I'm fairly well beaten up with many injuries though few are tennis related but instead I carried them onto the court. The tennis injuries were from overuse rather than traumatic ones such as falls, crashes, and other unplanned violence. If you are escorted into your 50s already having a laundry list of problems it just intensifies and at least you have the mindset to cope with it though I will say that arthritis is the most mentally taxing so far. Your best bet is to find ways to manage the pain as you go along.
As for recovery, I've found with experience that strength training is the best answer to all of these. If my legs were out of use I'd focus on upper body strength by doing pushups, pull-ups, and curls or weight training. I'm stronger now in that area than I have been in decades out of necessity as arthritis takes away leg strength and flexibility.
Back injuries are debilitating and the only answer I've found is endless focus on core building. It's always about consistency in doing the needed work. As an athlete, you at least have that as a long developed skill set. Those that had fewer injuries of course are more mentally bothered by later debilitating problems. It's all about expectations. If you are just happy to be alive, breathing, and in not too much pain I'd say a little injury and recovery routine is just another speed bump.
