Sam Bradford's durability key for Eagles

PHILADELPHIA -- Sam Bradford tore his anterior cruciate ligament while running out of bounds. He was fending off a tackler, but it appeared his knee buckled on its own. That was the first time.

A year later, during a preseason game, Bradford tried to step away from a defender in the pocket. He went down in a heap. Bradford tore the ACL in the same knee.

For Chip Kelly’s grand remodeling of the Philadelphia Eagles to work, Bradford has to be able to play all or most of the team’s games in 2015. He has had bad luck in each of the past two years, but it is hard not to conclude that a player is injury-prone after a couple of episodes like that.

Kelly has said a few times that many elite quarterbacks have missed whole seasons. He specifically mentions Peyton Manning, Tom Brady and Drew Brees in those examples. The truth is, however, that elite quarterbacks have a tendency to be on the field for nearly every game. It is part of what makes them elite -- their ability to avoid big hits and their teammates’ ability to block for them.

Manning missed the entire 2011 season to have surgery on his neck. The Indianapolis Colts went 2-14 that season, getting into position to draft Andrew Luck first overall in 2012.

But before 2011, Manning played every single game of his career. Beginning in 1999, he started 16 games every year through 2010. He did not miss any of the 19 playoff games the Colts were in. Since missing the 2011 season, Manning has played 53 consecutive games for the Denver Broncos, including playoffs.

So yes, Manning did miss a year. But he has not otherwise missed a single start due to injury since 1999.

Brees signed with the New Orleans Saints after a shoulder injury required surgery. From 2006 through 2014, Brees has missed exactly one game for the Saints. He has been healthy and available for every other game.

Brady? He went down in the season opener in 2008 and missed the rest of the season. From 2001 to 2007, Brady missed only two starts for the New England Patriots. Since 2008, he has missed exactly zero starts.

Aaron Rodgers missed two games in five years before breaking his collarbone in 2013. That cost him seven games. Rodgers has not missed a start since.

Eli Manning has missed zero starts since becoming the New York Giants’ starting quarterback in 2005.

“Quarterback is the position in the National Football League, and you better have a couple of them,” Kelly said Wednesday at the NFL owners meetings. “In my two years here, we’ve played multiple quarterbacks in every season.”

Kelly chose the oft-injured Michael Vick as his starter in 2013. Nick Foles replaced him after Vick went down with a hamstring injury. Foles missed one game in 2013 due to a concussion. He started the first half of the 2014 season before breaking a collarbone. Mark Sanchez started the rest of the way.

Foles was injured when a play broke down. He was moving around in the pocket but was unaware of a defender who had gotten loose behind him. That was pretty much what happened when he sustained the concussion the year before. In both cases, Foles could have avoided the hits with better pocket awareness and by getting rid of the ball.

Kelly believes his sports science-based approach helps keep players healthy and on the field. But as he put it, there’s not much you can do to prevent a broken leg. Linebacker DeMeco Ryans tore his Achilles tendon during a game in Houston. He had torn the Achilles tendon in the other leg a couple of years earlier.

Bradford tore the ACL in his left knee twice in a year. That kind of bad luck will either continue or it won’t. It is clear, though, that having Bradford on the field for an extended period is the key to success for Kelly’s plan.

It's true that he’s had to use two quarterbacks in each of his two seasons in the NFL. But the teams with true franchise quarterbacks don’t rely on their backups to carry the team. Part of being a franchise quarterback is being available for 16 games a season.