Baker’s cysts

Large Baker’s cysts feel or look like bumps or bulges at the back of the knee, especially when the leg is stretched. They are more likely to cause symptoms than small cysts do because they place more pressure on the surrounding tissue, including nerves.

If you have a Baker’s cyst, your knee might hurt. It might also feel stiff or as if there’s something inside it – both when you’re moving and when you’re not. You may not be able to move your knee properly because it feels like there’s something stopping or blocking it. Then things like standing and walking become increasingly uncomfortable, and sometimes even very painful. If you move and use the knee a lot, the swelling may get worse.

If the fluid continues to build up, the cyst can get so big that it reaches as far as the thigh or calf. That is rare, though.

Baker’s cysts tend to be caused by other problems in the knee joint. If the joint is damaged due to a chronic condition or injury, it can’t absorb shock or reduce friction properly. So the body tries to compensate by producing more synovial fluid in the joint capsule (the sac surrounding the joint). This thick, clear fluid provides the knee joints with nutrients and also keeps them lubricated. The extra fluid is pushed into the fluid-filled sac (bursa) at the back of the knee. This sac, which is connected to the space around the joint (synovial cavity), grows bigger and a Baker’s cyst develops.

Baker’s cysts in children are usually “primary Baker’s cysts,” which develop even though the knee isn’t damaged. They tend to go away on their own.

The risk of developing a Baker's cyst is greater if you have certain injuries or chronic conditions affecting the knee joint. These include:

• A damaged meniscus
• A torn anterior cruciate ligament
• Osteoarthritis of the knee
• Inflammation in the joint capsule – for instance, due to rheumatoid arthritis. Inflammation makes the membrane surrounding the joint produce more fluid.

Age is a risk factor too because chronic joint conditions are more common as you get older. The likelihood of having a previous knee injury also increases with age.

Baker’s cysts are common in people who are over 50 or have knee problems: Around 5 to 40 out of 100 people with chronic knee pain have a Baker’s cyst. They are rare in children.

If the cause of the Baker’s cyst is treated and that reduces the production of synovial fluid, the cyst will go away. But Baker’s cysts can last for years if the underlying condition is not successfully treated.

If the cause goes away on its own (for example, an acute inflammation due to osteoarthritis), the cyst can also go away without treatment.

Sometimes, a Baker’s cyst bursts (ruptures). When this happens, the fluid leaks out and spreads through the surrounding tissue, like the calf muscles. This usually causes sudden, severe pain in the knee and calf. Bruising is also possible. After that, the fluid is gradually absorbed by the body. The tissue may become inflamed when a Baker’s cyst bursts. So it’s a good idea to consult a doctor.

If the cyst puts pressure on blood vessels, fluid can build up (edema) and cause swelling in the calf. If it puts pressure on nerves, your calf muscles might go numb or feel weak. But these kinds of complications are rare.

People who are having trouble with a Baker’s cyst usually consult their family doctor first. Depending on what’s causing the cyst, they might go to an orthopedist or rheumatologist instead. The doctor will ask about any pain or impairments you're experiencing, as well as possible causes – like previous injuries or conditions such as osteoarthritis.

They’ll also take a close look at the knee joint and check for any reddening, swelling or anything unusual in the way you move and walk. If they think you might have a Baker’s cyst, they’ll do the following examination: First they will ask you to lie on your back or stomach. Then they will feel the back of your knee while you stretch and bend your leg. The cyst can be clearly seen and felt when the knee is fully stretched, but not when the knee is bent at a 45-degree angle.

Imaging techniques can be used to check for other things that could be causing the symptoms. An ultrasound scan can be done by an orthopedist. If the cause is still unclear and the symptoms don’t go away within a few weeks, an MRI scan ( magnetic resonance imaging) can help to find the cause. Patients are often referred to a radiology practice or hospital for this.

If there is red, painful swelling – especially in the calf area – an ultrasound scan will be done to rule out inflamed veins (phlebitis) or deep vein thrombosis in the lower leg. These conditions can have serious consequences and need to be treated urgently.

If you’re one of the many people who has a symptom-free Baker’s cyst, you won’t need any treatment. If you do have symptoms, they can be treated without surgery (“conservative treatment”) at first to provide relief.

Here are some of the self-help measures you can try:

• Take breaks and put your leg up after strenuous activity
• Use (support) bandages
• Apply heat or cold to the back of your knee, depending on what feels better
• Use pain-relief medication, like ointments you can make a compress with
• Do exercises to stretch and strengthen your muscles – for instance, to help your knee regenerate if you have osteoarthritis

If none of the above approaches help, it might be a good idea to see an orthopedist. They will be able to tell you about other treatment options. One possibility is to drain fluid from the knee joint or Baker’s cyst (a procedure known as needle aspiration). This involves inserting a needle into the joint or cyst and removing the fluid through the needle. The doctor also injects an inflammation-reducing drug (like steroid medication) into the joint or cyst. This approach isn’t used much nowadays, though, because the cyst can quickly fill back up with fluid again. Other treatments for underlying causes are sometimes used too. They include physical therapy for rheumatoid arthritis or osteoarthritis.

If these treatments don’t improve the symptoms, another option is to have knee surgery to treat the cause of the cyst. If the cause can't be treated surgically, it generally doesn't make sense to have surgery alone. This is because there’s a high risk the cyst will keep coming back if your body continues to produce too much synovial fluid.

Although Baker’s cysts are generally quite harmless, they're sometimes very unpleasant and restrict your movement.

Activities like walking, climbing stairs and shopping can make the symptoms worse. Various things can provide relief – including having a rest, putting your leg up or applying a cold or heat pack (depending on the underlying condition).

But it can be difficult to rest your leg every time you do something strenuous in daily life. So it makes sense to plan ahead when you’re going to be doing something strenuous, make time for breaks and set priorities. Perhaps you can do the gardening or shopping at a later date, for instance, or ask your family, friends or neighbors for help.

When people are ill or need medical advice, they usually go to see their family doctor first. In our topic "Health care in Germany" you can read about how to find the right doctor – and our list of questions can help you to prepare for your appointment.