Poplar Bluff Regional Medical Center, which opened earlier this year, was built at a cost of $173 million by its parent, for-profit Health Management Associates Inc. of Naples, Fla. But this jewel of a hospital on the edge of a faded factory town of 17,023 residents is only one link in the health care chain's efforts to serve the region's rural population. The Affordable Care Act's success or failure will depend in large part on the efforts of rural hospitals such as Poplar Bluff to treat the poor. It may be in a shiny new building, but it has a long way to go to provide efficient, low-cost medical care in its market. And like other rural hospitals, Poplar Bluff has special challenges.