Hello, welcome to the board!
My Surgeon used a cage on me, I was quite facinated by it - I was all ready to offer my hip for a bone graft and deal with any extra pain, but once I heard about that, I went along for it. What happens is that they use bone chips accumulated durring surgery and put that in the middle opening of the cage.. along with some things that helps stimulate bone growth if I'm not mistaken.
I'm a little over a month out of surgery now. Around 2 1/2 - 3 weeks after surgery, because of some concerns and symptoms, we had a MRI, CT, and the routine check up xray done to make sure things were good... and everything is good, in fact he said that bone growth was already taking place! I've just been having some issues with swelling and such.. which is normal after this surgery.
Good Luck to you and God Bless!