I cam across this fascinating recent Q&A about compression fractures, which sadly are very commonly suffered by those with osteoporosis:

http://www.metrowestdailynews.com/health/x1588271712

The two things I took away from this piece are, 1) if you have osteoporosis and back pain, don't wait, hesitate or otherwise chalk it up to old age, but seek medical intervention soon -- there may be treatment options rather than living with pain; and 2) if, like me, you have various risk factors for future osteoporosis (family history, etc.) then the description of what exactly happens to your verterbrae may motivate you to renew your efforts on taking calcium and Vitamin D, doing weight-bearing exercise, and generally being conscious of your bone health to help avoid such problems in the years to come.