Building on the success of a project that increased strength by adding motors to traditional knee, hip, and ankle braces, a team at the University of Michigan is studying how effective this approach is in reducing knee pain caused by osteoarthritis.
“This has the potential to create entirely new types of orthodontic interventions that don’t currently exist, and could potentially delay surgery or prevent people from having surgery,” said Robert Gregg, UM professor of robotics and leader of the project, which received $2 million in funding from the National Institutes of Health.
In previous research, the exoskeleton, or exos, developed by Greg’s team reduced the effort expended by study participants by:
-
Quadriceps effort with knee lateral flexion is 14.5%
-
Ankle torque reduced by 19.1% with ankle exo
-
25% of the work is done by the hip joint in the hip exos
We conducted a pilot study in four patients with knee osteoarthritis. All experienced pain relief. Reducing the peak strength of a joint reduces the peak load on the contractile muscles that pull the joint. Reduces its peak and relieves arthritis pain. ”
Robert Gregg, Professor of Robotics and Project Leader
Before inviting study participants into the lab, researchers will optimize the exoskeleton to reduce arthritis pain. Greg and his team have extensive experience modeling muscle force and joint torque, but until now they had never looked closely at what was happening inside the joint.
In the future, they plan to take a closer look at musculoskeletal models to quantify how exogenous supplementation reduces bone-on-bone contact forces and therefore pain inside arthritic joints. They will use this information to adapt their exocontrol algorithm to reduce not only muscle effort but also contact force, ultimately assessing the impact on participants’ self-reported pain across different activities.
The control algorithm is based on the “energy shaping” approach espoused by Gregg’s group, which contributed to the early success with brace-based exos. Older control strategies often relied on guessing what the user was going to do, such as going up the stairs or sitting in a chair. Instead, the energy-shaping algorithm looks at your current movements and predicts how much force you’ll need within the next second. This prediction comes from a model of human movement created using motion capture data and physics.
The design of the Exo itself is very similar to previous efforts to increase strength. The team, which includes co-researcher Elliott Rouse, an associate professor of robotics at the University, uses a “pancake” motor popularized in the drone industry. The main advantage of these motors is high torque at low speeds, providing forces similar to human joints.
Previous motors were small enough to attach to knee braces and required more gears to provide higher torque. The gears are louder and harder to drive backwards, resulting in an exo that’s as hard and noisy as a home drill. Pancake motors provide both the power and smooth operation needed to match human motion while being nearly silent.
Clinical trial involving participants with arthritis
Co-investigators Edward Wojzitis, the William S. Smith Legacy Professor of Orthopedics, and Damon Bagley Ayers, a Michigan medically certified orthotist, will recruit participants with osteoarthritis to support the clinical trial. Stephen Hart, associate professor of anesthesiology and internal medicine at the University of Michigan Medical School, supports rigorous pain assessment.
Although the study is a laboratory test, Gregg eventually hopes to send exos home with users to see if it alleviates the cycle of muscle wasting associated with osteoarthritis. Since the exoskeleton facilitates each step, muscle atrophy can worsen if the user does not move more. The research team is betting that if exo users can move with less pain, they will move more often, and the increased cumulative activity levels could strengthen exo users’ muscles.
