I have osteoarthritis in my spine,i have put weight on,mainly my waist,can i do sit ups to tone my stomach?

If i were you i would ask your doc first or go see a physical therapist...............you don't want to mess up your spine.......trust me, i KNOW. I have severe scoliosis so my spine is all SCREWED up...............don't take any risks w/your spine!!!!!

You need to check with a physical therapist, but having stronger abdominals is always good for back support. I would like to say it is the BEST thing for back health, but best to ask your doc!
I suggest for you to do what are called CRUNCHES (contracting the muscles in your abdomen) rather than full sit-ups with your spinal condition. - This will benefit both "sides" (front and back) by restricting your back and spine from moving and intensifying your abdominal muscles.
KEEP IT UP! - You're starting off GREAT!
Ostheo-exercising, weight training, and Aerobic conditioning.