What is it?
Fluid collects behind the knee, often because of an underlying joint problem such as arthritis or a meniscal tear.
Symptoms and important signs
Fullness or tightness behind the knee; rupture may cause calf swelling.
How is it assessed?
Examination and sometimes ultrasound; assess the underlying knee problem.
Care and treatment options
Treat symptoms and the underlying cause. Aspiration or surgery is not always needed.
When to seek help
Sudden calf swelling needs assessment for a blood clot, not an assumed cyst rupture.