Ultrasound-Guided Baker’s Cyst Aspiration & Cortisone Injection

What is a Baker's cyst?

What is a Baker’s Cyst (also known as a popliteal cyst)?

A Baker’s cyst is a swelling at the back of the knee due to fluid accumulation. A Baker’s cyst Knee can be an isolated problem, but usually, it is associated with a build-up of excess fluid within the knee joint itself (referred to as knee joint effusion), as some of the fluid may be pushed to the back of the knee. A Baker’s cyst in the knee is usually secondary to a knee joint condition that results in a build-up of fluid, such as knee joint inflammation (for example, in Rheumatoid arthritis), knee joint wear and tear (osteoarthritis), and meniscal and cartilage tears. Baker’s cysts are benign (not aggressive or malignant) but can be large and painful, causing pressure and discomfort at the back of the knee.

Other conditions that can be seen in association with a Baker’s Cyst are:

Cartilage (meniscal) tear
Knee joint osteoarthritis
Patellofemoral joint osteoarthritis (knee cap pain)

What are the symptoms of a Baker’s cyst?

The main symptom is swelling at the back of the knee. Patients usually describe a feeling of pressure or pain at the back of the knee, and sometimes they can feel or see a lump on the back of the knee. The swelling can vary over time and change in size daily.

If large enough, it can lead to pain and restriction of movement, particularly when straightening the knee.
A Baker’s cyst can sometimes leak (usually referred to as a ruptured Baker’s cyst). This can present with sudden pain, swelling and bruising in the calf. If these symptoms occur, it is important to see a doctor to rule out a more serious condition called deep vein thrombosis or “DVT”, which refers to a clot within the deep veins in the leg.
Other symptoms may include knee joint pain and locking (occasionally due to other conditions associated with the Baker’s cyst, like meniscal/cartilage damage within the knee)

What are the causes of Baker’s cyst?

The synovial fluid keeps the knee joint lubricated, allowing the knee to move freely without friction between the bones. However, excessive fluid accumulation can lead to joint effusion and Baker’s cyst formation.

Baker’s Cyst can happen due to:

An inflamed knee joint, which can be brought on by different forms of arthritis, most commonly, osteoarthritis, gout and rheumatoid arthritis.
A cartilage tear or other kind of knee injur, for example meniscal tears.
A Baker’s Cyst can develop in any person, especially if there are pre-existing injuries or arthritis in the knee joints, including the knee cap (patellofemoral) joint.

What are the complications of Baker’s Cyst?

Rupture is the main potential complication of a Baker’s Cyst. This can happen particularly in large cysts. A burst Baker’s cyst has the following symptoms:

Swollen of lower leg/calf
Sharp and stabbing pain in lower leg/calf

How do I know if I have a Baker’s cyst?

If you have the symptoms described above, you may have a Baker’s cyst. Please see your doctor to examine you and rule out other causes of knee pain. Your doctor will usually ask for an ultrasound scan to confirm the diagnosis.

What is the best type of scan to assess for Baker's cyst?

Ultrasound examination is very useful in confirming the diagnosis of a Baker’s cyst. MRI examination is also useful to assess the knee joint in general as well as the Baker’s cyst. In addition, imaging will differentiate the Baker’s cyst from other conditions that can cause swelling at the back of the knee (like a soft tissue tumour) or enlargement of the artery at the back of the knee, “popliteal aneurysm”.

How long does it take a Baker’s cyst to heal?

Unfortunately, a Baker’s cyst can carry on for an extended period, especially when it is secondary to an underlying knee problem (like osteoarthritis or ligament damage). If a Baker’s cyst ruptures, it will lead to calf pain, swelling and bruising, but the cyst may reduce in size afterwards.

How do you treat Baker’s cyst?

Treatment of Baker’s cyst in the knee is only sometimes required, especially if the cyst is small in size and not causing you problems. Small baker’s cysts are often seen incidentally on knee ultrasound and MRI scans without causing pain or symptoms to the patient. However, treatment is recommended if they are painful or significantly reduce a person’s function or interfere with daily activities.

Treatment include:

RICE (Rest, Ice, Compression, Elevation)
Avoiding activities that increase discomfort.
Physical therapy to strengthen the knee muscles.
Knee surgery is only preserved if conventional management options don’t provide relief and the cyst is sizeable.
Ultrasound-guided cortisone injections

Ultrasound-guided Baker’s cyst aspiration and steroid injection

If the cyst is large and causing significant symptoms, ultrasound-guided Baker’s cyst aspiration can be performed. At the musculoskeletal ultrasound & and Baker’s cyst Injection clinic, we will perform an initial knee ultrasound assessment to establish the diagnosis and rule out other possible causes of pain and swelling at the back of the knee. Once we have a definite diagnosis of a Baker’s cyst, and if it is painful and large, it can be aspirated (the fluid is drained from the cyst under ultrasound guidance). We also usually inject a mix of steroids and local anaesthetic (numbing medicine) to settle the cyst and to reduce the pain and inflammation in the knee at the same time of aspiration.
It is important to highlight that the cyst is usually connected to the knee joint. Therefore there is a possibility of recurrence, especially if there is a generalised build-up of fluid in the joint and an underlying cause for this within the knee (for example, knee osteoarthritis or meniscal tear). An ultrasound-guided steroid injection to the cyst at the time of the aspiration would help to reduce the chance of cyst recurrence.

