What does knee swelling feel like with septic arthritis?

Septic arthritis is an infection inside a joint. In the knee, inflammation and fluid can create rapid swelling, marked tenderness, and pain with even small movements. The skin may look red or feel hot, and putting weight through the leg may be extremely difficult. Fever, chills, tiredness, or feeling generally unwell can occur, but their absence does not safely rule out infection.

Knee swelling has many possible causes, and only an examination and appropriate tests can identify the source. Read the symptom overview for [Knee Swelling](/symptoms/knee-swelling/).

Do not massage the swollen knee, exercise through severe pain, or delay assessment to see whether it settles. Contact urgent medical services or go to an emergency department for a hot, rapidly swollen, very painful knee, particularly if movement or weight-bearing is difficult. Tell the clinician about recent surgery, injections, wounds, or immune problems.

Seek immediate care when severe knee pain and swelling develop with heat, redness, fever, chills, or feeling unwell. Prompt treatment matters because an infection can damage the joint and affect the wider body.

Ask what tests are needed to check for infection, whether fluid should be sampled, and which treatment should begin while results are being reviewed. Mention the exact onset and any recent procedure or skin infection.