Fragments of bone and cartilage arced across the operating room as Dr. R. Michael Meneghini drilled into the knee of his first patient at a hospital here at dawn. Within an hour, the 66-year-old woman had a replacement joint made of titanium and cobalt chrome, and she was sent home the next day.

But the Obama administration was watching over her caregivers’ shoulders. If, over three months, her medical costs exceeded a target amount set by President Obama’s health regulators in Washington, Dr. Meneghini’s employer, Indiana University Health, stood to lose money.

Such efforts to squeeze spending out of the nation’s health system may well remain as Mr. Obama exits the West Wing and Donald J. Trump takes his seat in the Oval Office. The Affordable Care Act is in extreme peril, and Mr. Obama will meet with congressional Democrats at the Capitol on Wednesday to try to devise a strategy that can stave off the quick-strike repeal of the health law that Republicans plan for the opening months of the Trump administration.

But the transformation of American health care that has occurred over the last eight years — touching every aspect of the system, down to a knee replacement in the nation’s heartland — has a momentum that could prove impossible to stop.

Expanding insurance coverage to more than 20 million Americans is among Mr. Obama’s proudest accomplishments, but the changes he has pushed go deeper. They have had an impact on every level of care — from what happens during checkups and surgery to how doctors and hospitals are paid, how their results are measured and how they work together.

“From the moment I first set foot in the Oval Office in February 2009, the president told me that the law can’t be just about covering the uninsured, but that it also has to be about changing the way care is delivered,” said Nancy-Ann DeParle, who as a White House aide helped lead the effort to pass and carry out the health law. His message, she said: “I don’t want to cover everyone and just put them in the same creaky old delivery system.”

Changes in the delivery system already affect far more people than the law’s higher-profile coverage gains. To visit IU Health, the largest health care provider in Indiana, with 15 hospitals and 8,700 doctors, is to see those changes up close. Its leaders have started moving away from fee-for-service medicine, where every procedure, examination and prescription fetches a price. The emphasis now is on preventive care, on taking responsibility for the health of patients not only in the hospital, but also in the community.