From what I know it went from "back strain" to Gronk seeing some out of state specialist for the surgery. There were rumors it was the same guy who worked on Urlacher's neck. This stuff has all been pretty secretive, but I would say his pro do will be more telling. If he has disclosed what the surgery was somewhere, it would be news to me. But, his physical abilities and hand skills are a rare combo at TE, and I would say it is definitely a better risk to take than thinking Olsen will suddenly learn how to block.