With osteoporosis, it's important that you do weight bearing exercises, such as walking, to increase bone density. Eliptical and stationary bike are great for cardio, but not weight bearing. There are many different elipticals out there and they all feel different. I realize you want to use the eliptical or bike to recover but let's back up a bit. Chronic injuries are not normal and you need to discover what is the source of your injuries.
You have to get in contact with a doctor who understands your need, past injuries and is sport minded to know what you are going through and what you want to achieve. There are some great advice on this forum but something as severe as osteoporosis, you ought to seek MD help right away. Best of luck.