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This Gross Sound Your Knee Makes Could Be a Sign of Health

Scientists are developing a microphone knee band to measure the sounds of an injured joint's healing progress.
Image: Georgia Tech.

The cracking, snapping sounds of your knee joint might make you shudder, but could also be indicative of the joint's health. In the case of an injured knee, a device that helps a doctor listen to the noises it makes upon movement may help determine how much healing has occurred or whether the patient needs more therapy.

That's why researchers at Georgia Institute of Technology are currently developing a knee band equipped with microphones and vibration sensors to measure the sounds of the joint. The device's piezoelectric film mics don't measure sounds in the air, but the vibrations in the skin. A joint's gross cracking noise, called "crepitus," could indicate instant progress.


"I actually feel like there's some real information in [the noises] that can be exploited for the purposes of helping people with rehab," said Omer Inan, assistant professor of electrical and computer engineering, former discus thrower, and knee injury patient, who pitched the knee band idea. "It's a little bit like some kind of Halloween stuff happening. You're listening to your bones rubbing on each other, or maybe cartilage."

An unhealthy knee produces more erratic noises, than a consistent pattern of sound, Inan said. His research team graphs out recorded audio and matches it to the knee's range of motion to identify when and where the joint makes cracking noises.

With great faith in the acoustic sensing technology, Inan hopes medical research will eventually decode useful information out of noise patterns, and that the in-progress knee band could eventually lead to cheap, wearable monitors to help patients collect information on their injured knees and better monitor their healing progress.

The knee band monitor also uses some of the same technology in smartphones. MEMS, or micro-electromechanical systems microphones, work better with current technologies and are cheaper, costing only up to a dollar.

The technology could be useful for anyone, including athletes, the elderly, and soldiers. "These proposed methods have the potential for enabling knee joint acoustics measurement outside the clinic/lab," reads Inan and colleagues' research paper, "and permitting long-term monitoring of knee health for patients rehabilitating an acute knee joint injury."