether you have fever or shivers, and how far you can walk now. Mention a recent wound, joint surgery, an artificial joint or a condition such as diabetes if relevant. Our knee guide can help organise a non-urgent history; its result cannot distinguish bursitis from infection.