Greenfield filter? and why?

Can someone please tell me what is a greenfield filter? I am about ready to have my surgery and I have read numerous profiles who spoke about this filter. What is it and why do people have them put in and who needs them put in. I want to make sure that maybe I need one before surgery. Can someone please help me out on this? Thanks so much!!

My surgeon put it in. They do it in case blood clots form in your legs and break off the filter would catch them from going to your lungs or heart. I hope this helps.

Thankyou for the information. I don't think my surgeon uses them. Are they common? I am considering asking my surgeon about this. Thanks again..Dee