How is Baker’s cyst aspiration done?

Your doctor will speak to you on the day about the procedure and address your questions. The procedure is done under ultrasound guidance, and you will usually be asked to lie on your tummy on the examination table. First, the doctor will assess the area using ultrasound to determine the best approach. Then the skin will be cleaned and prepared at the site of the injection, and numbing medication can be administered to the skin using a small needle. Then, a needle will be advanced into the cyst under ultrasound guidance to allow for Baker’s cyst aspiration and steroid injection.

What happens after the procedure?

A small plaster is usually applied to the site of the procedure. You can remove this later during the same day. You can eat and drink normally before and after the procedure. You can shower as usual but avoid very hot showers/steam rooms. You can use simple painkillers like paracetamol if you experience pain at the site of the injection. It’s advised not to drive immediately after the procedure. Rest the area and avoid extraneous activities for at least 48 hours after the procedure.

What are the possible complications of Baker’s cyst aspiration/steroid injection?

The complications of a Baker's cyst injection are very rare in general. They are similar to having a steroid injection to the knee joint. These include:

Pain and discomfort for a few days. This is sometimes referred to as a steroid flare.
Temporary bruising due to small blood collection under the skin at the injection site.
Infection. This is very rare but important to be aware of.
Patients need to be aware of the possibility of Baker’s cyst recurrence after the procedure. A steroid injection would reduce the chance of this.
Patients need to be aware that Baker’s cysts sometimes contain thick fluid that can be difficult to aspirate using a needle.
If you have diabetes, your blood sugar level may temporarily increase.

How long does Baker’s cyst aspiration procedure take?

The procedure length depends on the case's difficulty and the doctor's experience. Usually, 30 minutes is a reasonable time for the whole procedure (including an explanation to the patient and preparation).

Ultrasound guided Baker's cyst aspiration and steroid injection

Do I need to perform a Baker’s cyst drainage?

If you undergo a Baker’s cyst drainage, it usually comes back, so the answer is usually no. Drainage is usually considered if the cyst is causing pain or discomfort at the back of the knee or for cosmetic reasons. A steroid injection usually helps reduce joint swelling and the possibility of recurrence.

Should I have a steroid injection into the knee joint if a Baker’s cyst is drained?

This is usually recommended. Often, the cause of a Baker’s cyst is an excess fluid produced by the knee joint itself. Therefore, it is very reasonable to attempt to reduce the inflammation and fluid production in the knee joint, to reduce the possibility of recurrence.

What are the other treatment options for Baker’s cyst?

Treatment for Baker’s cyst in the knee depends on the cause. The majority of cases are managed non-surgically. However, Baker’s cysts can reoccur even after surgical removal.

The treatment options include:

Applying ice to the swollen cyst and knee joint

Using anti-inflammatory tablets

Compression of the back of the knee using a compression bandage. You should not use this without a doctor's advice, especially if you have leg circulation problems.

Drainage of the cyst under ultrasound guidance, as we mentioned above.

Treating the underlying cause within the knee joint.

Bakers cyst vs ganglion cyst: What is the difference?

A ganglion cyst (or a meniscal cyst) results from a meniscal tear. These cysts form on the inside or the outside of the knee. Occasionally, these cysts can develop at the back of the knee and, therefore, can simulate a Bakers cyst. Generally, an ultrasound is helpful to determine whether the swelling at the back of the knee is a Bakers cyst or a meniscal cyst.

Can a Baker’s cyst cause calf pain?

Generally, a Baker’s cyst does not cause calf pain. But, if the cyst is large, it can cause pressure upon the adjacent structures like muscles, tendons, and nerves, causing pain at the back of the knee or calf.

However, it is unusual for even a large Baker’s cyst to cause severe pain. Generally, an ultrasound or MRI scan is usually recommended to confirm the diagnosis and rule out other causes of pain, such as a tumour or blood vessel enlargement (called a popliteal aneurysm). Ultrasound is usually excellent for the assessment of a suspected Baker’s cyst. A sudden onset of pain at the back of the knee or calf in patients with a Baker’s cyst can indicate fluid leakage (usually called a ruptured Baker’s cyst). The leaking fluid can irritate the soft tissue and calf muscles, causing a sudden onset of significant pain, swelling and bruising. If these symptoms occur, it is important to see a doctor to rule out a more serious condition called deep vein thrombosis or “DVT”, which refers to a clot within the deep veins in the leg. A ruptured Baker’s cyst is harmless, and the treatment usually consists of leg elevation and compression of the calf. Still, it must be differentiated from deep vein thrombosis (DVT), a serious condition. Ultrasound is usually excellent in differentiating the two conditions.