A Baker's cyst, also known as a popliteal cyst, is a fluid-filled sac that develops behind the knee joint. It is caused by an excess of synovial fluid, the fluid that lubricates a normal knee joint. This excess fluid can build up and form a cyst when there is an underlying problem with the knee joint, such as arthritis or a cartilage tear. The pressure of the increased fluid in the knee joint can force the lining of the joint (the synovium) to herniate through the soft tissues in the back of the knee leading to the formation of the cyst.
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Baker's cysts are most common in adults over the age of 40, but they can occur at any age. They are more common in people who have arthritis, cartilage tears, or meniscus tears. Women are also more likely to develop Baker's cysts than men.
The main symptom of a Baker's cyst is a painless swelling in the back of the knee. The swelling may be soft or firm, and it may be tender to the touch. In some cases, the cyst may be large enough to cause pain and stiffness in the knee, resulting in discomfort when the knee is bent and sometimes causing restriction of bending due to its size. Other symptoms of a Baker's cyst may include:
Pain in the calf
Limited range of motion in the knee
A doctor can usually diagnose a Baker's cyst by examining the knee and feeling for the cyst. They may also consider an ultrasound scan to confirm the diagnosis and rule out other causes of knee pain. On the ultrasound scan the doctor will be able to look for a fluid-filled lump or cyst, usually seen in the inner, back part of the knee.
Most Baker's cysts do not require treatment if they are not causing pain or restriction of movement and will often settle on their own. However, if the cyst is large or causing pain, treatment may be necessary. Treatment options include:
At The Joint Injection Clinic, cyst aspiration is performed after a thorough consent process, whereby the risk and benefits of the procedure are discussed in detail with your doctor. The experienced medical doctor will then place you in a lying position, face down with the back of the knee facing upwards. The skin is cleaned using a cleaning solution to ensure that the procedure is performed under sterile conditions. Under ultrasound guidance a needle is placed into the cyst and fluid is aspirated (withdrawn). Once the fluid has been removed, a small volume of steroid and local anaesthetic is injected in order to prevent immediate reaccumulation of the fluid.
The steroid injection itself is normally completed within 60-90 seconds, after which a plaster is applied and post-injection advice is given. The patient is advised to look out for any signs of infection, specifically to check whether the local area becomes red, hot, tender, swollen or if they develop a fever. If this occurs then the patient is asked to contact the clinic immediately at which time a formal reassessment will occur and if needed oral antibiotics can be prescribed. The patient is also warned that following any injection they may notice a short-term worsening or flare in their symptoms after the local anaesthetic has worn off (4-5 hours). This may last for 3-5 days and the patient is advised to consider icing of the area using an ice pack for 10-15 minutes every hour as required.
If you experience any of the symptoms of a Baker's cyst, it is important to see a doctor to get a diagnosis and discuss treatment options. Early intervention can help prevent the cyst from becoming larger or causing more pain.
