Sensors solve knee implant problem

Knee replacement surgery is a common joint replacement procedure, with most such surgeries done to replace an older implant or one that has worn out.

For younger, more active patients, this surgery presents a dilemma. They are expected to remain physically active for their health, but that activity can wear out the new implant.

Often, doctors don't know if patients are overexerting themselves until they develop symptoms, but by that time, the damage to the implant has already been done.

For a young patient, going through knee replacement surgery every five or 10 years is a daunting task, but finding the perfect balance of activity levels to maintain the integrity of the implant has been equally daunting.

To solve this problem, researchers created smarter knee implants that could monitor changes in activity as they happened.

"We are working on a knee implant that has built-in sensors that can monitor how much pressure is being put on the implant, so that doctors can have a clearer understanding of how much activity is negatively affecting the implant," said lead principal investigator Sherry Towfighian.

The sensors allow doctors to tell patients when a certain movement has become too much for the implant, so that patients can quickly adjust and avoid further damage to the implant. It also helps doctors find the sweet spot of activity for each particular patient.

SMART IMPLANT

However, while the sensors solved one problem, they brought in another.

The researchers did not want to power the sensors with a battery that might need to be replaced periodically and therefore, defeat the purpose of a smart implant.

They worked on an energy harvesting mechanism that can power the knee implant from the friction caused when a person moves. They tested the prototype to determine how much power it would generate under equivalent body movements based on body weight.

When someone walks, the friction of the micro-surfaces coming into contact with each other can be used to power the smart knee sensor.

An average person’s walk produces six microwatts of power, while the smart sensor needs 4.6 microwatts.

"The sensors will tell us more about the demands that are placed on implants, and with that knowledge, researchers can start to improve the implants even more," said Towfighian.

The researchers are hopeful that the combination of activity sensors and a self-powered system will increase the life span of knee implants and reduce the need for follow-up surgeries. - Science Daily