Gruesome injury

Last Thursday night during a preseason NFL game, Tennessee Titans wide receiver Marc Mariani suffered a compound fracture of his tibia and fibula while returning a punt.  I'm going to place the picture of the injury and video at the bottom of the post in case you don't want to see it.  This was a very bad injury.  It likely resulted in an open fracture, where the broken bone(s) punctures the skin.  This can lead to complications from infection because of the open wound.  What type of loading caused this injury?

The type of loading that caused this injury was bending.  Bending occurs when there is tension (think about making an object longer and skinnier) on one side of the bone, and there is compression  (think about making an object shorter and wider) on the other side of the bone.  To fully understand the injury, you must watch this video.  As Mariani is moving forward, his left foot is stepped on by one of his teammates.  This stops the momentum of his foot.  However, his lower leg and the rest of his body continues to move forward due to their inertia.  His lower leg makes contact with the other players leg a few inches above his ankle.  This stops the momentum of his lower leg, but the rest of his body continues to move forward.  The point of contact between Mariani's lower leg and his teammates lower leg basically acts as a fulcrum, and the bending forces placed on the tibia and fibula exceed the strength of the bones, and they fail (break).  Adult bone is weaker in tension than compression, so the fracture likely started on the side opposite of where his leg made contact with his teammate's leg.

Human bone is very strong, and it can withstand a large amount of force before breaking.  In these cases of extreme fractures on the football field, it is often times an example of all the forces being lined up in just the right positions to cause a fracture like this.  If Mariani's teammate had not stepped on his foot, there is a good chance he would not have sustained an injury at all.  The Titans are reporting that surgery went well, and hopefully he will have a chance of returning to the field next year.