Baker's cyst or meniscal cyst: what is the lump on my knee?

The short verdict

Both are fluid-filled and usually harmless, and both are signs of something happening inside the knee rather than a separate disease. The main differences are where they sit and what drives them. A Baker's cyst behind the knee is a pocket of joint fluid pushed backwards. A meniscal cyst at the side of the knee forms when fluid escapes through a tear in the meniscus and collects next to it.

How they compare

• Location: Baker's cyst is behind the knee, often on the inner side of the back; meniscal cyst is on the side of the knee at the joint line, more often on the outer side
• Feel: a Baker's cyst is soft and may change size; a meniscal cyst is usually smaller, firmer and tender to press
• Size changes: a Baker's cyst often feels tighter when the knee is straight; a meniscal cyst may be more obvious with the knee slightly bent
• Cause: Baker's cysts follow arthritis, meniscus tears or inflammation; meniscal cysts follow a horizontal meniscus tear
• Diagnosis: ultrasound or MRI confirms both, and MRI shows the tear behind a meniscal cyst
• Treatment: Baker's cysts often settle when the knee problem is treated; meniscal cysts may need the tear treated, sometimes with keyhole surgery and decompression of the cyst

Who each tends to affect

Baker's cysts tend to affect adults over 40 with knee arthritis or a degenerative meniscus tear, and people with inflammatory arthritis. Meniscal cysts tend to affect active adults with a horizontal tear, often after years of squatting, twisting sports or manual work. Children can have Baker's cysts too, usually without a knee problem behind them, and these often settle on their own.

When to see a knee surgeon in Doha

Book an assessment if a lump is growing, painful, or limits bending, praying or sitting on the floor. Seek urgent care if your calf suddenly becomes painful and swollen, because a ruptured cyst and a blood clot can look alike and a clot must be ruled out. Dr. Gelber at Aman Hospital will examine the lump, arrange an ultrasound or MRI if needed, and treat the cause.