It's my understanding that obligations you take on after your divorce - like a new invalid wife - are not a reason to reduce child support, and I would think the same should apply to alimony.
Also - I'm hard pressed to think of a disease process in which one would require SEVEN back surgeries. If she has chronic back pain after 6 surgeries, it is VERY unlikely that a seventh is going to fix anything, unless it's to insert a pump for pain medications. I'd be quite curious as to whether there is any PROOF she's had all these surgeries?