Hello, My Husband Was Diagnosed With Fibromyalgia Years Ago, He

Hello, my husband was diagnosed with fibromyalgia years ago, He had arthritis in his back from an injury then was in a car accident and had back surgery again. since then about 15years now he has been on oxycodone for the pain (chronic pain) in his legs and back. Most recently his upper back around the shoulders have been very painful he had an MRI and they said no injury just Fibromyalgia and that they see changes in the spine the formation of arthritis. He does not believe that is all it is!! now he has been having pain in his knee's mainly the right knee the back of it is all swollen puffy like it has fluid in it. I am afraid to send him back to the doctor for another MRI just to have them say it is Fibro. My question is can Fibromyalgia be causing this as well? He has had no injury to the knee . He worked construction most of his life and now works in refinery maintenance shutdowns so he walks on average 10-12 miles a day besides climbing towers.