Baker's Cyst

Q:  I have swelling on the inside of my knees with a lot of pain behind the knees. My doctor told me it was a "Baker's cyst." Can you please tell me how I got this and how it can be treated? Thank you and may you have a nice forever.

A:  Baker's cysts, which are a swelling behind the knee, located right in the bend area above the calf, are not that uncommon. Before explaining how you got this, I need to give you a quick anatomy lesson.

A bursa is a small pouch or sac found where tendons attach to bones. Behind the knee there is a bursa between the calf muscle and the knee joint. In about 40% of people there is a natural communication or pathway between the bursa and the knee joint. This means that if you have rheumatoid arthritis or osteoarthritis or other knee problem which causes swelling and inflammation in the front of the knee joint, this fluid can build up pressure and flow into the bursa behind the knee creating a cyst (a fluid-filled sac).

Early on, there may be some slight puffiness noted behind the knee while standing and just a little discomfort. As more fluid accumulates, more pain will be noticed, especially when bending the knee or straightening it very tightly. Sometimes the fluid will extend down into the calf muscle or the cyst can actually rupture causing acute swelling and pain of the lower leg which can mimic phlebitis (a blood clot).

An ultrasound test can be done on the area to diagnose and monitor a Baker's cyst. Treatment involves injecting a corticosteroid into the knee joint or cyst. Sometimes an operation may be necessary if the problem really stems from the knee joint.

Thank you for your good wishes. I hope you have a nice forever, too! Also a better today inspite of your Baker's cysts.

"Dear Doctor" is a compilation of patient questions answered by doctors from the Medical College of Wisconsin.