What's with all the ACL injuries in the NFL?

In 2013, it seemed there was an ACL injury almost every week. The Arizona Cardinals suffered two such injuries late in the season -- Tyrann Mathieu and Alameda Ta'amu. When Andre Ellington got hurt in practice, it was also feared that it was his ACL as well.

The fact is that there were a lot more ACL injuries than in previous seasons. In 2013, there were 61.

Here is the finalized @nfl Torn ACL Injury list through Week 17. I have the number at 61. @SeifertESPN @theMMQB pic.twitter.com/VQuZ7Hz0Ii

— ACL Recovery Club (@ACLrecoveryCLUB) January 2, 2014

That's a lot. It was almost double the number in 2012. In 2012, there were 32 and 25 in 2011.

Why is this?

Some blame the new rules that force players to go lower and avoiding hitting opposing players in the helmet.

However, that doesn't explain Ta'amu's injury, which he suffered when he jumped over a player at the end of a play and landed funny.

Over the years, there have been more and more restrictions placed on the amount of contact you can have in practice and the amount of time in practice. This could explain some, as many of these injuries are non-contact injuries (like Ta'amu's).

Is there a solution?

That's the difficult thing. The league has to worry about blows to the head because of the lifelong effects brain injuries cause. There is litigation involved and liability. Leg injuries clearly are lower on the priority list.

Is it possible that, as players have gotten bigger and faster, that we have simply reached the physical limits our bodies' ligaments can handle?

Should the league consider other measures -- larger rosters or limiting playing time? In fact, one idea I saw that I loved years ago was the idea of an 18-game season, but that no player could play more than 16. That would get more playing from more players and perhaps give the players' bodies a break to keep them fresher. The on-field product potentially is of decreased quality because you don't have the best players always playing, but perhaps there would be less injuries.

Even without extending the season like the league has discussed many times, you could even go with a 16-game season in which no player can play more than 15 regular season games.

Because if nothing changes, based on the trends and rules in the league, this might become the norm rather than an anomaly. Then again, if the numbers drop back to 2011-2012 numbers in 2014, it could be that 2013 is just the aberration.