Welcome Gillian,
My age - 35 - was a factor in my selection of ADR rather than fusion. Prior to my injury, I lived a very active life. My desire was to keep as much flexibility and motion as possible post-surgery; therefor, I chose ADR over fusion. The materials used in the devices is similar to artificial knees and hips which have been implanted for several decades. My view towards a possible future surgery was that I wanted the highest quality of life for as long as possible. If it meant that in 30 years I might need a fusion, so be it. However, at the rate of medical technology, by the time another surgery could possibly be needed the procedure could be quite advanced and fusion not required.
Best wishes with your journey