If you're at all a sports fan, or an athlete yourself, you've probably heard of the anterior cruciate ligament.

It's commonly injured.

Now a new study shows what happens to NFL players who are sidelined by their acl's, and it's not good news for players or fans and the owners.

Now, a ligament is a strong piece of connective tissue that connects bone to bone across a joint. The anterior cruciate ligament crosses with the posterior cruciate ligament in the center of the knee.

They control the backward and forward motion of the knee. The ACL in particular restrains excessive forward motion of the knee as well as the inward twisting or rotation of the knee.

In fact, the ACL is frequently injured in severe twisting injuries of the knee or with a sudden stop.

This new research in the American Journal of Sports Medicine looking specifically at ACL injuries in NFL players found those who suffer one of these injuries will likely never be the same player again.

Essentially, total yards and touchdowns were markedly diminished when they returned after surgery.

Dr. James Gladstone, an orthopedic surgeon at Mt. Sinai Medical Center, says, "They're only playing at approximately 2/3rds of the level they were playing at before the injury."

Dr. James Carey, the study author out of Vanderbilt University, says, "It's the first time anyone has used player performance and their statistics to look at the outcomes of a surgical procedure."

Perhaps the most concerning stat is that one fifth--21 percent--of the injured players never played another NFL game.

"The predominant thinking when 31 head NFL team physicians were interviewed, is that 90 to 100 percent of players, presuming not borderline talent, return to the NFL," states Dr. Carey.

Of those who did return, it took 9 to to 12 months to get back on the field.

"This study gives us pause and says even in the best case scenarios these are players who are going to work their butts off doing rehab 8 hours a day to get back to playing and even then a fifth of them, 20 percent aren't getting back to playing," Dr. Gladstone adds.

Interestingly, those who get ACL injuries are more likely to be high-performance players.

"They have frequent accelerations, decelerations, twisting, cutting maneuvers, that puts them at the highest risk," according to Dr. Carey.

They're more likely to be injured because they compete in more plays per game, carry the ball longer on each play, and attract more defensive attention.

"The biggest problem with an ACL injury is that once it's torn there is no way that it's going to heal or be repaired, except with surgery," says Dr. Gladstone.

But those great players end up less great after that surgery.
It's believed players don't get back to where they were because of one or more factors, including knee pain, stiffness, loss of strength, deconditioning and reduced proprioception, which is the sense of knowing where your leg is.

Also, ACL reconstruction does not perfectly recreate the complex anatomy and composition of a player's ACL before injury.

"They should have reasonable expectations for what they can expect their knee to do and how they can contribute to the team in the future and I think it's important to the fans and the team owners to similarly have those expectations that are realistic," Dr. Carey points out.

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