The answers given are all excellent. Clearance from the client’s physician and PT, and consulting with them in designing the safest and most effective program for your client is crucial.
I also was impressed with Miraslava’s thoughts and ideas regarding working with the Swiss ball. She gave some excellent exercise ideas. As long as your client’s PT approves, give it a try. I know the results for many orthopedic patients, including those with low back issues, have proved to be excellent.