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Hearing snap, crackle, pop may help heal your knee

You’ve injured your knee. A doctor straps a listening device to it, and the noises you hear coming out of it are cringe-worthy. “Crackle! Krglkrglkrgl! Snap!”

Your knee isn’t breaking; it’s only bending, and in the future, those sounds could help doctors determine whether the convalescing joint is healthy yet, or if it needs more therapy.

Research engineers at the Georgia Institute of Technology are developing a knee band with microphones and vibration sensors to listen to and measure the sounds inside the joint.

It could lead to a future device to help orthopedic specialists assess damage after an injury and track the progress of recovery.

Former NCAA athlete

Omer Inan has suffered knee pain himself and had been thinking about developing such a device for some time. The assistant professor of electrical and computer engineering is a former discus thrower who was a three-time NCAA All-American at Stanford University and the school record holder.

He spent years whirling around like a tornado, which knees aren’t built for. Add to that the stress and strain of weight training that included squats with 500-pound loads.

“I would always feel like my knee was creaking or popping more if I was putting more stress on it,” Inan said.

Then the Defense Advanced Research Projects Agency (DARPA) issued a call for research proposals on wearable technologies for assisting rehabilitation, and the researcher at the School of Electrical and Computer Engineering pitched his idea.

Inan’s group has published a paper on the latest state of development in the journal IEEE Transactions on Biomedical Engineering online, official print publication is pending. The research is being sponsored by the DARPA Biological Technologies Office. Inan leads a team of 17 researchers, including Georgia Tech faculty in ECE and Applied Physiology and graduate students.

Delightfully gross

When he heard the first recordings of crackly grinding in early experiments, Inan was delighted. “It was a lot louder than expected and a lot clearer,” he said. That meant instant progress.

To others, it just sounds gross. “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,” Inan said.

Doctors call the joint cracking “crepitus,” which rings oddly of “decrepit.”

Some 100 years ago, physicians thought that racket might contain a message and listened to it with large stethoscopes. Now, Inan hopes that in the future, medical research will build on the acoustical sensing technology his group is designing, and eventually decode the sound into useful patterns.

Currently, the researchers are graphing out the recorded audio and matching it to the joint’s range of motion to see where exactly in the leg’s extending and bending the knee creates creaks and pops. The result has peaks and squiggles that resemble an electrocardiogram or other physiological signal.

The acoustic pattern an injured knee produces is markedly different from that of an intact knee. “It’s more erratic,” Inan said. “A healthy knee produces a more consistent pattern of noises.”