Every year, Football Outsiders releases a metric called Adjusted Games Lost. AGL is meant to quantify how much each team was affected by injuries. They based it on two basic ideas:
1. Injuries to starters, injury replacements and important situational reserves impact a team more than injuries to bench warmers.
2. Injury effects should be adjusted for whether or not a player was out, doubtful, questionable or probable.
These both are fairly obvious, but we don't really have other metrics that try and break these down. Every sport deals with injuries, but there inherent physicality of football brings injuries into a whole separate light.
The 49ers ended up first in adjusted games lost, by which I mean they had the fewest games lost of any team. According to FO, the 49ers finished with 16.2 adjusted games lost. In 2011, the 49ers were eighth in the NFL with 38.4 adjusted games lost. What is particularly notable about that 16.2 number is that it is almost half of the second place team (Minnesota Vikings - 30.9).
The 49ers did suffer some very notable injuries on offense, losing Kendall Hunter, Kyle Williams and Mario Manningham. While they did not lose them until fairly late in the season, it is possible things go a bit different if a guy like Manningham had remained healthy. Of course, no Kendall Hunter injury leaves us wondering what would have happened with LaMichael James. You take the bad with the good.
On defense, the most notable injury was to Justin Smith, who missed the last two games with his triceps injury, and was far from 100%. One injury that does not appear to be factored into this would be Parys Haralson's own triceps injury. Had Haralson actually played during the season, it's entirely possible the pass rush would have been a little bit more rested late in the season. Haralson isn't a great pass rushing outside linebacker, but I imagine the team would have been more comfortable playing him than they were once they added Clark Haggans to the picture.
The defensive depth is an area that will need to be addressed this offseason, be it in free agency or the draft. Even if the team maintains this level of health moving forward, there are still issues with players getting worn down. Vic Fangio might like going with limited substitutions, but after seeing the defense wear down late this season, more depth really is a must. We'll see if the 49ers address is accordingly.