I have osteopenia, too. If necessary, for severe pain that won't let up, I am allowed one or two injections a year. If you take fosomax, it would be even safer. I can't afford it, it isn't covered by Medicare Part D, so I take 1200mg of calcium daily. It must be working okay because I had a fusion in Feb and in 6 weeks both sides were almost completely fused. And 1 inj for something like the SI joint won't hurt anything.
Carol