I find it hard for Sakura to be unable to not heal that...
Yeaah... thanks to Evil @NF, haha.
Actually we are talking about who knows many watts of electricity hitting his arm while he is soaking wet lying in a river. Naruto frying every single nerve in his arm is entirely possible, something that might not be possible to completely heal, remember when Naruto first used the RasenShuriken, Tsunade told him if he continues to use that move the nerve damage could be bad enough that not even she could heal, Naruto at this moment is in a position that the shock to his system could do the same kind of nerve damage.