Injury is part of the game when the game is professional football. Some teams seem more injury prone than others and are hit harder by the losses of key players.
A handy chart published on Reddit shows the impact of injuries on all thirty-two teams. According to this metric, called Adjusted Games Lost (AGL) and originally created by Football Outsiders, injuries to starters are weighted heavier than injuries to guys on the bench.
In 2013 the Steelers were ranked 24th in the league in terms of health. That was the season the Steelers offensive line was plagued with injuries, including Maurkice Pouncey leaving the first game of the year and his backup center Fernando Velasco rupturing his Achilles in November. A slew of other players were placed on IR that year including Larry Foote, LaRod Stephens-Howling, and Sean Spence.
The Steelers fared much better in 2014, jumping up to fourth healthiest in the league ahead of all of their division opponents. Unfortunately, despite the healthy year, the Steelers postseason ended largely due to Le'Veon Bell's absence due to injury, a situation that underscored the importance of a healthy team.
The New York Giants, San Diego Chargers, and Indianapolis Colts are the most unhealthy teams in the league.