Do I need to worry about the mass behind my knee?

By: Dr. Zackary Byrd

The short answer is probably not. There are many things a mass behind the knee could be and rarely, some of those things are dangerous, but in the vast majority of cases it’s something much more common and benign.

Some conditions within the knee such as meniscus tears and arthritis can result in increased fluid production and inflammation, and that fluid can cause a characteristic herniation out the back of the knee that we call a popliteal cyst, or a “Baker’s Cyst.” Most Baker’s Cysts are asymptomatic but in rare cases they can cause numbness or strange sensations in the foot or even muscle cramping if it is big enough to compress the nerves or blood vessels behind the knee.

A popliteal cyst can also rupture causing warmth, redness and swelling, symptoms that resemble a blood clot. Evaluation of the cyst often involves a careful physical exam by your orthopedic provider and imaging which may be radiographs or even an MRI in some cases. Treatment of the cyst is based on treating the problem within the knee that is leading to the formation of the cyst and may vary from patient to patient depending on their diagnosis. A range of treatments exist from various non-operative therapies, drainage of the cyst and injection of a steroid, or even surgery which could be arthroscopy or even joint replacement, of course tailored to each individual and their unique situation.