Thanks for writing to us.
The bump that you have noticed below your knee is likely to be due to cyst- synovial or Baker's cyst or a subcutaneous swelling like lipoma
or a sebaceous cyst. A direct examination of the area is needed for proper diagnosis.
I hope this information has been both informative and helpful for you. You can consult me again directly through my profile URL http://bit.ly/Dr-Praveen-Tayal
Dr. Praveen Tayal