Yahoo News : Knee injuries sideline many NFL stars in 2011 (Yahoo

[Coach]

Knees do everything in football. They cause legs to bend the right way. Without them, runners wouldn't be able to turn quickly in traffic. Receivers wouldn't be able to jump in the air to catch passes. Quarterbacks wouldn't be able to get enough momentum on long passes.

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[honda522]

Its just side effects of lockouts..