According to the American Academy of Orthopaedic Surgeons, more than 100,000 Americans tear their anterior cruciate ligament (ACL) every year.

Ligament tears and other knee injuries have long been a point of contention in the determination of value in the world of fantasy football, and they have come to the forefront again this offseason.

Several valuable runners, including Ronnie Brown, Kevin Jones and Deuce McAllister, will attempt to return to their previous form after reconstructive ACL procedures.

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Ronnie Brown's ACL injury makes him a risk-reward selection in 2008 fantasy drafts.

Another running back, Cadillac Williams, will look to come back from a torn patella tendon that some fear could threaten his pro football career.

In an effort to better educate ourselves on the nature of the injury that ended the careers of former NFL greats such as Red Grange and Gayle Sayers, we first have to look at the more recent past to see how this sort of physical damage has affected a player's statistics.

Since 1998, several prominent backs have sustained severe knee injuries and failed to meet statistical expectations the next season. Terrell Davis, who suffered a torn ACL in 1999, was never the same after his ACL operation. In fact, he rushed for 282 yards in 2000 and failed to rush for a combined 1,000 yards in what would be the final two seasons of his career.

Jamal Anderson was a superstar fantasy running back in his time with the Atlanta Falcons, but he also sustained a torn ACL in 1999. The former "Dirty Bird" came back to rush for 1,024 yards and six touchdowns in 2000, but that was 822 fewer yards and eight fewer touchdowns than he recorded in the season before he suffered the ailment.

Anderson sustained another torn ACL in 2001 which would ultimately force him out of football.

Edgerrin James also tore an ACL during the 2001 season, and his 2002 numbers (989 rushing yards, two rushing TDs) left much to be desired compared to his totals the season before he was hurt (1,709 rushing yards, 13 rushing TDs). James did re-emerge into one of the best backs in fantasy football in 2003 and in seasons beyond, but it seems evident that his reconstructed ACL was to blame for his lack of 2002 statistics.

One of the most gruesome and remembered knee injuries in recent seasons happened to Willis McGahee, who tore three of the four ligaments (ACL, MCL, PCL) that hold the knee in place in the 2003 Fiesta Bowl against Ohio State. Rather than attempt to come back too soon after what was a serious reconstructive procedure on the knee, McGahee was forced to sit out the entire 2003 NFL season with the Buffalo Bills.

There are a few exceptions to this trend, as Jamal Lewis and McAllister were both able to make an impact the season after a reconstructive knee procedure.

Lewis ripped up his knee in 2001 as a member of the Baltimore Ravens and missed the entire season, but he still rushed for an impressive 1,327 yards and six touchdowns in 2002. He would go on to rush for an incredible 2,066 yards and 14 touchdowns in 2003.

McAllister sustained a similar ailment with New Orleans during the 2005 season, but he was able to record 1,057 rushing yards and 10 touchdowns in 2006.

Despite these two examples of players that were able to find success soon after ACL injuries, most of the backs who fall prey to a torn ACL aren't the same right away.

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In fact, a study in the December 2006 issue of The American Journal of Sports Medicine concluded that players with ACL ailments returned to the field with far less statistical success compared to the season before the ligament was damaged.

The report, written by Dr. James L. Carey, was a collection of data on ACL injuries to both running backs and wide receivers from 1998-2002. Carey and his colleagues devised a "power rating" for each player in every season, and was defined as a sum of their total yards and touchdowns.

This group of injured players was compared to a group of players who played in 2000 and did not sustain an ACL injury. The rating compared the three seasons prior to the player's ACL injury (when the player was at 100 percent) to the three seasons after the player's ACL injury.

Of the 33 injured players in the report, 21 percent (seven of 33) never even returned to play in another regular-season contest in the NFL. The 79 percent of players that did return in nine to 12 months saw their numbers fall by one-third based on the rating. This decline was significant compared to the 146 players in the control group, so it was evident that a torn or damaged ACL caused a statistical downfall.

So what do these facts and statistics mean for the value of Brown, Jones, McAllister and Williams for the 2008 season?

Well, it means that fantasy footballers need to temper their expectations, prepare for less and hope for more. In the case of Brown, who is the most valuable back of the four, owners shouldn't expect him to produce at the rate of last season.

Based on the numbers from his seven starts in 2007, Brown would have finished with an impressive 89 receptions, 2,265 all-purpose yards and 11 total touchdowns in 16 contests.

Casey's research suggests Brown won't come close to those totals in 2008, and the emergence of veteran Ricky Williams makes him even more of a risk.

Jones and McAllister, who have both sustained two serious injuries in the past three years, will find it harder to find on-field success. One season after he suffered an injured foot that cost him the start of 2007, Jones sustained a torn ACL in late December. While he said he's two weeks ahead in his recovery from the reconstructive surgery, chances are Jones won't be the same back in 2008 (if a team takes a chance on him).

McAllister sustained his second torn ACL in three seasons last September and underwent an operation to repair the damage later in the month. The veteran out of Mississippi hopes to be available for the Saints' May 29 minicamp, and he does have an advantage in that his knee surgery was performed much earlier than Brown or Jones. However, it's hard to expect much from a 29-year-old running back with two reconstructed knees.

The back with the most severe damage, Williams, might start the season on the Physically Unable to Perform (PUP) list so he has more time to recover. With Warrick Dunn now in Tampa Bay, Williams won't even be taken in most drafts.

Whatever the scenario, fantasy footballers can bet that Williams, much like Brown, Jones and McAllister, won't be the same for all or part of 2008.

That should be remembered when's it's time to draft.

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