Knees are among our hardest-working joints. They help us walk, pivot, jump and climb stairs.
But strain, pain and diseases like arthritis can damage them so badly they need to be replaced. And unless they’re designed, installed and loaded properly, knee replacements can also fail sometimes.
Now a Western professor of mechanical and materials engineering is working with an international team to help knee replacements last longer.
Ryan Willing is co-investigator in a US$2.3-million project to test novel, friction-powered sensors that would be implanted with knee replacements to indicate the health of the joint.
The grant, from the U.S. National Institutes of Health’s National Institute of Arthritis and Musculoskeletal and Skin Diseases, is the next stride in the research after a proof-of-concept grant was awarded to the team in 2019.
“We’re still very much at the pre-clinical stage but this is a big step forward,” said Willing, who is also a member of Western’s Bone & Joint Institute.
Mechanics of recovery
About four million people in the U.S. have total knee replacements: operations in which the damaged knee bones are re-sculpted and capped with metal and plastic components.
If the joint is still uncomfortable, painful, or if the implants fail – as they could do in 10, 15, 20 years – surgeons can sometimes try “revision surgery,” another implant in an attempt to reduce pain and bring back normal knee function.
Ideally, though, researchers want to extend the life of the first implant by monitoring and responding to knee stresses as they occur. Measuring what’s happening inside the joint would provide the opportunity to alert health-care providers if something is wrong with the joint, and help with clinical decision-making to address these problems – perhaps avoiding that painful second surgery.
That’s what Willing and his collaborator Brent Lanting, who is a professor at Schulich School of Medicine & Dentistry and an orthopedic surgeon at London Health Sciences Centre, are trying to do. The project is led by Binghamton University engineering professor Shahrzad “Sherry” Towfighian with co-investigators from Stony Brook University in New York. (Willing was formerly a professor at Binghamton).
They’re working to develop and test a self-powered knee load sensor, encased in a flexible but durable material, to send signals of the knee’s health to the world outside the body.
Inserted between two components of the knee replacement, the sensor would consist of two paper-thin plates a hair’s-width apart from each other. When a patient is walking, the plates would connect with each other and the friction would generate a microwatt signal that could then be analyzed (through a smartphone app, for example) to determine if the knee is responding as it should.
Willing’s lab will test prototypes using a joint motion simulator, a sophisticated machine that replicates and measures the force, motion and stability a knee experiences during rotation, bending, impact and pressure such as walking downstairs.
“We need to determine: does it work in the lab? Does it work in a machine that replicates the load on a knee? Does it work in a human joint? And if so, does the wear and durability of the sensor outlast the durability of the knee implant?”
And if it works on knees, Willing said, it could spare many patients a lot of pain and potential additional surgery.
The technology could even be tailored to other joint replacement implants, such as shoulder joints, which use similar materials and could benefit from embedded load sensors, Willing said.