I'm guessing by classifying this as a cobalt-chrome alloy, but it's a reasonable guess. I think this may be an older design, and may even be stainless steel: I need to test it.
It's a very lovely piece of machinery, though you would click a bit walking with it. What's really fun is the thoughtful labeling that identifies the front. Otherwise you might end up with a knee that bends the wrong way, if your doctor got it backwards, which, I suppose, someone must have been worried about or they wouldn't have put the label on.
Source: eBay seller smeezle
Contributor: Theodore Gray
Acquired: 20 December, 2003
Text Updated: 11 March, 2007
Sample Group: Body Parts+Medical