P90X Upper Body

I have been doing the X on and off for over a year now. I am having chronic knee problems and havent completed a full 90 days due to surgeries and injuries. I believe I have a solution to my problem. I will try 90 days of P90X without legs or plyo. I am starting today and substituting core synergistics for plyo and upper body plus for legs and back. My legs are already strong, the problem is my knees are damaged. Day 1 went great as usual. Stay tuned because this success story has a new begining.