I did tai chi for 14 years and still suffered three spinal fractures. If you have osteopenia or even mild osteoporosis, by all means try Fishman's yoga. Margaret Martin is another great resource. If your osteoporosis is more severe, I would be careful doing the exercises (Martin modifies yoga for those with osteoporosis and Fishman may too) and I personally would not rely on exercise to heal the bone loss.