My knees are old

Hi. I was diagnosed with sarcoidosis 19 years ago and then it was granulomas from my liver to my head and some scarring in my right lung. I felt like I had a pulled muscle back in April and I went to the sports medicine doctor thinking it was some kind of muscle issue. Mind you until then I had walked back and forth to work everyday, I was active, and I really hadn't had a lot of knee pain or issues with my knees. They did X-rays and at 47 years old both of my knees need replaced. All the tests and x-rays the doctors have done all these years and no one clocked that it would attack my knees. I'll be honest with you I didn't know it could attack my knees. Does anyone have any experience with something like that? Or some kind of joint involvement? One thing I'm wondering is is this the beginning of me needing to watch all of my other joints. What have your experiences been like?