Casting is always uncomfortable anyway, I can't imagine having one with CRPS in that limb... I hope your wife is beginning to feel better, and well done you for caring so much that you joined this forum and asked the question she is a lucky woman!

This has probably been tried or mentioned, but have her doctors or physios tried external taping to hold the kneecap more securely? I appreciate the tape itself might aggravate the CRPS skin sensitivity where it is placed, but it is definitely covers less skin than a full leg cast! I have arthritis under my kneecap, and I know physios use taping techniques to position the kneecap so that it sits in a better position in the femoral groove. I don't know if it can help the dislocation, but you never know.

Good luck to you both.

Bram.