Why Are Surgical Clips Left In The Body After A Hip Surgery?

i am just curious as to why doctors leave surgical clips in and if they would be the reason that I am having so much pain in those areas, I have had two hip surgeries one from a motorcycle accident where they put rods and screws in, and I developed a nonunion, a year later I got a fee fibula graft, where right after the surgery the ankle of the area where they removed the tibula has been swollen black and blue and in extremely bad pain. Ive been to the doctor several time podiarits etc. they are diagnosing me as chronic pain, but I just found out at the ER i have surgical clips in both areas numerous surgical clips, my hip is always in pain and so is my ankle I cannot stand on it for long periods of time and this has been going on since 08/2014 and my second hip surgery was oct 2015