There actually was a prosthetic leg called the Power Knee featured in the segment, that has a similar class of capability as the Luke Arm.
More info about the Power Knee can be found here:
http://www.ossur.com/bionictechnology/powerknee
Videos of the Power Knee in action:
http://www.youtube.com/watch?v=zUBaYs8Y7F4
http://www.youtube.com/watch?v=6NhQm...eature=related
There are other similar devices as well such as the
C-leg