Kinect-based system offers low-cost alternative to motion capture for therapy

By Dave Muoio
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Microsoft may have pulled the plug on Kinect, but research applications for the gaming peripheral continue to trickle out. The latest, from University of Missouri researchers, constitutes a pair of studies suggesting that the technology can be used to power a cheaper alternative to the standard motion analysis equipment used by physical therapists and clinicians.

"In testing the system, we are seeing that it can provide reasonable measurement of hip and knee angles," Trent Guess, associate professor of physical therapy and orthopedics at the University of Missouri, said in a statement. "This means that for only a few hundred dollars, this technology may be able to provide clinics and physical therapists with sufficient information on the lower limbs to assess functional movement.”

Guess and colleagues developed a custom software that, along with the depth cameras of the Kinect, captures the movement and positions of joints. To test the accuracy and feasibility of this low-cost alternative, they conducted evaluations comparing results collected using Kinect 2.0-based system against those from standard motion capture devices.

In the first, published in the Journal of Applied Biomechanics, researchers measured the 3D rotation angles of 39 subjects’ hips and knees during two motions, a drop vertical jump and an isolated frontal plane hip motion. Measurements of these motions by the Kinect within the device’s optimal capture volume were in good agreement with those captured by a Vicon eight-camera, marker-based motion capture system.

The second study, published in Sports Health, examined the knee-ankle separation ratios (KASR) of 38 participants performing vertical jump motions. Researchers measured each exercise simultaneously using the Kinect and Vicon, as well as with two AMTI force plates. Here too they saw strong correlations between each system’s measurements, with the Kinect successfully identifying KASR at initial contact and peak flexion with 95.8 percent reliability.

"Assessment of movement is essential to evaluating injury risk, rehabilitative outcomes and sport performance," Aaron Gray, sports medicine physician at University of Missouri Health Care, said in a statement. "Our research team is working to bring motion analysis testing — which is expensive and time consuming — into orthopedics offices, physical therapy clinics, and athletic facilities using inexpensive and portable technology. Our research has shown that depth camera sensors from video games provide a valid option for motion assessment.”

Microsoft’s gaming peripheral has enjoyed a wealth of homebrew applications over the years both inside and out of medicine. Its first and second iterations hit the market in 2010 and 2013, respectively, with the release of a computer-friendly SDK in 2014 making it even easier for healthcare innovators to put the device through its paces.

Among these are Reflexion Health’s Rehabilitation Measurement Tool for physical therapy, and GestSure’s hands-free computer interface designed for surgeons who need to access radiological images in the operating room. Following the discontinuation announcement in October, these companies and others that relied on Microsoft’s technology told MobiHealthNews that they planned to switch to similar depth cameras that have since come on the market.