They are a little-known presence in many operating rooms, offering technical expertise to surgeons installing new knees, implanting cardiac defibrillators or performing delicate spine surgery.

Often called device reps — or by the more cumbersome and less transparent moniker “health care industry representatives” — these salespeople are employed by the companies that make medical devices: Stryker, Johnson & Johnson and Medtronic, to name a few. Their presence in the OR, particularly common in orthopedics and neurosurgery, is part of the equipment packages that hospitals typically buy.

Many “people who don’t work in health care don’t realize that industry reps are sometimes in the OR,” said Josephine Wergin, a risk management analyst for the ECRI Institute, a Pennsylvania nonprofit that conducts research on medical subjects for the health care industry. “A lot of times they are the real experts on their products.”

Unlike rotating teams of nurses and surgical techs, reps are a consistent presence, experts say, often functioning as uber-assistants to surgeons with whom they cultivate close relationships and upon whom their six-figure salaries depend.

Although they don’t scrub in, reps are expected to be intimately familiar with the equipment they sell, making sure it is at the ready for the surgeon and poised to answer technical questions.

But how much influence do reps wield, how necessary and costly are their services and does their presence in the OR, which may not be disclosed to patients, raise ethical questions about informed consent?

Despite their role, device reps have received little scrutiny, in sharp contrast to drug salespeople, whose role has been the subject of considerable research.

“There’s so little public awareness of this,” said Adriane Fugh-Berman, an associate professor of pharmacology at the Georgetown University School of Medicine and director of PharmedOut, a project that focuses on prescribing and drug-marketing practices.

But the cost of medical devices, an industry with about $150 billion in annual U.S. sales, combined with concerns about conflicts of interest by doctors who must report industry payments, has resulted in increased scrutiny, as hospitals seek to standardize and circumscribe the activities of device salespeople.

Some hospitals, most notably Loma Linda University Medical Center in California, have largely eliminated reps in orthopedics, buying implants directly from the manufacturer at a substantial discount and training surgical technicians to take their place in the OR. Loma Linda’s chief of orthopedics said the hospital has saved about $1 million annually, a savings of about 50 percent on the cost of the devices, without affecting outcomes.

“I think there is a role” for reps, said Lisa McGiffert, director of the Consumer Reports Safe Patient Project. But, she added, when it comes to choosing the best device “can the patient trust that they’re getting the expertise of the doctor or the influence of the rep?”

The presence of device reps in the OR, she added, also raises questions about the adequacy of consent, if patients are not explicitly informed of their presence.

ECRI recently repeated its recommendation that hospitals obtain explicit written consent from patients if reps are to be present and warned surgeons against learning “how to use … devices on the fly.”

How often that happens is unclear. A small 2014 study suggests that reps’ over-involvement is not uncommon.

A survey conducted by researchers at New York’s Albany Medical College found that 88 percent of 43 device reps said they had provided verbal instructions to a doctor during surgery, while 37 percent had participated in a surgery in which they felt their involvement was excessive, often because the surgeon lacked sufficient expertise. Twenty-one percent said they had direct physical contact with hospital staff or a patient during an operation, which could violate hospital policy as well as state law.

Terry Chang, associate general counsel of AdvaMed, a device industry trade association, points to its code of ethics as well as newly revised guidelines issued by the American College of Surgeons, which state that reps are to refrain from medical decisionmaking and participating in surgery.

But Chang says that reps, who have witnessed dozens if not hundreds of the same procedures, provide an essential benefit for doctors and patients. They “are only present at the behest of the physician and only as a trainer,” and they provide “a live interactive resource.”

Gerald Williams, a Philadelphia joint replacement specialist who is president of the 18,000-member American Academy of Orthopaedic Surgeons, agrees. “Even if a surgeon is extremely familiar” with a device, “there are different teams scrubbing in” who typically have less familiarity with the procedure and the surgeon’s process than a rep with whom a surgeon regularly works.

“Their presence is dictated by the complexity of the surgery,” he said. “They are probably there close to 100 percent in complicated cases such as spine surgery and joint implants.”

Williams said he doesn’t tell his patients that a rep will be in the room, adding, “I don’t tell them there’s a circulating nurse, either. My patients look at me as being the captain of the ship. I think if I told them about a rep, they would all be supportive of it.”