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Baker's Cyst
Definition:
A Baker’s cyst is an accumulation of synovial fluid behind the knee. It is also known as a popliteal cyst because it appears in the popliteal area at the back of the knee. It is a fairly common, benign condition; it is not a tumor and will not spread into other areas of the body.
Synovial fluid is a slippery substance that lubricates and nourishes the articulating surfaces of the knee joint. It moves between pockets in the joint known as bursae, and is normally contained within the tough tissues of the joint capsule. If the joint becomes inflamed, one response of the body is to produce more synovial fluid. Occasionally, body weight compressing the fluid within the joint forces some of it to burst through the joint capsule where it collects in a bursa in the popliteal area behind the knee.
Causes:
Overproduction of synovial fluid, caused by inflammation of the knee joint, causes a Baker’s cyst. The reasons that such inflammation might occur are:
- A tear in the meniscal cartilage (a pad of cartilage between the articulating bones), or another ligament in the knee
- Osteoarthritis: this is the most common form of arthritis to cause a cyst
- Rheumatoid arthritis
- Juvenile arthritis
- Some other injury causing swelling in the knee joint
Symptoms:
Often there are no symptoms at all. If symptoms exist they may include:
- A soft swelling behind the knee, which might or might not be tender to the touch
- The back of the knee may feel tight
- The swelling can feel like a balloon filled with water
- Any pain may be worse when the knee is fully stretched or bent, or when the leg is active
- Symptoms can be constant or intermittent
- Rarely, the cyst may rupture. In this instance there might be pain and rapid swelling with bruising at the back of the knee and calf. There may also be a feeling that water is running down the calf.
If the symptoms of pain with rapid swelling and bruising occur, seek medical assistance immediately as such symptoms are very similar to those caused by a blood clot, which can be a very serious condition.
Diagnosis:
Your doctor will ask detailed questions relating to the onset and severity of the symptoms; whether any pain or stiffness is constant or comes and goes; whether your knee locks or feels unstable, and what, if anything, makes the symptoms better or worse.
You will also have a careful physical examination to view any mass, if present. You may be asked to perform certain exercises to assess range of motion of the knee. The doctor will look for possible signs of a tear to the meniscal cartilage. Transillumination, or the passing of light through the cyst, will reveal if the cyst is fluid-filled or solid.
Imaging tests such as x-ray, ultrasound or MRI (magnetic resonance imaging) might be used to look for any damage to the bones or surrounding tissues. Sometimes your doctor might use contrast dye injected into the joint, a test known as an arthrogram, to help with a diagnosis.
Treatment:
Often, the best course of treatment is observation as a Baker’s cyst can go away by itself.
If pain is being experienced, the treatment usually consists of resolving the problem that is causing the cyst. The cyst itself is often not removed as it can return later and surgery might cause damage to nearby blood vessels or nerves.
Self-help options:
- Rest the knee by avoiding activities or movement that make the symptoms worse
- Wear a knee sleeve or brace
- Apply ice, crushed and wrapped in a towel, to the knee to reduce swelling
- Elevate the knee above the level of the heart, when possible, to reduce swelling
- Take over the counter medications such as acetaminophen (Tylenol), ibuprofen (Advil), naproxen (Aleve) or aspirin to relieve pain and reduce inflammation
Needle aspiration of the cyst is a procedure often used to treat a Baker’s cyst. The needle is inserted into the cyst and the fluid drained off. This is very successful at relieving symptoms, but does not guarantee that the cyst will not reform. Your doctor might inject the area with a corticosteroid at the same time, to reduce inflammation.
If the cyst is large enough to restrict normal movement, and is causing pain, surgery may be performed to repair or remove any torn cartilage in the knee joint. The cyst itself might be removed if other treatment has failed to resolve the problem.
Physiotherapy can include icing the knee, placing a wrap around the joint and using crutches to minimize weight being put on the leg. You might be instructed in how to perform certain exercises to increase the range of motion of the knee.
Exercises:
Be guided by your doctor or physiotherapist as to how much and what exercise you should do.
Back of knee stretch:
Standing up, place the ball of one foot on a step in front of you. Keeping the knees and back straight, lean forward as though to touch your toes. Hold the stretch for 20 seconds then stand up again. Switch legs and repeat the exercise.
Straight leg raise:
Attach light ankle weights to your ankles, not heavier than 1 pound. Sit on a chair with one leg straight out in front of you and resting on the seat of another chair. Keep the leg straight as you lift it up a few inches off the chair. Hold for 10 seconds then return the foot to the chair. Rest for 10 seconds and repeat. Do this for up to 3 minutes. Switch legs and repeat the exercise.
Knee wrap or brace:
Wearing a brace or wrap on the knee will provide support and restrict movement of the joint to aid healing, especially if surgery has been performed. The brace or wrap should feel comfortably tight when on the knee, but not so tight as to cause any tingling sensation, or swelling or numbness of the leg below the knee.
Prevention:
- If you are prone to developing these cysts, take care not to overdo exercises that stretch the hamstrings, which are the muscles in the back of the thigh.
- Maintain a healthy weight: being overweight places stress on the knee joint, which can lead to arthritis, one of the causes of Baker’s cysts.
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