Engineer helps people stay on their feet

Nate Callithen stands outside Zimmer Biomet in Indiana, where he works on artificial knee development. • Images Submitted

By Tom Victoria 

Nate Callithen helps folks keep walking. He is a development engineer for an Indiana company that makes artificial knee replacements. 

Nate, 22, a native of Western Pennsylvania, said the need for knee replacements has increased over time. 

"People live longer and want to stay active," he said. "They want to wake up and not feel pain. It's really the quality of life." 

Nate explained there are numerous facets to knee replacements, including the recipient's body. 

A graphic from iStock contrasts a healthy knee with an arthritic one.

"Everyone has a different knee geometry,” he said. “Things like gender, age, height, activity level and gait can affect knee geometry.” 

Nate’s employer, Zimmer Biomet in Indiana, designed the Persona system to account for those factors. 

He explained the skeleton changes as the person ages, leading to the need for knee replacements. 

“Bones over time become more brittle,” Nate said. “This is because the bone composition of a younger person has more organic material, which is more elastic. But over time, less and less cells are produced. It is then replaced by minerals, which make the bones more brittle. Additionally, the more active a person is, the more cartilage is worn down. Cartilage acts as a cushion between the bones and is where articulation happens, basically the femur and tibia rubbing up against each other. Cartilage is also an organic material. As we age, we produce less of it. What can happen then is there might be locations in the joint where there is no cartilage present and the physical bones rub up against each other. This is where a lot of joint pain, arthritis, can stem.” 

He said the majority of people requiring knee replacements are older, but even children are susceptible to joint deterioration. 

“It’s really dependent case-by-case,” Nate said. 

Another vital facet of knee replacement design is how the human joint was designed by nature, which was once thought to be a hinge that had only one degree of motion. 

“It’s not the hinge joint that they thought it was,” Nate said. 

“People live longer and want to stay active. They want to wake up and not feel pain. It’s really the quality of life.”

He explained the knee, which is more complex than a hip, has six degrees of motion broken up in two different ways. The three translational movements are proximal/distal, toward hip/toward toes; anterior/posterior, moving out in front of the body/moving out behind the body; and medial/lateral, toward the leg and centerline of body/out from the body and centerline. The rotational movements are flexion/extension, bent knee/straight out like when standing; internal/external, rotating around an axis that is the kneecap toward the leg/away from the other leg; and varus/valgus, bottom of knee is rotated toward the centerline of the body/top of knee is rotated toward centerline of the body. 

Nate graduated in 2021 from Case Western University in Ohio, where he obtained a degree in biomedical engineering.

Nate is a 2021 graduate of Case Western Reserve University in Cleveland, Ohio, where he obtained a biomedical engineering degree. He is starting out at Zimmer Biomet by working as a post-market development engineer, improving the design of implants and instruments, re-assessing manufacturing processes and acting as a technical lead for complaints and compliance. 

According to Nate, the typical problem with knee replacements is the patient not heeding medical instructions. 

"The biggest issue is patient noncompliance," he said. 

To address that problem, Zimmer Biomet is developing a “smart knee” called Persona IQ, which received FDA (U.S. Food and Drug Administration) De Novo status, a marketing pathway in which no medical or clinical claims can be made. Nate said the smart knee can collect data on a person’s gait for a minimum of 10 years. 

Nate, third from left, was a college swimmer.

“It can collect things like range of motion, distance travelled, cadence (number of steps per minute), step count, walking speed and stride length. This can help especially in the PT (physical therapy) phase after surgery to track patient progress.” 

Nate was a competitive swimmer in college. In his free time, he still hits the pool. 

"I still go to the Y(YMCA) and work out," Nate said. 

He recommended students pursue engineering if they’re interested in that field. 

"With an engineering degree, you can do almost anything," he said. "(But) you have to be willing to put in the work."