It could cause slower healing due to poor control of vascular system feeding joints with blood flow and oxygen/nutrients. Your body needs to go through phases to create new bone and properly fuse. Has your doctor/surgeon suggested doing anything differently before and after surgery to help with healing? Do you need to restrict weight bearing activity and did they recommend physical therapy? Do you have osteoporosis? Do you have any vitamin/mineral deficiencies?

Your RA and autoimmune issues may attack your joint and disrupt the inflammation and new bone formation. What material has been used in your joints? My own bone was used for spinal fusions (they took overgrowth of bone in other locations to grind down to create a “cement “ for my joint fusions to help with my body accepting the new joint material. I have heard that those who may have had cadaver bone used have rejections and failed fusions.