According to Eagles coach Andy Reid, quarterback Michael Vick has a crack in his rib cartilage, and running back LeSean McCoy has a crack in a rib bone.
Brian Sennett, chief of sports medicine at the University of Pennsylvania, said the injuries are similar but different.
"The last one inch of the distance from the rib to breast bone is cartilage," Sennett said. "It is different from the kind you'd have in a knee. It looks like a rib, but it's made of a cartilage material that allows you to have flexibility so your rib cage can get bigger. These structures look like ribs but are a rubbery material."