I've got stubborn fats in my upper and lower abdominal part. But here's the thing. My upper torso is irregurly shorter than that of my legs.. its so not in proportion! (got it from mom) so I really find it hard to do crunches, upper torso is irregularly short. I feel that my neck is doing all job whenever I do crunches which should not be the case.. I keep contracting my ab muscles but it really doesn't lift me at all! For the lower abs, leg raise freaks me out to cause I feel the scary feeling that my knees are going to be screwed, got ACL on both knees so my knee joints are floating and Orthopedic said I'll have it for life.
Suggestions please.. :(

Try hip lifts, bicycle exercise, (work your legs as if on a bike, while lying on back) ab rocker (need the equipment), exercise ball crunch, (need the exercise ball). These really are less stress on bad knees. Any resistance training, using stretch bands, they are available everywhere and are cheap. Walk if you can with weights on your ankles. Swimming also will help, no stress on joints, if ones available to you! It the best overall exercise there is!