July 2020

Young Children Can Benefit From Articulating Knee Prosthesis

Children using new flexible knee prosthetic, which costs the same as the traditional stiff prosthetic, do not show adaptations in gait kinematics.

By Dave Shelles

A new study shows that young children with limb loss will use and benefit from prosthetic knee flexion and extension, if it is available to them. The study counters the current standard of care that uses a stiff prothesis with no knee bend because conventional wisdom promoted that stiff legs were better at developing neuromuscular stability.

According to Mark Geil, chair of Kennesaw State University’s Department of Exercise Science and Sport Management and a professor of exercise science in the Wellstar College of Health and Human Services both at Kennesaw State University in Georgia, children walking with what he called an “early knee” (EK) prosthetics prescription had increased pace and step length over the “traditional-knee” (TK) prosthetics prescription, which are prescribed more often for children who experience limb loss.

“This is the culmination of a long series of experiments investigating how children walk with articulating prosthetic knees,” Geil said. “This last study is a particularly important piece in the series, because it’s the first time anyone has conducted a multi-site study of the two different knee protocols.”

With a grant from the Gerber Foundation, Geil conducted the study in conjunction with Children’s Healthcare of Atlanta and worked with children ages 12 months to 5 years old. Some children were treated with the EK protocol, with a prosthesis that bends at the knee for optimal range of movement, while others were treated with the TK protocol—with a knee that offers no flexibility. A control group of age-matched children without lower-leg limb loss also participated in the study.

The study, which was recently published in the online research journal PLoS ONE, observed the children walking, noting their pace and degrees of flexion during the movement (see Figure 1). All children in the EK group flexed their prosthetic knees during swing. Mean prosthetic peak knee flexion over all steps and all EK children was 59.8˚ ± 8.4˚. The mean for the control group was 68.4˚ ± 3.8˚. Contralateral side knee flexion was 69.3˚ ± 5.8˚ and 75.0˚ ± 5.5˚ for EK and TK, respectively.

Children with prostheses often show adaptions such as vaulting (lunging upward with the ankle to accommodate limited range of movement), hip hiking (pushing the affected hip farther upward with each stride), and circumduction (rotating the hip to swing the leg forward), but in Geil’s study the children with early-knee prostheses showed fewer such adaptations than the children using traditional-knee prosthetics.

“These prostheses are available and have been available,” he said. “The point is that they’re just not commonly prescribed for children below a certain developmental level. That conventional wisdom has been established over the decades, just based on assumptions about how children develop. We’re countering that by collecting concrete evidence that challenges those assumptions.”

Figure 1. Knee flexion angles. Knee flexion angle (degrees), averaged for right and left for control group, and displayed separately for prosthesis side and contralateral side for early knee and traditional knee groups. Reproduced from Geil MD, Safaeepour Z, Giavedoni B, Coulter CP. Walking kinematics in young children with limb loss using early versus traditional prosthetic knee prescription protocols. PLoS ONE. 2020;15(4): e0231401. Use is per the Creative Commons License CC-BY 4.0.

What’s more, Geil’s study observed the early-knee prosthesis costs the same as the traditional-knee prescription protocol, and the service life of the knee is not affected by the early provision.

“The ironic thing is—and we mention this in the article—providing a knee at a younger age doesn’t actually cost anyone anything, at least not in the United States,” he said. “Clinical prosthetics uses a device-based billing and reimbursement system, and the code for the first prosthesis already includes a flexing knee.”

The study concludes that with no monetary cost considerations beyond the traditional-knee protocol, and with children adapting physically to the flexible knee, the early-knee prescription is a viable option to allow children experiencing lower leg amputation to participate fully in their childhoods—from the playground to the playing fields.

Geil said he will next focus his research on the psychological phenomenon of confirmation bias among individuals with limb loss, and how it might influence the use of technologically advanced prosthetic limbs.

Geil has worked on prosthetics since 1997, when he started as an assistant professor of health and performance sciences in Georgia Tech’s College of Human Movement Studies. He earned his undergraduate degree in mechanical engineering and his doctorate in biomedical engineering, and previously published a study in 2013 on children crawling successfully with early-knee prosthetics.

He said he enjoys the application of his engineering training to prosthetics as well as the collaboration with clinicians and kinesiologists to make optimal movement possible.

“Prosthetics is a fascinating health care discipline for me because it combines fundamentals of engineering—solid mechanics, materials science, even heat transfer—with fundamentals of medicine,” he said. “As an engineer, I’m able to view the prosthesis as a mechanical system that can be optimized, but it’s essential to not stop there. We must consider the individual foremost. The prosthesis must enable the unique individual to function as naturally as possible.”

Dave Shelles is a writer with Kennesaw State University Office of Communications in Kennesaw, Georgia.

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