For people with knee osteoarthritis, instability in the knee joint can limit function and accelerate the disease process.
In a healthy, stable joint, tissues such as ligaments and muscles hold the two bones of the joint together tightly enough to enable functional movement but not so tight as to limit range of motion. Ligaments are stiff tissues that passively guide and restrain joint motion, while muscles are active tissues that generate forces to drive joint motion.
However, the root cause of joint instability is not well understood.
“Understanding joint instability is a tricky problem because the ligaments and muscles work together to stabilize the joint, so if one of these tissues is deficient, it’s possible that the other helps pick up the slack,” says Josh Roth, an assistant professor in the departments of orthopedics and rehabilitation and mechanical engineering at the University of Wisconsin-Madison. “It’s really difficult using existing techniques to be able to tease apart which structure—ligaments or muscles—is actually contributing to stabilize a joint, or which structure is actually deficient in someone who has an unstable joint.”
To solve this challenge, Roth is using a National Science Foundation CAREER award to develop a device—an active knee exoskeleton—and a systematic method to tease apart the key contributions of ligaments and muscles to knee stability.
Roth’s research could enable clinicians to create better personalized treatment plans for patients with knee osteoarthritis. For instance, if clinicians could identify that a patient’s joint instability is due to a deficiency in their ligaments, then a surgical procedure would be the most effective treatment approach. On the other hand, if the muscle was deficient, then a non-operative, rehabilitation treatment would be the best approach.
“Many patients, especially those with severe osteoarthritis, will require both surgical treatment and rehabilitation, and figuring out how these two structures work together will help guide the surgery as well as the post-surgery rehabilitation to really help an individual patient get back to their activities,” Roth says.
For this project, Roth will use an active knee exoskeleton—a device that resembles a bulky knee brace—to apply forces to a knee joint. In addition, he will leverage ultrasound-based imaging techniques that allow him to measure how much the bones move under the applied loads. Together, these technologies enable a variety of measurements that will allow Roth to determine the dynamic stiffness of the joint. Harnessing these techniques, he will develop a systematic method to unravel the contributions of ligaments and muscles to knee stability. Roth will validate his method and measurements in human cadaver knees using a state-of-the-art robotic testing system.
While his CAREER award project is focused on knee osteoarthritis, Roth says the methods he is developing could apply to other joints or other conditions of the knee as well.
Roth’s active knee exoskeleton is based on a design by collaborator Scott Brandon, who did postdoctoral research at UW-Madison and is now an associate professor at the University of Guelph in Canada. This current device works well in the research setting, but improvements are needed to enable future implementation in the clinic, which is Roth’s end goal to maximize the impact his work can have on patient care. Thus, for the educational component of his project, Roth will sponsor undergraduate student design teams to design a soft, next-generation active knee exoskeleton that can be implemented into healthcare settings. This new device could enable clinical studies of knee osteoarthritis and be integrated into treatments for this disease.
In addition, Roth will develop an entrepreneurial training module based on the NSF Innovation Corps (I-Corps) program for the mechanical engineering and biomedical engineering undergraduate design programs. Students will learn about the customer discovery process, which involves effectively interviewing end users of a product and others in the product ecosystem to understand their needs.
“Thinking you understand a customer need and then knowing how to ask questions in a systematic way to confirm or disprove your hypothesis is an important skill set for entrepreneurs and engineers, since they are ultimately going to be designing a product or process for someone,” Roth says. “I think it will be a very enriching experience for students to talk with end users and develop this valuable skill.”
Featured image caption: Assistant Professor Josh Roth (left) works with a state-of-the-art robotic testing system to study knee joints in his lab at UW-Madison. Credit: Joel Hallberg.