Inside Slant: Narrow focus on ACL injuries

An NFL memo reporting favorable statistics for ACL and other knee injuries this season found its way to multiple media outlets Thursday, and there are some important distinctions between it and the figures we have been discussing on ESPN.com.

According to a portion of the memo, excerpted on the league's "NFL Evolution" website, 30 ACL injuries occurred in games "through the preseason and the first 13 weeks of the season." That total is lower than the comparable time periods in the past five years, but by definition it does not include injuries that occurred in training camps, minicamps, organized team activities (OTAs) or regular-season practices.

The way I read the memo, the figures confirm only a portion of the larger injury story, and it's one we have already acknowledged and agreed with. There is no data to tell us that new rules discouraging hits to the head have led to an increase in ACL-damaging hits to the legs, as once feared. There have been some isolated but high-profile instances, most notably involving New England Patriots tight end Rob Gronkowski, but both the raw numbers and an individual analysis of the injuries reveal no connected uptick.

Games are an accurate barometer of the new rules' impact because tackling rarely occurs in practice. But games can't possibly tell the full story of ACL injuries to trauma in other knee ligaments or other injuries.

Several times this season, we have cited ESPN Stats & Information research noting that more players have been sent to injured reserve with confirmed ACL injuries than in either of the previous two years. Some of those injuries, of course, occurred in practices and thus wouldn't be part of an analysis on the new rules. We've noted that the majority of these ACL injuries have occurred on grass fields and that commissioner Roger Goodell questioned whether shoe choice could play a role in ACL injuries.

ESPN recently expanded its research to include all knee injuries, ACL or otherwise, that have forced a player to injured reserve. That number stands at 121 so far this season, topped most recently by Denver Broncos linebacker Von Miller and St. Louis Rams tackle Jake Long, and it matches the 17-week total of 2012. In 2011, there were 93 such instances.

In fairness, players on injured reserve don't provide a complete picture, either. Not all injuries require a trip to injured reserve. But the issue isn't simply whether the new rules have impacted ACL injuries. There are many other factors to consider, including whether reduced training time -- as negotiated in the 2011 collective bargaining agreement (CBA) -- has left players more vulnerable to ligament and muscle injuries.

A memo about injuries in games can't answer that question. The one in question provides more definitive information than we had, but it can't possibly be interpreted to mean that ACL injuries are down overall in 2013.