I Have Had 4 Procedures, 2 On Each Knee. First

I have had 4 procedures, 2 on each knee. First I had patellar relocation surgery on both knees 40+ years ago. I had TKR on the right knee in 10-2015 and the left knee 1-2016. Rehab went well on both knees until about 3-2016 when I noticed I could no longer fully straighten my right knee. I was told I needed to strengthen the quad muscle and my pt did many different exercises and electro therapy to no avail. Then I started having my knee collapse. Now I am starting to have the same thing happen to my left knee. My OS took X-rays yesterday and told me there was evidence of Hererotopic Ossification in both knees. What can I expect. I've fallen several times, narrowly escaping serious injury. I am now back to using a walker again.