Hi Alan (@alanbruce), I also have osteopenia that was recently diagnosed after a bone density scan. My PMR came out of remission after 6 years about a year ago. The first round with the PMR I was put on 20 mg prednisone and was not able to taper off until 2010. This second time with PMR I was started at 20 mg prednisone and I'm currently at 3 mg tapering off about 1 or 1/2 mg a month. My doctor suggested I add 1200 mg Calcium supplement daily and I initially didn't do it because it binds me up pretty good. I started taking the calcium again and using metamucil fiber to help with the constipation. I also started taking a Collagen Hydrolysate gelatin supplement for bones/joint care to help with the osteopenia. I would talk with my doctor about fosamax and it's safety. Fosamax has some safety concerns according to a few searches I've done. I have no medical background or training but I do try and use a natural supplement if there is one available. Here are a couple of links with additional information on fosamax:
https://www.drugwatch.com/fosamax/
https://www.health.harvard.edu/diseases-and-conditions/whats_the_story_with_fosamax
Hope this helps,
John