Baby boomers are living longer, getting their aching hips and knees replaced as they age. That puts Illinois Bone & Joint Institute in the sweet spot of medicine.

Hip and knee replacements are among the most common surgeries in the U.S.—and they're pricey. Everything involved in replacing one, from surgery to the weeks of rehab that follow, costs an average $36,000, according to Guroo, a site created by the nonprofit Health Care Cost Institute that analyzes private insurers' claims. Private and public insurers, from Blue Cross & Blue Shield of Illinois to the federal government, want these procedures to cost less while improving patients' health.

IBJI has a cost-efficient recipe, one that's helped the physicians group snag national attention. It involves analyzing lots of data to ​ predict who will do well and who won't after surgery, then zeroing in on potential problem patients to prevent a poor outcome.

"It took us until the last 10 years to really start thinking, not how can we do things better, but how can we do things differently and better," says Dr. William Robb, IBJI's chief medical officer. "It didn't come easily."