This could be preaching to the choir, but two interesting articles ... my order of listing is opposite to order on the website where they are found:
http://orthopedics.about.com/b/2008/10/06/physical-activity-helps-knee-cartilage.htm?nl=1 should have been followed by the first one which was
http://orthopedics.about.com/b/2009/12/01/exercise-may-cause-arthritis.htm <== and this is really a mis-title.

Typically, this site has some good information ....
http://orthopedics.about.com/

Keep on spinning ....

Norm