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Overview
Baker's cysts come with knee arthritis.
A clot must be ruled out.
When to get medical care
Call 911Not an emergency.
Get care todayCalf swelling, redness, or pain.
See a doctor soonLump behind the knee.
Causes
Caused by knee fluid.
OwieClear has pages on 2 conditions that can cause lump or swelling behind the knee. Each shows how soon to get care.
Common causes
- Baker's cystSee a doctor if it doesn't get better
A fluid-filled swelling behind the knee, often from arthritis or a knee injury.
Less likely causes
- Synovial sarcomaSee a doctor if it doesn't get better
A soft tissue cancer of teens and young adults, usually near a joint in the arm or leg, especially around the knee.
What you can do at home
- Rest.
- Ice.
Medicines
Treating knee problems.
At the doctor
Ultrasound checks.
Questions you may be asked
- Knee problems
The exam
A knee exam.
Tests
- Ultrasound
Prevention
Treat knee issues.
- Manage arthritis
Check your symptoms
Most symptoms have more than one possible cause. The symptom checker looks at all of your symptoms together, plus your age, and shows how soon to get care.
Sources
Last updated 2026-11-13.