The Rothman Institute will expand into the New York metro area under a deal with Northwell Health, a fast-growing nonprofit health system based on Long Island, the partners said Thursday.

Rothman chief executive Mike West said the model will be similar to what Rothman, founded in 1970 by Richard H. Rothman, has done in the Philadelphia region, where it co-brands with hospitals, such as Rothman Institute at Jefferson.

"We'll start in Manhattan, with Greenwich Village, and the Westchester area," West said. Rothman will also look at Northwell's orthopedics from an operational perspective, from pre-op to post-op, West said.

Over the next three years, West said, Rothman hopes to have several offices in the New York area, with 20 to 30 surgeons and 10 to 15 nonsurgical physicians.

That represents a significant expansion from Rothman's current base of 84 surgeons and 61 nonsurgical physicians.

The cost of the expansion will be shared by Rothman and Northwell, West said, but he declined to say how much would be invested.

Among Rothman's competitors in New York will be the Hospital for Special Surgery, whose surgeon-in-chief and medical director is Todd J. Albert, a former president of Rothman.

Northwell Health bills itself as New York state's largest health system, with 21 hospitals and 550 outpatient practices. Based in New Hyde Park, it had a total revenue of $8.7 billion in 2015, the most recent year available. The system has grown rapidly through acquisitions, including one in each of the last two years.

Closer to its Center City headquarters, Rothman has outpatient centers under development in Blue Bell and Malvern. It also has two surgery centers under development locally, one affiliated with Bryn Mawr Hospital and one with Kennedy Health System in Cherry Hill, West said.