I hurt my knee and it is swollen: what should I know?

Knee swelling can develop quickly after a twist, landing or collision, or build gradually after repeated loading. The knee may fill with fluid because tissues inside the joint are irritated or injured; swelling can also come from a bursa or a problem behind the knee. A knee injury with a pop, instability or difficulty straightening can involve structures such as an [ACL Tear](/conditions/acl-tear/) or [Meniscus Tear](/conditions/meniscus-tear/).

Swelling with warmth and intense tenderness may also occur with [Gout](/conditions/gout/), bursitis or infection. The symptom does not identify one cause by itself, so timing, examination and sometimes imaging matter.

Stop the activity that caused the pain and protect the knee from twisting or impact. Rest it in a comfortable position, use a cold pack wrapped in cloth for short periods if that feels helpful, and keep gentle movement within a tolerable range. Do not forcefully massage a freshly injured swollen knee or return to sport while it gives way.

Arrange an examination to check stability, range of motion and the source of fluid. [Joint Aspiration](/treatments/non-surgical-orthopedics/joint-aspiration/) is a procedure a clinician may consider in selected cases to remove or test joint fluid; it is not needed for every swollen knee.

Get urgent medical help if the knee is visibly deformed, you cannot bear weight, swelling appeared rapidly after major trauma, or the joint is hot with fever or feeling unwell. Seek prompt assessment for a locked knee, new numbness, a cold or pale foot, severe calf swelling, or worsening pain. A persistent or recurrent swelling also warrants review.

Ask whether the swelling is inside the joint or around it, which injury structures need testing, and whether you need imaging or protected weight-bearing. Ask when bending, driving, work and sport can be resumed safely.