Popliteal artery for a heart bypass
I'm not a physician, but I suspect the popliteal artery may not have been the vessel used.  The popliteal artery has a very important role in supplying the leg with blood, and maintaining the blood supply from it to the lower (distal) leg is sometimes reason for harvesting other vessels.
You described a very long cut, which sounds like what you would see for harvesting the great saphenous vein.  The great saphenous vein is the longest vein in the body, and dominates recent scientific publications in response to a query of ''coronary bypass harvesting''.  (There are publications in that batch evaluating newer endoscopic techniques in which the long cut can be avoided)  Wikipedia reviews the use of this vein reasonably well.