3M Co. won a legal victory in Ramsey County court this week in the ongoing litigation from orthopedic surgery patients who blame the company's Bair Hugger forced-air warming systems for causing their deep joint surgical infections.

Ramsey County District Judge William H. Leary III on Monday issued a ruling that dismisses dozens of lawsuits filed by Minnesota residents against the Maplewood-based company. Leary found that the plaintiffs had presented no evidence showing that their theory of the case — that the Bair Hugger may increase the risk of surgical infections — is supported by evidence accepted in the scientific community.

"There is no generally accepted scientific evidence — and plaintiffs offer none — that the risk of infection associated with FAWs [forced-air warming systems] is greater than that associated with patients who are not warmed during surgery," Leary wrote Monday, granting 3M's motion for summary judgment. There was also no generally accepted evidence that other companies' warming devices had lower rates of infection than 3M's, the judge wrote.

3M cheered the ruling, but an attorney for the plaintiffs said the cases are not resolved yet. "Plaintiffs are surprised and disappointed with the Ramsey County Order, and will appeal," plaintiffs' attorney Genevieve Zimmerman said via e-mail Tuesday.

Leary's ruling on the state-court cases doesn't directly impact the much larger federal litigation involving more than 4,000 lawsuits from patients across the country who make substantially the same allegations as the Ramsey County plaintiffs, using many of the same expert witnesses and published studies that failed to persuade Leary.

U.S. District Judge Joan Ericksen ruled in December that plaintiffs can present their expert witness to jurors to support their claims, just as 3M can present their own experts to rebut the allegations.

The first "bellwether" trial in the federal multidistrict litigation (MDL) is slated to begin in the spring.

The Food and Drug Administration says that using systems like the Bair Hugger to keep patients' bodies warm before and during surgery can result in less bleeding, faster recovery times and a lower risk of infection. 3M said its Bair Hugger system, which was originally designed by Minnesota's Dr. Scott Augustine, has been safely used in more than 200 million surgeries over three decades.

But Augustine himself now says that the forced-air system he invented has flaws that increase the risk for infection. Leary's ruling noted that Augustine formed a new company that sells a competing patient-warming device.

In an e-mail, Augustine said he was "very sad" for the Minnesotans who contracted infections but then had their cases dismissed by Leary's ruling. "Judge Leary's opinion ignored the excellent science supporting the plaintiffs' claims," Augustine wrote.

The design flaw in the Bair Hugger, according to the federal and Ramsey County plaintiffs, is that the device creates warm air currents that rise from the floor of the operating room with enough lift to pick up germ-containing particles and deposit them in a surgical wound. The plaintiffs also say that the device's air-blower may harbor bacteria.

Plaintiffs have no direct evidence showing a germ-laden particle traveling from the floor of an operating room and into a surgical wound on a current of air created by the Bair Hugger. However, they do have computer modeling showing that it is possible, a bevy of experts who say it's likely to happen, and published studies that they say support their allegations.

3M says the science behind the safety of its system is sound and supported by numerous experts and studies. In the motion for summary judgment in Ramsey County, company lawyers said plaintiffs presented no evidence of any doctor reporting a Bair Hugger system causing a surgical infection.

The state and federal judges were sitting side by side in court during a three-day hearing last October about expert testimony, yet they reached different conclusions about whether to allow the plaintiffs' experts to testify. However, the judges were applying different legal standards in their analyses.

The federal rules say the judge need only exclude testimony that is so fundamentally unsupported that it cannot offer assistance to the jury. In Minnesota courts, the bar is higher — litigants have to show that evidence supporting expert testimony is generally accepted within the relevant scientific community if the expert is presenting a "novel" theory, such as the Bair Hugger increasing infection risks.

3M spokeswoman Donna Fleming Runyon said Leary's ruling on Monday "affirms our position that there is no generally accepted science that the 3M Bair Hugger system causes infections."

Joe Carlson • 612-673-4779