The decision by 3B Orthopaedics to move from Center City's Pennsylvania Hospital and become employees of Aria Health, effective Tuesday, shows that even prominent doctors are not immune from the economic forces reshaping medicine.

Driving the move was 3B's desire to expand its footprint in the region, according to Robert E. Booth Jr., one of the partners in 3B, short for Booth Bartolozzi Balderston Orthopaedics. The group had been an independent practice at Pennsylvania Hospital, part of the University of Pennsylvania Health System, since 1998.

"Without growth it's not going to be possible in the contemporary world to continue practicing," Booth said. "The economic pressures are pretty obvious. Everyone is reimbursing less every year," he said, referring to payments from government and private insurers.

In becoming employees of Aria, Booth and his partners are joining a steady stream of doctors who are giving up independence to become employees of hospitals or health systems.

Neither Kathleen Kinslow, chief executive of Aria, nor Booth would disclose the lengths of the employment contracts for the 3B partners, who initiated the talks with Aria, according to Kinslow.

Kinslow, who was executive director of Pennsylvania Hospital before taking over at Aria two years ago, said Aria had been thinking about expanding orthopedics. "We are a community hospital and we want to make sure we are meeting the needs of our community," she said.

Aria now performs 2,500 inpatient and outpatient orthopedic cases annually. With 3B, that figure is expected to reach 6,000.

The eight 3B partners are getting far more than jobs at Aria, which has hospitals in Philadelphia's Frankford and Torresdale sections and in Langhorne, 3B's new home base for joint replacements and other services.

In connection with the move, Aria created the Aria 3B Orthopaedic Institute, with 50,000 square feet of office space, eight operating rooms, and 30 private inpatient rooms.

"It may be situated in a community, but it's essentially an orthopedic-oriented hospital," Booth said.

Aria 3B will keep its Cherry Hill office and open one in the Curtis Center in Center City. Aria 3B will employ 145, in addition to the doctors.

Among Aria 3B's competitors in Bucks County is the Rothman Specialty Hospital in Bensalem, which opened last year with six operating rooms and 24 inpatient beds.

Alan Zuckerman, president of Health Strategies & Solutions Inc. in Philadelphia, said adding 3B is great for Aria. "There will be people who will go see the 3Bs at Aria who never would have gone to Aria, and will stay," Zuckerman said.

As for Pennsylvania Hospital, Penn Medicine spokeswoman Susan Phillips said: "We have a strong orthopedics program across Penn Medicine and the departure of one set of physicians will not have a lasting impact."