Knee Extension Device
The KED is an orthotic device built for Max Conserva to increase the extension force of his right knee. When he was 8 years old, Max was involved in a life changing accident that greatly damaged the quadriceps on his right knee, leaving them unable to bear weight without pain. I was the principal designer, with support from Marshall Haltom in design and logistics. Eddie Momanyi and Jesse Shapiro provided testing support, and it was based on initial groundwork by Marshall Haltom and Susan Nitta.
The KED works by shifting the flexion strength of Max's right knee to extension, by use of a tensile rubber cord running over his right knee. This rubber cord also moves over rollers that allow the tension at the top and bottom of the cord to equalize, and change the moment arm of the cord increasing tension nonlinearly deep in a bend. The cords are also easily removeable, allowing different tensions and preloads for different activities by quickly swapping bands.
Many different geometries and tensile elements were tested, but we ultimately settled on a natural latex rubber because it was compliant and did not require dangerous concentrations of force, and a progressive roller cam that drastically increased force in a deep bend, and to allowed rolling to keep the tension in the rubber constant over its length during stretching. Direct user testing was critical, as Max had insights into how each design felt and responded to complex motions like walking, running and jumping.
Once the design was decided upon, I machined a prototype from aluminum to test a proposed finalized geometry. This was designed to stand to last longer than our rapid prototypes, and be a more permanent fixture on Max's brace. This allowed us to test longer term usability during extended workouts and runs. This prototype functioned well, but after a week the aluminum exhibited aggressive wear, and we decided the final part would should be made from stainless steel for wear and corrosion reasons.
Due to the nature of Max's injury, after time and testing there were always ways to improve his brace. This was the final prototype we could make during our one quarter developing this solution for Max. It was machined by a machine shop from 303 stainless steel, so that he could use it in more corrosive conditions such as biking in the rain or snowboarding, and so that it would wear slower with normal use. He now uses it daily and it is a staple on his website, GoodLeg.org. Special thanks to Max Conserva for being brave enough to let us strap untested devices to his leg.