Definitely don't try to hide it. I have a pin in my hip and am about to finish primary flight training. I had to let the docs look at x-rays, and get an orthopedic surgeon to sign off, but no major problems. If I'd LIED about it, the best I could have hoped for was getting booted when they found out. It doesn't matter what service, officer or enlisted, they don't like to find out you lied on your application. I'm not saying you need to declare every cold you've ever had or all the headaches (hangover-induced, or otherwise) you've had, but when they can find out with one 30 second X-ray...I'd think long and hard about ommitting that detail.