A popliteal cyst, also called a Baker’s cyst, is a soft, often painless cyst on the back of the knee. A cyst is usually nothing more than a bag of fluid. These cysts occur most often when the knee is damaged due to arthritis, gout, injury, or from inflammation of the joint lining. Treatment of the cyst is most successful when the underlying cause of the cyst is also treated. Otherwise, the cyst can recur.
In rare instances, the cyst can cause pressure on blood vessels, causing swelling or other problems in the leg. A ruptured popliteal cyst can be very painful. The symptoms caused by a popliteal cyst can mimic more serious problems; therefore, careful clinical evaluation is important.
The purpose of this information is to help you understand popliteal cysts:
- the nature of the disorder and the normal anatomy of the knee
- the signs and symptoms of the disorder
- the treatments available to you now and later
- what you can expect from those treatments
- what you can expect long-term if you have this disorder
In order to understand what is happening with your knee joint, you need to understand the basics about the normal anatomy of your knee. This includes becoming familiar with the various parts of the knee. The more you know about your knee, the better you’ll be able to communicate with your doctor and healthcare team.
A joint is formed where two or more bones meet. The knee is a hinge type joint and is formed where the thighbone (femur) meets the shinbone (tibia). The thighbone is rounded on the end and rocks back and forth on the flat surface formed on the end of the shinbone. A smooth cushion of articular cartilage covers the surface ends of both of these weight-bearing bones. The articular cartilages are kept slippery by joint fluid made by the synovial membrane (joint lining). Since the cartilage is smooth and slippery, the bones move against each other easily and without pain.
In addition to bones, the knee joint also consists of “soft tissues” including ligaments, tendons, muscles and blood vessels. These soft tissues work with the bones in the following ways to provide the mechanics of the knee:
- Bones are attached (connected) to bones by ligaments
- Muscles attach bones to tendons
- Electrical impulses are sent by nerves to the muscles, which makes them contract and relax causing the joint to bend and straighten.
- Blood vessels carry needed oxygen, nutrients and fuel to the muscles to allow them to work normally and heal when injured.
A popliteal cyst forms when the joint lining produces too much joint fluid. The extra fluid leaks or pushes through the joint lining and forms a cyst. The cyst often “sticks out” on the back of the knee between two muscles.
If the cyst ruptures, it can cause pain and swelling of the calf. A ruptured popliteal cyst has symptoms similar to a much more serious problem called thrombophlebitis. Therefore, it is important to determine right away the cause of the pain and swelling in the calf.
The symptoms caused by a popliteal cyst are usually mild. You may have aching or tenderness with exercise or your knee may buckle. Sometimes, there is pain from the underlying cause of the cyst, such as arthritis, an injury, or a mechanical problem with the knee.
Along with these symptoms, you may also see or feel a bulge on the back of your knee. Anything that causes swelling of the knee and more fluid in the knee joint can make the cyst larger. It is common for a popliteal cyst to swell and shrink over time.
Sometimes a cyst will suddenly rupture, or burst underneath the skin, causing a lot of pain and swelling in the calf. The fluid inside the cyst simply leaks into the calf and is absorbed by the body.
In this case, you will no longer be able to see or feel the cyst. However, the cyst will probably return in a short time.
Your doctor will need to know the history of your problem, such as how long you have had the problem, whether it’s getting worse, and whether it has kept you from doing any daily activities, like walking, working or participating in other physical activities. Additionally, he’ll want to know what makes it better or worse and if you have any pain.
Your doctor will examine your knee and leg. He will ask you to bend and straighten your knee to see if he can feel or see the cyst. Most often, a physical exam is all that is needed to diagnose a popliteal cyst. Unless the cyst has ruptured, further testing is usually not needed.
If the cyst has ruptured, additional tests will be needed. Because x-rays show mostly bones, they will not show the cyst since it is a soft tissue. A cyst can be seen with a sonogram or arthroscopy.
There are two types of treatment for popliteal cysts: surgical and non-surgical. Whether or not the cyst has ruptured, how painful the cyst has become, or how much it interferes with the normal use of your knee will determine which is the best course of treatment for you. In adults, the treatment is most often non-surgical. If surgery is needed, it is usually done on an outpatient basis. Unless there is a lot of discomfort from the cyst, surgery is rarely indicated.
Drawing the fluid out with a needle and syringe can reduce the size of the cyst. Then, cortisone can be injected into the affected area to reduce inflammation.
Non-surgical treatment also includes rest and keeping your leg propped up for several days. If non-surgical treatment fails, then complete removal of the cyst may be needed.
Many people, once they are reassured that the cyst is not dangerous, simply ignore the problem unless it becomes very painful.
The goal of surgery is to remove the whole cyst and repair the hole in the joint lining where the cyst pushed through.
Surgery can be slow and take over an hour to complete. Surgery is usually done under a general anesthetic, where you are completely asleep during surgery. A spinal anesthesia may also be used. A “spinal” works by numbing the lower half of your body. With spinal anesthesia, you may be awake during the surgery, but you won’t be able to see the surgery.
Once the anesthesia has taken effect, your surgeon will make sure the skin of the knee is free of infection by cleaning the skin with a germ-killing solution. An incision will be made in the skin over the cyst. The cyst is located and then separated from the surrounding tissues. The area of the joint capsule where the cyst originated is identified. A synthetic patch may be sewn in place to cover the hole in the joint capsule left by the removal of the cyst. Special care is taken not to damage nearby nerves and blood vessels.
Your knee will be bandaged with a well-padded dressing and a splint for support. Your surgeon will want to check your knee within five to seven days. Stitches will be removed after 10 to 14 days. Most of your stitches will be absorbed into your body. You may have some discomfort after surgery, but you will be given pain medicine to control the discomfort.
You should keep your knee propped up for several days to limit swelling and throbbing. Keep it propped up on a stack of pillows when sleeping or sitting up. Take all medicines exactly as prescribed by your physician, and be sure to keep all follow-up appointments.
You should expect complete healing without complications in about four weeks. The most common possible complication after surgery is infection of the incision. If infection occurs, your surgeon may prescribe antibiotics to fight infection, or surgery may be needed to drain the infection. After surgery, keep 24-hour phone numbers handy. Call your surgeon’s office if you feel your knee is not healing as it should. Check your incision as instructed by your doctor. If you think you have a fever, take your temperature. If signs of infection or other complications are present, call your surgeon right away.
These are warning signs of infection or other complications:
- pain in your knee that is not relieved by your medicine
- smelly discharge coming from your incision
- red, hot swollen incision
- chills or fever over 100.4 degrees F
- you notice bright red blood coming from your incision
- side effects from your medicine
Since popliteal cysts form very near to the major nerves and blood vessels of the leg, one possible complication of surgery is that one of these nerves or vessels could be injured during the procedure. Injury to the nerves can cause numbness or weakness in the foot and lower leg. Injury to the blood vessels may require surgery to repair them. A further complication that is uncommon but possible is that another cyst can develop.
After your surgery, you can resume daily activities and work as soon as you are able. Your doctor may want you to use crutches or a cane for a time. Avoid vigorous exercise for six weeks after surgery. You should be able to resume driving two weeks after surgery. A short course of physical therapy may be indicated to help you regain the strength in your leg.
While a popliteal cyst is not a life-threatening problem, a ruptured cyst can mimic one and can be cause for concern until a diagnosis is made. It is important to know that these cysts are always limited to the knee. The cysts are not cancerous and will not become cancerous.
Removal of the entire cyst, if necessary, will usually give a very good result. The cure is often permanent, but preventing further cysts depends a great deal on the success of treating the underlying cause.