A knee cyst is a small growth filled with joint fluid that extends to the back of the knee. Also called a Baker's or popliteal cyst, it normally forms in response to arthritis or a cartilage injury. Though most are not very serious, they do sometimes cause pain, and must be diagnosed by a healthcare professional. Both non-surgical and surgical treatments can be used to address cysts, depending on their severity.
When fluid from the knee projects to its back section, called the popliteal area, a cyst results. The fluid is known as synovial fluid, a substance that lubricates parts of the joints to reduce friction and wear and tear. Inflammation of the knee, which often is associated with arthritis in older patients, can lead to too much synovial fluid. A knee injury, which may cause a tear in the cartilage, can also lead to a knee cyst, as can a tear in a ligament.
Symptoms and Diagnosis
The symptoms of a popliteal growth can vary. Some people may don't have any symptoms, while others have stiffness, swelling and knee pain that may get worse when the leg is extended or during activity. Many people have a noticeable, tender bulge that feels like a water balloon on the back of the knee. Anyone who experiences quick bruising and swelling accompanied by pain in the knee should seek professional care immediately, because these symptoms are often associated with blood clots.
When diagnosing a knee cyst, healthcare professionals first conduct a physical exam. They check the back of the knee for growths, and evaluate the person's range of motion with the affected leg. To see if the cartilage in the knee is torn, a healthcare professional can use a procedure known as transillumination to pass light through the cyst to look for fluid. Magnetic Resonance Imaging (MRI) scans can also help determine if the growth might be a tumor, especially if the person has a fever. X-rays might be required to determine if the cyst is associated with arthritis.
Cysts that cause pain and limited mobility are usually treated non-surgically first. Healthcare professionals usually inject a corticosteroid into the knee to relieve pain. After this, a person with a knee cyst needs to rest as much as possible, apply ice to the area and wrap the knee in bandages. Physical therapy can help improve range of motion. Large growths can be aspirated, or drained with a needle. In some cases, a knee cyst will burst on its own, causing bruising, swelling, and pain. Though this is unpleasant, it usually doesn't require any treatment aside from painkillers, as the body will absorb the fluids in a matter of weeks.
If the growth is not painful or interfering with activities, it may not require treatment at all. These growths often dissipate over time on their own, although this can take months or years. If a healthcare professional decides to hold off on treatment, he or she may advise a person to wear an elastic knee bandage to support the knee.
An individual who has torn cartilage may undergo surgery to fix or remove this damaged area of the knee. When surgically treating a knee cyst, the health care professional aims to eradicate the swollen tissue that contributes to the formation of the growth. If no other treatments work, then he or she can remove the fluid-filled sac as a final resort. Most healthcare professionals try to avoid this, however, as there is a risk of damaging the surrounding tissues, nerves, and blood vessels in the knee.
A person who is susceptible to developing knee cysts should avoid performing exercises that are hard on the knees or legs. Diets that are low in sodium further reduce inflammation, which can cause cysts. In addition, an individual might need to lose weight to prevent putting too much strain on the knee joint.