Riding after a year's hiatus

Hi: I bought a well trained 6 year-old Paso Fino gelding just a year ago. His delivary at the boarding facility coincided with my injuring my knee. It took over a year for the doctors to decide the risk was ok to put in a total knee replacement. I have visited the horse on a regular basis and done some (simple) ground work. What would you recommend I do to prepare my womderful Cayo for riding, esp trail riding again? I want to make his return to work and my first rides a possitive experience. Thank You in Advance; Pasorider