Popliteal (baker's) Cyst

A popliteal cyst, also known as a Baker's cyst, is a fluid-filled swelling that forms a lump at the back of the knee, it often causes tightness and restricted movement. The cyst can be painful while bending or extending the knee. Conditions like a meniscus tear or osteoarthritis cause the joint to produce excess fluid, inside the knee joint which can lead to the formation of a cyst. 

Sometimes the knee produces too much of the Synovial fluid, causing an increase in the pressure forces, which create a bulge. This severe swelling causes a popliteal cyst to form behind the knee. Causes of a popliteal cyst can be:

• Injury or damage to the knee,
• Arthritis,
• Rheumatoid arthritis,
• Meniscus tear,
• Anterior cruciate ligament (ACL) tear,
• Other conditions that cause joint inflammation.

Popliteal cysts do not have symptoms and are discovered incidentally during a physical examination or on an MRI scan. When symptoms occur, they may include:

• Knee pain,
• Feeling of fullness or lump behind the knee,
• Tightness or stiffness at the back of the knee,
• Swelling in the knee,
• Bruising on the knee and calf,
• Limited range of motion.

In case of a very large cyst, it can interfere with blood flow in the veins of the leg, which can result in pain, swelling, weakness, or numbness if there is nerve compression. In severe cases, the cyst may resemble a blood clot or deep vein thrombosis, a much more serious problem.

Pathology

The Popliteal cyst is a benign swelling of the semimembranosus bursa found behind the knee joint. It is not a true cyst, as there is open communication with the synovial sac. The cyst arises between the tendons of the medial head of the gastrocnemius and the semimembranosus muscles, present posterior to the medial femoral condyle. The synovial sac of the knee joint in certain conditions produce a posterior bulge, into the popliteal space. When this bulge becomes large, it becomes palpable and cystic.

Physical examination:

The patient is asked about their medical history and previous knee injury. The patient is asked to describe symptoms. Then a physical examination of the affected knee is done and compared to the normal knee. The patient is examined for swelling, joint instability, clicking or popping noise when the knee is bent, joint stiffness and limited range of motion, etc. Palpation of the back of the knee is done where the cyst is located. Often, a cyst becomes firm when the knee is fully extended and soft when the knee is bent.

X-rays:

X-rays help to provide images of dense structures, such as bone. Although the cyst cannot be seen on an x-ray, the doctor can check for narrowing of the joint space and other signs of arthritis in the joint.

Ultrasound:

An ultrasound test uses sound waves to create images of structures inside the body. An ultrasound helps to look for the lump behind the knee and check whether it is solid or filled with fluid.

Magnetic resonance imaging (MRI) scans:

Magnetic resonance imaging (MRI), is done to produce clear pictures of the body's soft tissues. MRI scan shows an area of fluid behind the knee and the location of a popliteal cyst.

Medication: Nonsteroidal anti-inflammatory, Steroid injection, etc.

Note: Medication should not be taken without the doctor's prescription.

 Aspiration:

In this procedure, the area around the cyst is made numb, and then a needle is used to drain the excess fluid from the joint. Aspiration is often done by using ultrasound to guide the placement of the needle.

Surgery

Surgical treatment for a popliteal cyst is rarely required, surgery is recommended if the symptoms are not relieved with conservative treatment or if the cyst returns repeatedly after aspiration.

Arthroscopy:

In this procedure, a tiny incision is made under anesthesia, then a small camera is inserted called an arthroscope into the knee joint. The camera shows images on a video screen, and these images are used for surgery.

Excision:

Excision is done in case of a large cyst or in case of nerve and vascular problems, open surgical procedure is carried, to remove the entire cyst.

Immobilization:

Immobilization is recommended for several weeks after surgery to immobilize the knee, this can be achieved by wearing a knee brace.

Elevation:

The limb is kept in an elevated position to drain the excess fluid.

Ice therapy:

Ice therapy for 15 minutes every 4-7 hours will reduce the inflammation. Ice is applied to decrease pain and swelling.

Ultrasound therapy:

Ultrasound therapy is used to increase circulation, drain out the toxins and thus decrease pain.

Massage therapy:

A physiotherapist uses various massage techniques to increase circulation and decrease swelling.

Transcutaneous electrical stimulations (TENS):

Transcutaneous electrical stimulations (TENS) are used to reduce knee swelling and pain.

Iontophoresis:

Iontophoresis uses mild electrical current to push anti-inflammatory medicine to the sore area. This treatment is helpful for patients who can't tolerate injections.

Kinesio taping:

Kinesio taping is done on the backside of the knee and is proven to be effective in reducing inflammation.

Foam rollers:

For tightness and soreness, a foam roller is used to assist with any myofascial symptoms.  The foam roller is not directly used behind the knee.

Range of motion exercises:

After aspiration or arthroscopic surgery, specific exercises are done to help improve range of motion, which also help to walk right after the procedure, but strenuous activity during recovery should be avoided. Range of motion exercises is done to regain full pain-free ROM. Examples of ROM exercises are heel slides by lying on the back and sliding the heel toward to regain pain-free movement, etc. 

Strengthening exercises:

Strengthening exercises like quadriceps, hamstring, and gluteus medius strengthening are essential as their weakness can lead to poor knee biomechanics and cause pain and instability.  Strengthening with weights can be limited initially to a pain-free range of motion, for this manual resistance, therabands and weight cuffs can be used.

Stretching exercises:

Stretching exercises are used to enhance the flexibility of the lower limb. Stretching of the hamstring, quadriceps, patellar ligament, and of other structures around the knee are recommended.

To prevent the recurrence of a popliteal cyst, the patient is advised to follow the recovery instructions. The patient is advised to decrease the activity and avoid high-impact activities that irritate the knee, such as jogging, aerobics, heavy lifting, climbing, and even running, this can help prevent pain and prevent reoccurrence.