I just stumbled upon this while searching for NFL injury stats.
http://www.footballoutsiders.com/stat-analysis/2014/2013-adjusted-games-lost
Football Outsiders put together this "Adjusted Games Lost (AGL)" count. It's basically a value assigned based on injuries that prevent play, injuries that hinder play, and replacement performance for injured players. A low value is good and indicates that a team did not have many injuries or injuries didn't have a big impact on the team. A high value is the opposite.
How they describe it
Injuries are an unfortunate part of the game, but those teams overcame some big ones to make it to the final four in 2013. There were of course many more injuries suffered along the way, and the severity and duration can vary greatly. Sometimes the player makes it back in time, while some teams have to prep a third starter after the backup gets injured as well.
With Football Outsiders' Adjusted Games Lost (AGL) metric, we are able to quantify how much teams were affected by injuries based on two principles: (1) Injuries to starters, injury replacements and important situational reserves matter more than injuries to bench warmers; and (2) Injured players who do take the field are usually playing with reduced ability, which is why Adjusted Games Lost is based not strictly on whether the player is active for the game or not, but instead is based on the player's listed status that week (IR/PUP, out, doubtful, questionable or probable).
As long as NFL teams are solely responsible for producing weekly injury reports, we cannot say that every single injury has been accounted for, but secrecy is an unavoidable aspect of this side of the game.
Ranking from lowest to highest
In 2013, the Lions ended up with a scores of 64.5 putting them 15th in the league, middle of the pack as far as injuries go.
Top 3 were KC, Philly, and Cincinnati
Bottom 3 were NYG, Indy, and GB
How the Lions compared to the rest of the North
Minnesota 55.4
Chicago 62.6
Detroit 64.5
Green Bay 104.5
As far team units go (offense/defense), the Lions were neither in the top 8 nor bottom 8.
As far as individual positions (? = neither top 8 nor bottom 8)
QB 0.0 (top 8)
RB ?
WR 19.0 (bottom 8)
TE ?
OL ?
DL 18.5 (bottom 8)
LB 0.9 (top 8)
DB ?