A good low-impact way to stretch and strengthen back muscles is yoga. There are several types of yoga, some of which are much better suited for those with chronic conditions.
http://www.spine-health.com/blog/top-4-beginning-yoga-poses-scoliosis-sufferers
This website includes materials that are protected by copyright, or other proprietary rights. Transmission or reproduction of protected items beyond that allowed by fair use, as defined in the copyright laws, requires the written permission of the copyright owners.