Best exercise for sufferers of Facet Joint Disease

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Hi everyone, im looking for help with some exercise besides swimming that can help burn calories and tone up!
I currently walk to and from work about 40 minutes each way and all uphill on the way back !!!!
I have facet Joint disease and need to have steroid injections into my spine every 6 months, my Doctor has said No to me being able to go back to the gym, but im stuck as i loved using the elliptical trainer, but i would lose sensation in my leg while i was using it.
so any tips would be great please

THANKS