If I remember correctly,  it was a very bad tackle but no major injury to the player. And Essien escape the punishment from the referee too. I could be wrong tho.

Riise's rocket hit Smith's leg which caused him to land awkwardly. It was the contact with the ground that caused the break. If a player could actually break another player's leg by simply thumping the ball with all his might, imagine how much damage players who get smacked right in the face would incur.