In mid-December, the Minnesota Vikings began listing tailback Adrian Peterson on their injury report because of an abdomen ailment. In the four games that followed, including a wild-card playoff game, Peterson participated in 77 percent of the team's offensive snaps and rushed for 596 yards en route to winning the NFL's MVP award.

On Thursday, the Vikings revealed the nature of the injury. It was a sports hernia, a painful ailment that almost always interrupts an NFL player's season. Peterson had surgery Thursday in Philadelphia to repair the injury, 11 days after he played in the Pro Bowl, and the team said in a statement that it expects no long-term concerns.

This news adds another layer to what is already a legendary event. We already knew that Peterson's historic season came within a 13-month span of tearing two ligaments in his left knee. Now we know he played at least a quarter of his 17 games with an injury that usually requires in-season surgery.

At least two NFC North players encountered similar troubles, and neither was able to play through it. Green Bay Packers receiver Greg Jennings and Vikings guard Geoff Schwartz both had surgery shortly after their injuries.

Former NFL offensive lineman Ross Tucker, who records a regular podcast on ESPN.com, tweeted: "Played my senior year w/ a sports hernia and can't believe A. Peterson ran for 2K with one. Totally insane."

In retrospect, there were only a few clues that Peterson was hampered at all by a significant injury. He stopped practicing for the most part near the end of the regular season, a decision that seemed reasonable in order to keep him fresh for the playoff run. Peterson also removed himself from the Week 16 game at the Houston Texans, giving way to backup Toby Gerhart on a fourth-quarter goal-line play that netted the clinching touchdown of a 23-6 victory.

Regardless, we can now add another layer to the history we saw unfold last fall.