Sport: Weak in the Knees

In any contact sport, the danger of injury is always present. In football, sooner or later, everyone gets hurt—and more often than not, he gets hurt in the knee. Obviously, the football player's knee is crucial. It must function perfectly to permit all the feinting, cutting, spinning, twisting, blocking, running and tackling that are the basic elements of his increasingly violent trade.

But the knee is also one of the weakest and most vulnerable joints in the human body—as two of football's most talented practitioners discovered this month. Notre Dame Quarterback Terry Hanratty tried...