Bankrupt hospital operator Steward Health Care received a bankruptcy judge’s approval on Friday to sell its nationwide physician network to a private equity buyer while its stalled efforts to sell Massachusetts hospitals caused the state to step in and seize one hospital. U.S. Bankruptcy Judge Christopher Lopez on Friday approved a $245 million sale of physician network Stewardship Health to Rural Healthcare Group, a Kinderhook Industries-owned network of primary care providers that operates in Tennessee and North Carolina.