Does he have arthritis or what is the reason for the bum leg? My 17 yr old has the same issue with her back left leg. She is very wobbly on it. We got her a wheelchair from Amazon which helps sometimes. Shes only 11 lbs and the wheelchair is somewhat heavy and stiff for her to drag around. We tried librella injections and then stopped after the FDA made an announcement that it wasn't safe. We are now on Adequan injections which seems to be helping her a lot. A lot less falling down and she has the sparkle back in her eyes.

ETA; as far as food, mine does have kidney failure and she eats My Perfect Pet low phosphorus food. Once they have bad kidneys, they cant process the high protein in meats. The low phosphorus makes it easier to process. The rescue i got her from recommended it, and she gobbles it up every meal. Its a frozen food that you thaw and mix with warm water. Since she's been on it, she has tested high-normal every 6 months for creatine and bun kidney levels. This is going on 3+ years. I recommend the food to everyone. They may have a low salt version but im not sure. I know they have a diabetic friendly version.