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Why Is There Swelling Behind Your Knee?

Swelling behind the knee? Pain behind the knee? What's going on?

When most people see swelling or bulging behind the knee they think of a Baker’s cyst. Typically caused when excess joint fluid is pushed into small sacs behind the knee causing the aesthetically displeasing bulge/swelling.  This issue is usually caused by rheumatoid arthritis or osteoarthritis of the knee.

BUT WAIT…this may not be your issue!

The popliteus muscle is a small muscle at the back of the knee spanning from the femur to tibia in a diagonal direction. It is responsible for the unlocking mechanism of the knee when walking. The unwinding mechanism will occur when it pulls and rotates the tibia. The popliteus also plays a crucial role in the stability of the back of the knee.  When there is an injury or dysfunction the popliteus will contract and may go into a spasm.  This will typically present as pain behind the knee, “swelling” behind the knee and feel like a block or ball behind the knee during knee flexion. The swelling behind the knee is often mistaken and misdiagnosed as a Baker’s cyst. Generally, the referral pattern of pain from the popliteus will be over the back of the knee and upper calf.  It is important to know that popliteus injuries typically occur with gastrocnemius (calf) and/or bicep femoris (hamstring) issues as well.


Two different issues, similar symptoms, but very different treatments! Having a trained therapist stretch or release the muscle spasm, typical calf stretches, and pain free knee motions can help reduce muscle spasm in the popliteus muscle. Very important that you get properly assessed and don't jump to conclusions or self-diagnose.

Get those knees checked out! 






Popliteus muscle behind the knee

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