Patient question
The back of my knee feels swollen and tight when I bend it. Why?
Dr. Pablo GelberOrthopaedic Knee Surgeon
Quick answer
A tight, full feeling behind the knee when you bend it is often a Baker's cyst, a pocket of joint fluid pushed backwards by arthritis or a meniscus tear. Swelling that spreads into a painful calf is different and could be a blood clot, warns Dr. Pablo Gelber, knee surgeon at Aman Hospital in Doha, Qatar.
Why fluid collects at the back
When the knee makes extra fluid, some of it can be squeezed into a small pouch at the back of the joint, between the calf and hamstring tendons. This is a Baker's or popliteal cyst. It feels like a soft lump or tightness behind the knee, most noticeable when you bend fully, squat, kneel or sit on the floor, and it is often bigger at the end of the day.
A Baker's cyst is a sign of a problem inside the knee rather than a disease of its own. In adults the cause is usually osteoarthritis or a meniscus tear, especially at the back of the inner meniscus. Treating the underlying cause is what usually settles the cyst.
When it may not be a cyst
- Calf swelling, warmth, redness or tenderness, especially after a long flight, surgery or a period of immobility, can be a deep vein thrombosis and needs same-day assessment
- A ruptured Baker's cyst can leak fluid into the calf and cause sudden calf pain and swelling that looks very similar to a clot; only a scan can tell them apart
- A firm, growing lump that is not soft, or one with no knee problem behind it, should be scanned
- Pain behind the knee after a sudden push-off can be a hamstring or calf muscle strain
What helps now
Avoid deep bending, squatting and sitting cross-legged for a while. Ice and keeping the leg raised can ease the tightness. Gentle range-of-motion exercises and strengthening of the thigh muscles help the knee make less fluid over time. Do not massage a lump behind the knee if the calf is also swollen and painful until a clot has been ruled out.
Seeing a knee surgeon in Doha
At Aman Hospital Dr. Gelber examines the knee to find what is driving the fluid, often with an ultrasound to confirm a cyst and an X-ray or MRI to look at the cartilage and meniscus. Treatment is aimed at the cause: physiotherapy, activity changes, and in some patients an injection into the joint. Draining the cyst alone tends to bring only temporary relief. Surgery is reserved for a clear problem inside the knee, such as a torn meniscus that keeps catching.
Frequently asked questions
Will a Baker's cyst go away on its own?
It often shrinks or comes and goes as the knee settles. It is more likely to stay if the arthritis or meniscus problem behind it is ongoing.
Can children get a lump behind the knee?
Yes. In children a Baker's cyst usually occurs without any joint problem and often disappears without treatment, but it should still be examined once.
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