A popliteal cyst, also known as a Baker’s cyst, is a soft, usually painless bump that develops on the back of the knee. These cysts occur most often when the knee is damaged due to arthritis, or acute or chronic inflammation in the lining of the knee joint.
A popliteal cyst is a small, bag-like structure that forms when the joint lining in the knee produces too much fluid. The extra fluid builds up and pushes through the back part of the joint capsule, creating a cyst. The popliteal cyst squeezes out toward the back part of the knee in the area called the popliteal fossa, the indentation felt in the back part of the knee between the two hamstring tendons.
A popliteal cyst may form after damage to the joint capsule of the knee. The weakening of the joint capsule in the damaged area of the knee can cause the small sac of fluid to form. A popliteal cyst can actually be an indicator of other conditions that cause swelling in the knee joint. This swelling is most often from problems of osteoarthritis or rheumatoid arthritis in the knee joint. It can also be caused by trauma, from a direct blow to the knee or from repetitive activities that lead to overuse in the knee joint. Trauma or repetitive activities can sometimes cause a meniscus tear which can also lead to the popliteal cyst developing in the back of the knee.
At first, your MD will ask you to describe the history of your problem. A physical exam is usually needed to diagnose a popliteal cyst. Unless the cyst has ruptured, no further testing is needed. If the cyst has ruptured, additional tests will be required. X-rays will not show the cyst since it is a soft tissue injury. A cyst can be seen with a magnetic resonance imaging (MRI) scan, or your doctor may order an ultrasound test. This is useful in determining whether the lump could actually be a tumor vs a popliteal cyst.
First, let's describe the nonsurgical treatment of a popliteal cyst. The nonsurgical treatment would be drawing the fluid out with a needle and syringe can reduce the size of the cyst. Usually, cortisone can be injected into the knee to assist with decreasing inflammation. Nonsurgical treatments also include a simple method of rest and keeping your leg elevated for a few days. In some instances, your doctor may prescribe a round of physical therapy. Common treatments may include massage, compression wraps, and electrical stimulation to reduce knee swelling. Flexibility and strengthening exercises for the lower limb may be used to help improve muscle balance in the knee.
The surgical method to remove the popliteal cyst is to repair the hole in the joint lining where the cyst has come through. Unfortunately, about half of the time the cyst comes back or recurs after being removed. Surgeons are very cautious when suggesting surgery to remove a popliteal cyst because they are most likely to recur in the future.
With nonsurgical physical therapy, a popliteal cyst may improve in two to four weeks. Progression depends on the improvement in the underlying condition that causes the swelling. Usually, it is advised to avoid activity that causes the swelling. As long as the joint continues to swell, the size of the cyst will probably grow. If the knee is kept from swelling, the cyst won’t swell/grow. In physical therapy, treatments such as ultrasound, electrical stimulation, and soft-tissue massage may be used to decrease pain and swelling from the cyst.
If you decide to have surgery to remove the cyst, you can resume your daily activities and work as soon as you are able or depending on what your doctor recommends. You should keep your knee elevated up for several days to avoid swelling and throbbing. Take all medicines exactly as prescribed or as needed per doctor recommendations. Your doctor may want you to use crutches or a cane for a few days or a few weeks. If your doctor recommends physical therapy, activities may include range of motion exercises, flexibility exercises and strength exercises.