A little light reading:
(actually, it is light if you read the abstracts instead of the papers!)

10 years worth of knee goodies:

Changes on magnetic resonance tomography in the knee joints of marathon runners: a 10 year longitudial study. Wolfgang Krampla. Skeletal Radiology v 37 n7. July 2008.

18 years worth of knee goodies:

Long distance running and knee osteoarthritis: a prospective study. Eliza Chakravarty. American J of Preventative Medicine v25 n2. August 2008.

There's another one I haven't been able to get (but really want) from Journal of Bone and Joint Surgery on the physics of cartilage loading and the reinforcement response in the knee. (Feb 2009) Gotta toodle on over to the Health Science library one of these days... cuz I'm not paying online for it.