Hip joints -- and indeed other joints -- can become damaged due to
steroid use. (My steroid use came when I was on
chemotherapy for
Hodgkin's Disease.) The danger is especially great if you're a
big guy (or
big girl) -- I'm 197cm 98kg, around 6'5" 220lb.
A shorter version of the operation follows, and please note that my measurements are probably larger than usual because, well, I'm larger than usual. You get basically clamped to the operating table so you don't move during the procedure (assuming earthquakes =). You get knocked out or get an epidural. They cut an incision along your leg from a point about halfway up your bum down about sixteen inches. They then open up the incision and saw off your femur an inch or two below the ball part. If your socket has gone to crap they might remove that as well, or put a covering on it. They then drill about 9 inches down into your femur with this reaming drill that is made to make a hole just like the big spike they're about to insert in there (I got to check mine out before it went in, kewl). Then they pound that spike in there (well, gently pound). At the end of the spike is the ball part of your new hip -- in my case it was some kind of nifty space-age ceramic. Finally, they sew you up and put you in the recovery room. Then you wake up and spend a couple of days saying "ow" and pressing the button on your morphine pump.
A couple of small experiences I had that differed from the earlier noder's follow:
Sleeping on your side after a hip replacement is OK, if you put a pillow between your legs to stop them crossing or getting too close together.
I was on crutches for about 3-4 weeks, once I could get out of bed regularly. I then walked with a cane (one side was worse than the other) for another 5-6 weeks.
I've never heard of kneeling having to be avoided. I kneel just fine now (5 months after the operation), and I think I kneeled just fine after the surgery (once I could walk that is).
Sex wasn't a problem. Everything worked just fine starting about 10 days post-op. Well, post-nookie was another matter entirely as, after the Herbal Essences audition, I would suddenly become aware of a rather painful sensation in my hips, necessitating lying down and having my wife deliver me a beer and a smoke. OK, I'm lying about the beer and the smoke.
I currently walk just great, if somewhat like a penguin, but that gets better daily. I also play Dance Dance Revolution as part of my rehab.