Twenty five orthopaedic practices in the Baltimore-Washington region have joined together to form a new group, called the Centers for Advanced Orthopaedics, the doctors said Wednesday.

Together, they comprise 128 orthopaedic physicians and $150 million in annual revenue, making them the largest in the area and one of the largest around the country.

The doctors say they are bucking a health care trend by not signing on with hospitals.

The American Medical Association said a survey of doctors from 2012 showed just over half of doctors work for a practice partially or fully owned by physicians. But the number is expected to decrease -- a report the same year from Merritt Hawkins, a physician consulting firm, anticipated that by this year three-quarters of the new physician hires will by done by hospitals.

“We wanted to maintain the private practice model, still see our patients on our terms instead of introducing a new layer in between us and our patients,” said Dr. Nick Grosso, an orthopaedist at Orthopaedic Associated of Central Maryland and president of the new group. “All of a sudden there is an extra player that doesn’t benefit everybody.”

But Grosso said the doctors all believed they needed economies of scale. The doctors have already negotiated new deals for supplies and insurer reimbursement. They also have reduced their medical malpractice insurance by 30 percent, Grosso said.

All 1,200 employees now work for the new center, which now has combined billing and benefits administration. They will share best practices and clinical guidelines to improve care. But doctors' offices, however, maintain the ability to be run as their leadership wishes, Grosso said.

The venture was three years in the making and each practice put in funding to set it up. It began with Grosso’s practice and one in Hagerstown. A consultant, as well as personal relationships among the doctors, pulled in the rest.  

“We expect to continue to grow,” Grosso said. “From within and by adding new practices, if they are a good fit.”