Updated: Jan 24
A Baker’s cyst or popliteal cyst forms in the back of the knee and gets its name from Dr. William Morrant Baker, the surgeon who first described it. In this article, we explain why treating a Baker’s cyst without addressing the cause is likely a waste of time and how to decide what treatment options may be right for you. Remember, if you need more help with an injury, you're welcome to consult one of our physios online via video call.
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What is a Baker’s cyst?
There are several tendons that cross over your knee joint on all sides. Wherever a tendon is close to a bone or another tendon, there is a bursa (a fluid-filled sac), which helps to reduce the friction and compression between the tendon and the bone or between the tendons.
The bursa in the inner corner of the back of the knee is special – it is directly connected to the knee joint via a one-way valve. The synovial fluid that lubricates and feeds the knee joint can flow through this valve into the bursa, but not out again.
What causes a Baker’s cyst?
When something in the knee joint is irritated and inflamed, it triggers an increase in synovial fluid production. Some of this extra fluid gets pushed into the bursa at the back of the knee, and as the pressure from the fluid increases, it causes the bursa to swell, forming what is known as a Baker’s cyst.
Common conditions that can cause a significant increase in fluid inside the knee joint that may induce a Baker’s cyst include:
Injuries to the cartilage
Inflammatory arthritis, e.g. rheumatoid arthritis
Baker’s cyst symptoms
Not all Baker’s cysts cause trouble – in most cases there are no symptoms. When there are symptoms, it can be any of the following.
A sensation of fullness or stiffness behind the knee.
Achiness behind the knee.
You may notice that the back of your knee looks swollen when you extend it fully.
If the Baker’s cyst is very large, it may prevent you from fully bending your knee.
It may compress the blood vessels in the back of your knee, causing your lower leg to swell, turn blue or red, and hurt a lot. These symptoms are similar to those of a blood clot (DVT), and you should consult a doctor immediately if you experience any of them.
In rare cases, the cyst may compress a nerve (tibial or peroneal) in the back of your knee, causing numbness and/or loss of strength in the muscles in your lower leg.
If a Baker’s cyst ruptures, it can cause severe pain and swelling in the calf that also resembles DVT.
How to diagnose a Baker’s cyst
Although X-rays don’t really show Baker’s cysts, they are still useful, as they can identify possible causes, e.g. joint arthritis or loose fragments of cartilage, bone, or meniscus.
Ultrasound scans can be useful to identify a cyst, but they are not so good at distinguishing Baker’s cysts from other conditions, e.g. meniscal cysts or tumours, which can look very similar. They also don’t show up other conditions, like meniscus tears, which may be the cause of the Baker’s cyst.
MRI scans are therefor seen as the gold standard for diagnosing Baker’s cysts and identifying other issues inside the knee that may have to be addressed to successfully treat the cyst.
How to treat a Baker’s cyst
To treat a Baker’s cyst, you have to understand what is causing the irritation inside your knee and take steps to address that. If you focus the treatment solely on the Baker’s cyst (like draining the excess fluid), it will likely just return.
If a Baker’s cyst is pressing on a nerve or on the blood vessels (see symptoms listed above), it is currently advised that it should be removed surgically.
All other cases are usually treated by following a three-step approach:
First, conservative treatment, which may consist of medication, ice, load management, and/or exercises.
If Step 1 does not produce good results, injections are used in combination with Step 1.
If none of the above produces good results, surgery may be an option.
Let’s look at each step in more detail.
Step 1: Conservative treatment
As mentioned earlier, a Baker’s cyst usually forms as a result of some other condition that is irritating the knee joint. The exact conservative treatment that may be right for you will very much depend on the cause.
If your doctor feels that your Baker’s cyst is in part being caused by an inflammatory condition (like arthritis), they may prescribe medication to help calm the inflammation down.
Ice can be a useful tool to reduce swelling and inflammation.
When applying ice, always place a damp cloth between your skin and the icepack (find on Amazon) to prevent the cold burning your skin. Apply the ice for no more than 10 minutes at a time, with 10-minute breaks.
Don’t use ice if you have circulatory problems or an open wound.
Load management and relative rest
An injured knee joint is usually not able to tolerate the load placed on it during your normal daily activities (standing, walking, stair climbing, running, etc.). If you continue with these, you will usually end up making things worse.
Then again, complete rest is also not useful, as it can make your knee feel even more stiff and sore. This is where relative rest comes in. With relative rest, the aim is to figure out what level of activity your knee is currently able to tolerate before it starts to feel worse. So, you remain as active as you can whilst reducing, adapting, or stopping the activities that actually make your knee worse.
Keep an eye on your symptoms for 24 hours after an activity, as things may feel fine during or immediately after the activity, only for your knee to swell or hurt significantly more several hours later. A physio can help you figure out the best combination of activities for your specific situation.
