I would first let the surgeon know of the lingering pain. If that's no help , I would see his primary care doctor. The primary care should treat he problem, and/or rer yor dad o someone who can help him. Good luck.
sounds like they restored his circulation to relieve pain to his leg as it was attributed to lack of arterial blood flow?
Does the incison site continue to hurt or the lower leg? it would be odd if the incision site is on his inner thigh//upper leg..to continue to hurt for this long...has the incision healed? and where was it or is it located?
what part of his L leg was hurting in the beginning before the surgery? and have they done blood flow studies to see if in fact the surgery was a success?
Welcome to the Pain Management Forum. I am glad that you found us and posted.
I see that your post begins, "Respected Doctor." Please know that this forum does not have any physicians. Our members are chronic pain patients.
It is usual and customary to harvest vessels from other parts of your body in order to perform a by-pass surgery. When they remove the vessels sutures are required. It appears in your fathers case that the site used was his leg, thus the sutures or "string" that you refer to just didn't dissolve.
His leg pain may not be directly related to the surgical procedure. Often if blood vessels are stenotic (narrowed) or occluded in one area of the body vessels in other parts of the body are also effected. Your father may be experiencing pain from poor circulation to his leg called PVD (peripheral vascular disease). This is not uncommon in diabetes and/or those ppl with hypertension(elevated blood pressure) problems. Again I am not a physician. This is just my personal opinion.
Your father may benefit from seeing a endocrinologist. At the very least he should consult with his PCP. Best of luck to you both.