The state's most powerful health care system on Tuesday abandoned its three-year effort to acquire South Shore Hospital, the centerpiece in Partners HealthCare's controversial expansion drive, which had riveted and divided the Massachusetts medical community. Regulators are still reviewing another front in Partners' troubled expansion plans, an effort to acquire two hospitals north of Boston and a physicians group on the South Shore. The health care system said it has put on hold the plan to acquire those hospitals. The decision to retreat on South Shore Hospital, disclosed in a court document, came after a state judge in January rejected a deal Partners struck with the state's previous attorney general, Martha Coakley, to allow the acquisition to go forward.