Exercises for Baker’s cysts
The exact exercises you should do when you have a Baker’s cyst will depend on what the underlying cause is and where you are in the healing process, but most patients benefit from exercises that improve circulation and strength.
Exercises that improve circulation
Ever heard the expression “motion is lotion”? Your knee joint does not have arteries or veins going into it; it relies on the changes in pressure when you move your knee to push the old synovial fluid out and to get new fluid with nutrients and oxygen. This is why keeping it super still can make your knee feel stiffer and more uncomfortable.
Low-load exercises, where you repetitively bend and straighten your knee, are brilliant for feeding the joint and getting rid of swelling. Examples include:
Bending and straightening your knee while sitting or lying down. Feel free to use your hands to help if necessary, and don’t force the movement; just take it as far as you comfortably can (see video demo).
Cycling on a stationary bike. Set the resistance to whatever is comfortable, and ensure that the seat is not too low. Your aim is to move and feed your joint, not cycle up a virtual Mont Blanc! (Cycling on the road is unpredictable; you may have to stop suddenly and might jar your knee when you place your foot hard on the road. It is also easier to control the resistance and effort on a stationary bike.)
These exercises can usually be done every day.
Running is not ideal because, although running also produces repetitive motion, it is seen as a high-load exercise and will likely irritate your knee further. You may be able to ease back into running once your knee has improved.
Strength training exercises
When we walk, our muscles are meant to absorb most of the shock and to stabilise our joints. For the knee joint, your front thigh muscles (quadriceps) are especially important. Most knee injuries or conditions like arthritis can be improved by strengthening the quads. However, you can make your symptoms worse by doing exercises that are too advanced for you, so please check with your physio before trying any exercises.
Strength training exercises that may be useful to start with:
Slow, controlled sit-to-stands from a chair (also known as box squats). Adjust the height of the chair so you can do it pain free – a higher chair is usually better.
Isometric wall sits. The more you bend your knees, the harder these are, so start with very high ones where your knees are only slightly bent.
Leg press machine in the gym. Limit the weight and how far you bend and straighten your knee to what you can do pain-free. Here’s more info on how to use the leg press for knee rehab.
Knee extension machine in the gym.
Strength training exercises should usually be done only two or three times per week and never on consecutive days, because your body needs some time to rest and recover after these sessions.
Step 2: Injections
If you’ve followed the advice in Step 1 for more than four weeks without getting results, you may benefit from a corticosteroid injection to help reduce the swelling by calming down the inflammation in your knee. Your doctor may advise that you skip Step 1 and go straight for an injection if your Baker’s cyst is very big and causes severe symptoms.
These injections can be done into the knee joint or directly into the Baker’s cyst under ultrasound guidance. In some cases, the doctor may decide to drain some fluid from the cyst before injecting the corticosteroid.
Corticosteroid injections appear to get good results but take several weeks to have an effect. It is quite normal to have a significant increase in pain the day after the injection, so ask your doctor what you should do if this happens.
Once your knee is feeling better, it is important not to ramp up your activities too quickly, especially if you’ve not done much in the weeks leading up to the injection. Your knee and muscles will need time to adjust to being more active, so it’s best to ease into being active again. You may also have to do some exercises (such as those in Step 1) to help you regain full strength and control. A physio can advise on a safe plan.
Step 3: Surgery for Baker’s cyst
Research has shown that if you remove the Baker’s cyst without doing anything about the injury or condition that caused it (e.g. meniscus tear or arthritis), it usually just ends up coming back. Therefore, surgery should rather be directed at fixing or improving whatever is causing the irritation in the knee, e.g. doing a meniscectomy or trimming frayed cartilage.
In severe cases of advanced osteoarthritis, a joint replacement may even be appropriate. Your surgeon should explain what is likely to provide the best outcomes for you.
If your Baker’s cyst is affecting the blood flow in your leg or it is pressing on a nerve, surgery may be the preferred choice of treatment, and it’s often done sooner rather than later (skipping Steps 1 and 2) to prevent complications.
Baker’s cyst recovery times
Recovery times differ widely because a Baker’s cyst can have so many different causes and vary so much in severity. Most studies that looked into the efficacy of corticosteroid injections as treatment for Baker’s cysts reported good outcomes after four to six weeks.
How we can help
Need more help with your injury? You’re welcome to consult one of the team at SIP online via video call for an assessment of your injury and a tailored treatment plan.
We're all UK Chartered Physiotherapists with Master’s Degrees related to Sports & Exercise Medicine. But at Sports Injury Physio we don't just value qualifications; all of us also have a wealth of experience working with athletes across a broad variety of sports, ranging from recreationally active people to professional athletes. You can meet the team here.