My buddy has ankylosing spondylitis, which is basically arthritis leading to fusing of the spine. Causes him to get hunched over and painful. But with an exercise regime he has stalled it. He doesn't kite, but still surfs ... though longboard only. So if that's what you have, there's hope!
Foiling can be pretty intense in initial learning stages, unless you take it easy: start with short mast for sure, makes it so you don't wipeout when you come off foil, and even if you do wipeout, not much consequence. I am believer in starting behind boat....really slow to start, so slow you can't possibly get on foil, then gradually increase until you can just barely pop up briefly, and then steadily increase. If you take a gradual approach, it can be pretty low impact.
Bigger surf style foil will make it easy, slow cruisey. Slingshot hoverglide is a slower easy kite foil, then the H2 and H4 wings are the surf wings that also work for kiting.
For kites, any surf/wave kite is ideal, steady and predictable, sits in back of window for fun downwind foiling in swell -- you'll be stoked, feels like snowboarding in powder. Personally I am not a big fan of clouds, find them surge-y, but I had the C1 initial version and probably didn't ride them long enough to get used to it. (broke my ankle and sold it!
Anyways, bottom line ... follow the advice of your doc/physio, do those exercises religiously, and get back on the water. Movement and action will keep you going! Best wishes