Heal an Injured Knee? You Need to Listen

Georgia Tech researchers hope their wearable device-- which records and graphs sounds inside injured knees-- will help soldiers and athletes.

Nancy Crotti

Those snap, crackle, pop sounds coming from your knee may someday help physicians discern the extent of an injury and how it's healing.

A research team led by a former NCAA discus thrower is working on a device that can transcribe those sounds into a moving graph, according to a statement from the Georgia Institute of Technology. The knee band has microphones and vibration sensors to listen to and measure the sounds inside the joint.

Omer Inan, an assistant professor of electrical and computer engineering, was a three-time NCAA All-American in the discus at Stanford University. Having whirled around like a tornado and squatted with 500-lb. loads, he knows about knee pain. Onan had been thinking about developing such a device for some time.

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

He pitched his idea to the Defense Advanced Research Projects Agency (DARPA), which was looking for research proposals on wearable technologies to assist rehabilitation. A paper on the device has been published online in the journal IEEE Transactions in Biomedical Engineering online. DARPA's Biological Technologies is sponsoring the research.

The quest to detect useful sounds posed some challenges. The knee joint is surrounded by fluid, which blunts sound waves that are exiting the joint for the skin. Also, when a patient moves around, that causes extraneous noises that can drown out useful sounds.

"The fact that the measurement has to occur by definition during movement is a challenge, because you can't just tell the person to be still and avoid motion artifacts," he said.

The researchers combined microphones with piezoelectric film. The film is a hypersensitive vibration sensor and collects the best sound, but it is very sensitive to interference. The microphones placed against the skin make for an ample backup and for a more practical device.

The knee monitor also takes advantage of a technical advancement you will find in your smart phone. Micro-electromechanical systems microphones, or MEMS, integrate better with current technology than microphones based on previous technologies, and that also makes the microphones downright cheap-50 cents to a dollar-for a very affordable device.

If paired with medical research, Inan's acoustic device could lead to inexpensive, wearable monitors, which could benefit athletes who have overburdened their knees, and elderly patients who have slipped and fallen. DARPA's interest is to cut down on repeat battlefield knee injuries and help get soldiers back to duty safely.

"What most people don't know is that musculoskeletal injuries of the knees and ankles are among the top reasons for discharge for active duty service members," Inan said.

The problem may seem fixed months later, but too often it's not, and the knee is vulnerable to re-injury, he added.

The acoustic pattern an injured knee produces is more erratic than that of an intact knee. 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, according to Georgia Tech.

Inan hopes that medical research will build on the acoustical sensing technology his group is designing, decoding the sound into useful patterns.

Nancy Crotti is a contributor to Qmed.

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