Gaara's the other reinforcement. Sand's out to get Sound back for the Kage-cides. Why would Kiba go "WTF, MATE, Why are they coming here? *splash into water*".

And I think yea - maybe the surgery was already done when Lee gathered the gang for the mission. Lee was just recouperating. And it makes most sense, like Khaodessy said, Tsunade could have done her Jutsu that stole your life for healing power thingy on Lee.

BOOM!