The study will be divided into 2 phases. All study subjects will receive supplemental calcium citrate and Vitamin D during the 2-year study. In year one subjects will be randomly assigned to receive PTH (subcutaneously daily) or placebo and risedronate tablets or placebo. In year two, PTH will be stopped and subjects in group 1 will be re-randomized to receive risedronate tablets or placebo. Subjects in group 2 and 3 will continue on risedronate tablets.