Idk about your condition but I have scoliosis im 17. I use to go to the doctor every week to get my back tweeked cuz it hurted soo much everyday. I couldnt even wash the dishes but p90x took the pain away i swear. My back never hurts anymore and I never go to the doctor i guess it was the back exercises it healed my back (:

Listen to your body. Start off easy and work harder as you gain confidence in a particular move. If something hurts (in a bad way, rather than a muscle building way) back off that particular exercise. Either modify it or skip it. There's no P90X police that I'm aware of (even though Tony MAY come to your house if you're doing it wrong )

There's enough variety in this program that you'll still get a great workout.