A:

The XT9 Energy Storing Prosthetic Knee is different then any other knee on the market because it was designed specifically to fill the gap that great walking/running knees leave behind. The XT9 ESPK works well for dynamic energy storing and return during flexion and extension of the knee in an athletic stance -such as on a board- and for shock absorbing -during skiing and other activities.
The XT9 is a specialized sporting knee. Just as ski boots allow the user to ski in a way they never could with normal shoes, but doesn't work well for normal activities itself, the XT9 allows the user to do things they never could with a general purpose knee but does not work well for general purposes itself.