Possible spoilers if you haven't seen earlier episodes this season.
I understand that Johnny threw his cane away in order to avoid the plot trap of future Johnny but I assumed he would get a new cane.
I can buy that maybe he would suddenly realize "hey, I don't really need that cane!" but he should still have pain and some limping.
Not only does he now not have a limp but he is able to quickly run UPSTAIRS with no problem. This is just horribly lazy writing/directing/acting!
I hope it isn't a sign of where the rest of the series is going from here. I did not watch it when it originally aired.