Tom Brady escapes serious injury to his knee

The New England Patriots got a scare Wednesday when quarterback Tom Brady hurt his left knee during a pile up in a joint scrimmage with the Tampa Bay Buccaneers on Wednesday.

During full team work, Buccaneers defensive end Adrian Clayborn bull-rushed Patriots left tackle Nate Solder into the side of Brady's left leg as Brady was throwing. All three players hit the turf. Brady rocked backward on the ground holding his knee. He was, however, able to get up and limp off the field under his own power.

He returned for a few more plays before talking with coach Bill Belichick and leaving the field for good with trainers.

An MRI on Brady's knee showed no structural damage, a person with knowledge of the exam told USA TODAY Sports. The person spoke on the condition on anonymity since the Patriots did not publicly reveal the results. Brady is considered day-to-day with a mild sprain.

Tom Brady tore the anterior cruciate ligament in his left knee in the 2008 season opener and missed the rest of the season, but he's played every game since then.

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In the first two-plus weeks of training camp, there have been at least 15 season-ending knee injuries. Even Atlanta Falcons President Rich McKay, the chairman of the NFL's Competition Committee, told USA TODAY Sports, he thinks "there have been more ACL injuries than ever."

According to Edgeworth Economics, which recently conducted an independent analysis of the data provided by the NFL Players Association, ACL injuries are on the rise, although the research doesn't differentiate between a sprain and a tear.

For instance, in the 2004 preseason, there were 13 ACL injuries. That number jumped to 24 in last year's preseason, and it appears the 2013 preseason could surpass that.

"The majority of ACL tears are non-contact tears," said orthopedist Neal ElAttrache from the Kerlan-Jobe Orthopedic Clinic in Los Angeles. "The non-contact ACL tear results when you're doing something that your brain hasn't planned or patterned, so you misstep. Or, unexpectedly, a blocker gets pushed into you with your foot planted."