Baker's Cyst (Popliteal Cyst)

What is a Baker’s Cyst?

A Baker’s cyst is a sac filled with clear fluid that forms on the back of the knee joint.

The cyst can vary in size from quite small – causing a feeling of fullness in the back of the knee to very large with a definite lump.

The cyst forms as a result of the fluid, which lines and lubricates the knee joint, escaping from the joint capsule. The sac itself is quite normal and will cause problems only when it becomes swollen with fluid.

Symptoms

• A painful or painless swelling behind the knee.
• Pain when bending and straightening the knee.
• Occasionally the cyst may rupture causing pain, swelling and bruising on the back of the knee and calf and it is often mistaken for a deep vein thrombosis (blood clot).

Causes

Any disease that affects the knee can lead to a Baker’s cyst.  For example:

• Inflammation
• Arthritis
• Ligament tears
• Cartilage injuries

Diagnosis

A physical examination is usually all that is needed to diagnose a Baker’s cyst. Further tests are not usually required unless the cyst has ruptured. An ultrasound will determine the presence of a Baker’s cyst.

Treatment

If the cyst is small and not causing much trouble, leaving it alone is safe. The cyst may resolve and disappear on its own.

There may be an underlying problem that needs further treatment.

The cyst may be drained or injected with cortisone.

Surgery is rarely required.

At Home

Follow the instructions given by staff about:

• Pain relief – You can take simple painkillers such as paracetamol, co-codamol or ibuprofen in line with manufacturers guidelines.
• Rest – elevate the affected leg and apply cold packs.

Activities

Avoid activities which cause you pain, for example, squatting, kneeling, heavy lifting, climbing and so on.

Continue with activities or movements which reduce your pain.

Prevention

There is no way to prevent a Baker’s cyst from forming and they can re-occur.

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