What could be the cause of this pain in my knee and foot?

I keep getting a pain in my knee that runs down my shin, and to the top of my foot. The pain doesn’t necessarily "run" down my leg. When the pain comes, the knee, shin, and foot all hurt at the same time. The pain only lasts about 2 seconds, but is literally excrutiating. It [...] http://bit.ly/nmfjlG