Years ago, I had a very big new Zealand White boy who used to love to get on the roof of his run shelter and sunbathe. But one day he laid a bit too close to the edge, and when he fell asleep, he rolled off! He landed badly and dislocated his left hip. It was VERY painful for him, and we raced him straight to the vet, securely wrapped in a blanket to keep his hip from moving. The vet managed to get it back into place, and gave him painkillers and anti-inflamatories. We were told to keep him confined to a minimum of space for three-four weeks afterwards so that he couldn't move around to much whilst it was settling. It wasn't easy, but we managed it......and he was right as rain afterwards.....it never popped out again, and didn't seem to cause him any problems at all.
Best of luck with your boy!