A Baker’s cyst (also known as a popliteal cyst) is a fluctuant swelling located in the popliteal space. The term is a misnomer as the swelling is the result of synovial fluid distending the gastrocnemio-semimembranosus bursa, rather than being a true cyst. In older patients it is commonly part of a chronic knee joint effusion which herniates between the two heads of the gastrocnemius and is most commonly secondary to degenerative or meniscal pathology.
Secondary cysts communicate freely with the knee joint and contain fluid of normal viscosity. They are thought to be caused by a combination of weakness around the knee, internal pathology and valvular opening between the knee joint and bursa. These types of cysts occur in older people, often cause symptoms and are associated with underlying articular disorders.
A Baker’s cyst is caused by swelling in the knee. The swelling is due to an increase in the fluid that lubricates the knee joint (synovial fluid). When pressure builds up, fluid bulges into the back of the knee.
Baker’s cyst commonly occurs with:
- A tear in the meniscal cartilage of the knee
- Knee arthritis (in older adults)
- Rheumatoid arthritis
- Other knee problems
A large cyst may cause some discomfort or stiffness, but there are often no symptoms. There may be a painless or painful swelling behind the knee.
The cyst may feel like a water-filled balloon. Sometimes, the cyst may break open (rupture), causing pain, swelling, and bruising on the back of the knee and calf.
It is important to know whether pain or swelling is caused by a Baker’s cyst or a blood clot. A blood clot (deep venous thrombosis) can also cause pain, swelling, and bruising on the back of the knee and calf. A blood clot may be dangerous and requires immediate medical attention.
Complications are rare, but may include:
- prolonged swelling
- severe pain
- complications from related injuries, such as torn cartilage
Your doctor will examine your knee and ask you questions about your past health and when the pain and swelling started. Your doctor may order tests, such as an MRI, to see a picture of the inside of your knee.
A Baker’s cyst may go away on its own.
If arthritis or another problem is causing the Baker’s cyst, your doctor may treat that problem. This usually makes the pain and swelling of a Baker’s cyst go away.
If a cyst does not go away, or if it is causing a lot of pain, your doctor may drain the fluid with a needle. You also may be given a shot of steroid medicine to reduce swelling. You may need to use a cane or crutch and wrap your knee in an elastic bandage. In rare cases, a Baker’s cyst is removed by surgery.
- Rest your knee as much as you can.
- Take over-the-counter medicines to reduce pain and swelling. These include ibuprofen (Advil, Motrin) and naproxen (Aleve).
- Use a cane, crutch, walker, or another device if you need help to get around. These can help rest your knee.
- If you wear an elastic bandage around your knee, make sure it is snug but not so tight that your leg is numb, tingles, or swells below the bandage. Loosen the bandage if it is too tight.
- Follow your doctor’s instructions about how much weight you can put on your knee.
- Stay at a healthy weight. Being overweight puts extra strain on your knee.
A popliteal cyst will not cause any long-term damage, although it can be uncomfortable and annoying. The symptoms may come and go. In most cases, the condition will improve over time or with surgery. Long-term disability due to a popliteal cyst is very rare.