$20 Knee - The 50 Best Inventions of 2009
Time Magazine

Tens of thousands of amputees in the developing world wear an inexpensive
prosthetic called the Jaipur Foot. But poor patients who lose a knee joint
have few options: a titanium replacement can cost $10,000, and crude models
don't work very well. Now a team of Stanford engineering students has
designed a knee that's not only dirt cheap — just $20 — but also mimics the
natural joint's movements. Developed with the Jaipur Foot group, the
JaipurKnee is made of self-lubricating, oil-filled nylon and is both flexible
and stable, even on irregular terrain. The device is being tested in India;
more than 300 people have been fitted so far.  

The JaipurKnee comprises five pieces of plastic and four nuts and bolts. It
requires no special tools and takes just a few hours to manufacture 

Source:
http://www.time.com/time/specials/packages/article/0,28804,1934027_1934003_1933963,00.html

Links:
An Artificial Knee, for Just $20
http://www.fastcompany.com/blog/cliff-kuang/design-innovation/artificial-knee-just-20?#

Cool product: $20 artificial knee for patients in the developing world
http://news.stanford.edu/pr/2009/pr-limbs-041509.html

$20 artificial knee for patients in the developing world
http://news.stanford.edu/news/2009/april15/cool-product-expo-artificial-limbs-041509.html

The JaipurKnee - Kamal's Story
http://remotiondesigns.org/jaipurknee.html

A $20 prosthetic knee to bring relief to disadvantaged amputees
http://www.gizmag.com/a-20-prosthetic-knee-to-bring-relief-to-disadvantaged-amputees/11514/

Prosthetics for the Poor
http://www.trendhunter.com/trends/prosthetics-poor-jaipurknee-project-artificial-knees-developing-world

Stanford students create a prosthetic leg that works for only $20
http://dvice.com/archives/2009/04/stanford-studen.php