3M Co. is battling lawsuits from more than 50 orthopedic surgery patients who say the company's popular "Bair Hugger" warming blankets, used to keep people warm before surgery, circulated contaminants and caused debilitating deep-joint infections.

The Bair Hugger forced-air warming blanket has been used in more than 200 million surgeries since 1987, and lawyers for the Maplewood-based manufacturer say no study has proved that it causes surgical infections. But a skirmish over the science is shaping up, with new lawsuits being filed daily and plaintiffs' attorneys eyeing a potential national suit with thousands of plaintiffs.

"3M will vigorously defend the product and the science against these unwarranted lawsuits," company spokeswoman Donna Fleming Runyon said. "We think it's unfortunate that the plaintiffs' attorneys are using bad science to blame their clients' infections on a device that has helped so many people."

3M paid about $800 million in 2010 to acquire Arizant, the Eden Prairie-based maker of the Bair Hugger. The single-use device is used in four out of five U.S. hospitals today.

Attorneys representing the injured patients say the research shows the device can spread airborne contaminants while warming up surgical patients. The inventor of the device, Dr. Scott Augustine, is expected to testify that the device he developed in the late 1980s creates infection risk, especially for joint-surgery patients.

"There is no question that it's a true phenomenon. It's happening. And it's easy to show," said Augustine, the Twin Cities anesthesiologist and entrepreneur who now opposes use of the Bair Hugger because of the infection risk. "With regard to orthopedic infections, a scare is what's needed. This product should never be on another orthopedic patient."

Augustine is a controversial figure. He pleaded guilty to a health care-related misdemeanor in 2004 and was ordered to pay a $2 million fine, though he has denied doing anything wrong. Today he is the chief executive of Eden Prairie's Augustine Temperature Management, which sells a competing patient-warming device called the HotDog that uses conductive heat similar to an electric blanket, rather than forced air.

Augustine said he regularly gives lectures to health care professionals about his concerns regarding the device. Last week, a news release from 3M cheered a ruling by a federal judge that will force Augustine to turn over documents and answer questions about his role in promoting the alleged risks about the Bair Hugger.

"To come in and besmirch and disparage a product that actually leads to positive surgical outcomes with an attempt to scare people … for litigation or competitor-product purposes is a public disservice," said Jerry Blackwell, 3M's Minneapolis-based national trial attorney for the Bair Hugger injury lawsuits.

3M sells an array of disposable Bair Hugger patient-warming blankets, retailing for between $6 and $24 apiece. The blankets include rows of inflatable tubes that fill up with hot air to warm patients, which is thought to improve surgical outcomes by preventing heat loss from the body's core and reducing the risk of hypothermia from anesthesia.

A separate warming unit, which is connected by a hose, pumps air into the Bair Hugger blanket.

Augustine says that Arizant "stumbled onto" the discovery that the warming unit can disrupt the carefully designed flow of sterile air inside an operating room. He said waste heat from the unit builds up under the operating table and creates convection currents that can stir up contaminants from the floor and embed them on the surface of a knee or hip implant.

"We studied this extensively for about 18 months. I can tell you with 100 percent certainty that the waste heat rises every single time. This was reported before 3M even bought the company," Augustine said. "3M can say that it doesn't happen. … But when you are going against a basic law of physics, it's kind of an absurd thing to say."

In November 2011, the Bone and Joint Journal in the United Kingdom published a paper from a study of experiments with mannequins and research on past patient records that found the Bair Hugger created a "significant" increased risk for deep-joint infection compared with patients who used the HotDog. The study used statistical regression to report an infection rate of 3.1 percent with forced air, compared with 0.8 percent with the HotDog.

The findings did not trigger a sea change in patient-warming.

Medical-evidence organization ECRI Institute closely evaluated the Bair Hugger and HotDog data and concluded in a 2014 technology assessment that there wasn't enough evidence either way to determine whether one system was better at reducing surgery-related infections.

A systematic review of past studies published in the Journal of Bone and Joint Surgery in Massachusetts last year concluded, "forced air warming can impact [air] flow under certain very specific conditions, but any actual clinical impact on surgical site infections must be considered unproven at this time."

3M says the Bair Hugger's safety is supported by 60 randomized controlled clinical trials since its development in 1987.

"We're hopeful to have a court take a look at, on the very front end, the question of what is the science that supports a claim that the Bair Hugger causes any type of infection, much less a surgical-site infection," 3M attorney Blackwell said. "If there is no competent medical and scientific proof to establish that, then there is no basis for any of these lawsuits. And we contend there is no basis for any of these lawsuits."

Minneapolis-based plaintiff's attorney Anthony Nemo, who represents some of the 50 people suing 3M, acknowledged that the cases could be tough to prove in court because no one has direct evidence showing the Bair Hugger stirring up contaminants then and placing them into any particular patient's surgical wound.

"In any infection case, you have to prove that what you are claiming is more likely than not the cause," Nemo said, noting that similar indirect evidence on relative risks was the basis for tens of thousands of lawsuits filed against drugmaker Merck & Co. over its flawed pain drug Vioxx.

Merck eventually agreed to pay $4.85 billion to resolve those cases.

Twitter: @_JoeCarlson