Hernia repair is fine.However honestly if it was me, I would just be up front about it.You're having a medical procedure to correct a problem with your health, and your coworkers are healthcare workers.If carol from accounting gets nosey, just offer to show her before and after photos! (But don't really, because you would totally get in trouble.)
One of my sons had to have surgical repair for penoscrotal webbing, sounds somewhat similar, and I also didnt feel comfortable blasting private details about that around casually. we made similar jokes about it being a penis reduction. But usually I just said he had a urological surgery/procedure and left it at that. If some asshole really tries to pry about details after that then they deserve the nunya response. Edited to add- he was about a year old when he had surgery, so different in that regard but still not comfortable telling people details about my babys private part situation