Sound foundations: Dr. Karen Kruger’s innovations in biomedical engineering are helping young patients navigate pediatric foot conditions

Dr. Karen Kruger loves a complex problem. A biomedical and mechanical engineer by trade, she's not one to shy away from technical challenges. So, it's no wonder that she has focused the last decade of her career on a subject with many moving parts: pediatric foot deformities.

"The foot is really complex," says Kruger, co-director of the Marquette and Medical College of Wisconsin Orthopaedic and Rehabilitation Engineering Center, or OREC. "There are multiple bones and joints articulating in each foot, and then when you add in a complex pediatric onset condition like cerebral palsy or clubfoot, you just compound the complexity of this area of the body."

Addressing foot conditions in early childhood means fewer complications down the road. Untreated clubfoot, for example, makes it difficult for children to walk once they grow past infancy. They might struggle to find shoes that fit properly or develop chronic pain that they carry into adulthood. But the assessments that Kruger is developing help doctors identify personalized solutions for each patient to correct deformities and prevent pain.

Now a research associate professor in the Marquette and MCW Joint Department of Biomedical Engineering, Kruger has designed new mathematical models for pediatric diagnostics, researched better X-ray and 3D imaging techniques, and ​​built a device for doctors to identify orthopaedic conditions earlier in young patients. And in keeping with the rich tradition of patient care established at OREC, she works closely with clinicians to inform her work and bring cutting-edge tools to patient care settings where they are deeply needed.

Dr. Gerald Harris, co-director of OREC and Kruger's mentor, calls her a "hybrid engineer": someone who is equally well versed in rigorous scientific study and the patient-forward, clinical side of research. "She has the technical skills to elevate this marriage between technology and clinical applications and has taken them to the next level," he says.

Child-sized solutions for foot care

Recently, Kruger was awarded a $3.2 million R01 grant from the National Institutes of Health for further study of pediatric flat foot deformities. This work will focus on building and testing a weight-bearing computational tomography, or WBCT, device for children, adapted from diagnostic tools used for adults. It will help surgeons identify flat foot incidence much earlier and plan for surgical interventions before issues become chronic (such as challenges with gait and mobility).

When left untreated, these issues can develop into lifelong disabilities. Pediatric flat foot incidence affects as many as 44 percent of children, and because it is often not addressed until adulthood, moves toward earlier intervention will catch worsening symptoms and make an important difference for thousands of children and their families.

Kruger is working with a team of engineers and orthopaedic surgeons to bring the modified WBCT device to life, including colleagues at Shriners Children's Hospital in Chicago, where she is an investigator in the Motion Analysis Center.

The WBCT device is essentially a vertical CT scanner that maps out the feet and ankles of each patient as they stand on a platform. "Being able to capture what they actually look like standing was a big advancement for the field," Kruger says. With the new R01 grant funding, Kruger and her research partners will conduct a multisite study on patients with flat feet to determine how well the new device works compared with the current standard of care. The work brings together a multidisciplinary research consortium that includes Shriners Children's; the University of Utah; University of California, Davis; University of Nebraska Medical Center; and the Medical College of Wisconsin.

The work is deeply personal for her, too. Kruger has a 9-year-old daughter who is a Shriners patient. "We really have an opportunity to give the surgeons better tools to help them make more informed decisions," she explains.

The road to pediatrics

Kruger started her career entrenched in the engineering world but took an early interest in surgical interventions. For her Ph.D. dissertation presented at the University of Iowa in 2014, she used computational modeling to study the longevity of total hip replacements - a growing concern, as this surgery is performed on younger patients with greater implant demands. "I was just kind of fascinated with that from an engineering perspective as an undergrad," she explains.

But it wasn't until she arrived at Marquette in 2015 that Kruger first found herself working on pediatric applications. She received an Advanced Rehabilitation Research Training, or ARRT, grant to work as a fellow at OREC, where she first met Harris. Together, they collaborated on projects at Shriners, working on new modeling methods to quantify motion. That early work became the foundation for the Shriners Children's Gait Model, a universal framework for motion analysis published in 2024 that helps pediatricians diagnose patients more accurately.

Her ARRT fellowship "made me realize how many unmet needs there are in pediatric orthopaedics specifically," Kruger says. With her connections to OREC and Shriners, she understood that she was in a unique position to help address those gaps. She stayed on staff as an engineer at the hospital's Motion Analysis Center and a research assistant professor at Marquette after the fellowship ended.

Under the direction of Harris, who founded OREC in 1999, Kruger has spent much of the past 10 years contributing to efforts that have earned international recognition. In addition to its pediatric research muscle, OREC leaders also oversee community programs for children with disabilities and operate motion analysis clinics in five countries around the globe. Marquette researchers associated with OREC have been awarded more than $12.5 million in government and foundation funding in the past two decades.

And Kruger has been at the center of it all, helping OREC grow into the powerhouse it is today. "She represents the vanguard for OREC research," says Harris.

Taking the helm

In 2025, Kruger was promoted to co-director of OREC's research arm. She now oversees all collaborative projects between OREC, MCW, Marquette and research partners at universities around the country.

"Dr. Karen Kruger exemplifies the best of what a biomedical engineering leader can be," says Dr. Kristina Ropella, Opus Dean of Marquette's Opus College of Engineering. "She is highly collaborative across disciplines and institutions, committed to translational outcomes to serve real patients, and a true champion for underserved patient populations."

With the current R01 grant funding, Kruger says, OREC researchers will continue studying flat foot and the use of the WBCT device for diagnosis. But they already have a list of about 20 projects they'd like to pursue after learning what they can from initial studies.

As it has in the past, OREC's future research will remain focused on children - a patient population that Kruger says is often overlooked in orthopaedics. "I think we really have an opportunity to tackle some of these harder problems, especially with the big collaboration we have built up from this grant," she says.