Those that have successfully rehabbed a hind proximal suspensory injury, did you do any extra maintenance to give them the best chance of staying sound the rest of their career? Any exercises, supplements, therapies, poultices, etc before or after they run? I want to give my gelding the best chance to stay sound and compete.

Also - did you experience them being weaker or stiffer on the same side of their injury? I have been experiencing that during and after he has been rehabbed and is in shape. He has been cleared several times by my vet and is chiro'd regularly but I am extra paranoid.

As far as supplements / therapies , I always laser them every day foe the first 2 mo, then 3 times per week after that . 
after they're healed , confirmed by u/s xrays of back feet to make sure we've got positive plantar angle, adjust if needed. Always shoe with a heel extension. 
Normal leg therapy , ice, PEMF, after a run. 

if your horse doesn't feel right on that side he's either not healed , has scar tissue causing pain or you've got sore stifles. 

I make sure the shoeing is right and they dont have a negative PA. Other than that, to me, the best thing you can do is regular consistent exercise. PSD, and most soft tissue injuries honestly, are the cumulation of chronic repetitive stress, not usually one acute catastrophe (although usually there is a straw that breaks the camels back event, or eventually a point in time where the lameness is enough to show itself). So to me, the controlled exercise and rehab and then continued regimented exercise is the best thing you can do for it.  

If you have access to a regenerative laser, like a vet quality, class IV modified surgical laser (Sound Smart RLT laser is the one I use) I would consider that. It's a badass machine. 

When mine have come back, i havent noticed any residual weakness or stiffness.  Do keep in mind, ultrasonographically, a PSD injury will likely never look normal again.. so dont get hung up on it trying to look like it was never injured before.  

I do like runners relief and clay poultices.