3M won the first round in the legal dispute over its patient-warming system, but the battle is far from over.

More than 4,700 people are suing Maplewood-based 3M Co. over its Bair Hugger system, alleging the company’s device most likely caused their devastating surgical infections, even though it’s intended to reduce infections. 3M prevailed in the first Bair Hugger trial late last month in federal court in Minneapolis, but the plaintiffs’ attorneys are vowing to continue the fight, through appeals and fresh trials.

“We all remain committed to the case,” said Minneapolis’ Genevieve Zimmerman, one of the co-lead attorneys in the sprawling multidistrict federal litigation against 3M’s Bair Hugger device. “We think it’s a dangerous product. And we will pursue the litigation vigorously on behalf of our clients.”

3M staunchly defends the safety of the Bair Hugger, a device invented in Minnesota that has grown into a dominant product in the $1.5 billion market for devices that are used in hospitals to prevent hypothermia during surgery. Maintaining a normal body temperature during surgery has long been thought to speed recovery times and enable the body to better ward off infection.

“The science is the science, and the science supports use of the Bair Hugger patient warming therapy. No valid science has found that the Bair Hugger warming blanket causes or increases the risk of surgical site infections,” 3M spokeswoman Donna Fleming Runyon said via e-mail. “3M does not see anything about the other cases under consideration for bellwether trials that make them any stronger for the plaintiffs’ lawyers.”

A bellwether trial is when a case is allowed to go to trial to test the evidence and legal theories behind a larger group of lawsuits.

Searing pain

South Carolina retiree Louis Gareis, 76, lost the first case against 3M late last month by jury verdict. He alleges the Bair Hugger caused an infection after a 2010 hip replacement surgery.

His attorneys say that decisions by U.S. District Judge Joan Ericksen to prevent them from presenting important evidence in their case meant the Gareis verdict isn’t representative of the claims in the remaining 4,700 lawsuits.

Gareis was barred from showing jurors an April 10, 2006, e-mail from a clinical affairs director at Bair Hugger’s original maker, Arizant Healthcare, in which the director said promoting a $6 million study of the Bair Hugger’s infection risks would not be a good “career move” for him because of the cost and uncertainty involved. (3M acquired Arizant in 2010.)

Also barred from trial was a 2012 e-mail in which an outside researcher said that he was unhappy 3M had not done a “bacterial sampling study” that could have addressed criticisms that a 2011 published paper had misrepresented the safety of using “forced air” to warm patients, as the Bair Hugger does.

3M successfully argued the documents were irrelevant in a trial focused solely on device design.

Getting an infection after surgery is always serious, but infections of orthopedic implants are especially damaging. Patients with infected artificial joints often undergo at least one more surgery to install new implants, in combination with extensive infection-control measures.

In addition to the pain and emotional toll for patients, prosthetic joint infections create huge costs for the system, with expenses typically exceeding $90,000 per infection, according to a 2017 analysis by the Centers for Disease Control and Prevention published last year in JAMA Surgery.

Causes aren’t clear

Yet the exact causes of such infections remain mysterious. Patients are often told that they simply had bad luck.

“You’ll never know what the answer is,” said Pennsylvania orthopedic surgeon Dr. Kenneth Urish, who is not involved with the litigation. “It’s either there when you put the implants in, or it’s getting there through your wound, or it’s getting there though your blood supply. If it happens in the first year, we look at all three of those options.”

Faced with that lack of a definitive answer, thousands of patients have settled on 3M’s device as the most likely source of infection. Like Gareis, many reached that conclusion after seeing ads for the litigation on TV.

In an interview Friday, Gareis said the doctor who put in his artificial hip in 2010 couldn’t tell him why it became infected. But the infection left Gareis with searing pain, unable to sleep well or run his business, among other things. His medical costs eclipsed $200,000.

“It was a tough experience,” Gareis said. “I thought I was going to die.”

3M attorney Jerry Blackwell of Blackwell Burke in Minneapolis said during the trial that the multinational manufacturer harbored no ill will toward Gareis, but his allegations didn’t match with reality.

No report has ever definitively traced a joint infection to a Bair Hugger device, and the epidemiological studies offered by the plaintiffs aren’t designed to do so. Blackwell told the jurors that the basic-science experiments and computer simulations offered as evidence at trial were speculative and misleading, failing to account for important real-world details like other sources of bacteria in an operating room.

Meanwhile, the medical community is still debating the evidence for surgical patient warming, especially in joint-replacement operations.