Hello Isabel Ezrati,
The best and safest way is to work with and get advice from the doctors and physical therapists. Then be careful not to bend, compress and twist the spine; keep the hips aligned: no hip abduction/adduction past midline. Pay attention to pain: do not work through pain, back off.
Incorporate balance work to prevent falls.
Natalie aka NAPS 2 B Fit.
there was an article in the IDEA Fitness Journal on that very subject, and I hope that it will be helpful to you. https://www.ideafit.com/fitness-library/modifying-pilates-for-clients-wi….
The key to exercise with the goal of slowing bone loss or improving bone density is to create tension on the attachment sites of the muscles and ligaments. It is very similar to any exercise progression. But the degree of osteoporosis is very important. You don’t need a lot of tension to get a change in bone density. But it does need to be greater than the person is used to placing on the connective tissues of the skeletal system. And it needs to be applied regularly. You can’t exercise once a week and get more bone density. And physician clearance is absolutely necessary.
As to pilates specifically, applying tension to the musculoskeletal system from as many angle as possibe would be a goal.