Rococo325,
NIA started as non impact aerobics, but has evolved. The movements I've seen look like good bone building for the lower spine and hips where you have the low bone scores. And unless your disc bulges are herniated this type of exercise rehydrates the discs.
The upper body movements which make the dancing more fun aren't so advantageous for bone building, but probably aggravated scar tissue around your old fracture. Still, follow-up with your oncologist to ascertain that it isn't cancer related could be wise.
That lifting can be so hard on your discs especially if you are accomplishing something (different from lifting weights where you concentrate on form. Lifting while twisting is ill advised. And it important to lift with your legs with your back in neutral.
A lidocaine patch could ease that rib. It isn't the metastatic rib?
It is so good that either you or your medical team detected the metastasis ten or eleven years after the cancer.
Often metastasis is missed after 5 years when we feel safe.