Carlos Rogers was expected to be one of the key players in the Redskins' defense this year. The 6-0, 194-pound third-year cornerback out of Auburn was a first-round draft pick by the Redskins.

In the Redskins' 34-3 win over Detroit at FedExField on Week 5, Rogers picked off a Jon Kitna pass and sprinted 61 yards to the end zone.

It was his signature play for the team.

That's because three weeks later at New England, Rogers started at cornerback and made one tackle before leaving the game with a knee injury.

A week later, Rogers went on the injured reserve list. His type of setback is a potential threat for all athletes, NFL players included.

When Rogers went down at New England with a torn ACL, or anterior cruciate ligament, it marked the third such devastating injury for the Redskins in the past year. Steven Harris and Nehemiah Broughton earlier had suffered torn ACLs.

"Injuries to the anterior cruciate ligament are among the most common of all sports-related knee injuries," says Raymond Thal, M.D., who is in his eighth season as an orthopedic specialists on the Redskins' medical staff.

It is estimated that each year in the United States between 100,000 and 200,000 people sustain a ruptured or torn ACL.

A ligament is made of tough fibrous material and functions to control excessive joint motion. The knee contains four ligaments that connect the femur (thigh bone) to the tibia (shin bone).

"These ligaments hold the bones in proper alignment and help control the way the knee moves," points out Dr. Thal, of Reston Hospital Center and Town Center Orthopaedic Associates.

There are two ligaments on the sides of the knee, the medial collateral ligament (MCL) and the lateral collateral ligament (LCL).

The other two ligaments, called the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL), cross each other in the middle of the knee.

The ACL controls movement of the lower leg bone in several ways. It provides front-to-back stability as well as rotational stability to the knee. It also keeps the knee from extending beyond its normal range of motion.

"Obviously," according to Dr. Thal, "these are extremely important functions, particularly for athletes."

An ACL tear most often occurs during sporting activities when an athlete suddenly pivots, causing excessive rotational forces on the ligament. A direct blow to the knee can also cause an injury to the ACL.

Often a pop is felt or heard in the knee. Over the next several hours, the knee becomes very swollen. It is usually difficult to bear weight on the injured leg and the knee may give way or feel unstable.

Explains Dr. Thal: "A completely torn ACL does not heal. This causes the knee to become unstable, which can make sudden, pivoting movements difficult. It may make the knee more prone to developing arthritis and cartilage tears."

When an ACL tear is suspected, a physician can assess the stability of the knee by specific maneuvers and tests including X-rays and MRI scans.

Experts Emphasize With a Tear, There's No 'Repair'

Many factors must be considered when determining the appropriate treatment for ACL tears. The patient's age, activity level and expectations are factors. So is the presence of associated injuries, such as cartilage tears, and the degree of knee instability.

Says Dr. Raymond Thal, who specializes in sports medicine and arthroscopic surgery: "Less active individuals may choose non-surgical rehabilitation. This usually requires a change in activities, including avoiding sports that require cutting, pivoting and jumping. Nonetheless, surgery is usually required for young, active individuals."

ACL surgery is commonly referred to as an ACL repair. Unfortunately, a torn ACL cannot be "repaired." Simply sewing the ligament together is rarely successful.

Rather, an ACL reconstruction is performed by replacing the torn ligament with healthy tissue called an ACL graft.

Several excellent graft options are commonly used for ACL reconstruction. Typically used are tendons from around the knee-most commonly the patella tendon or hamstring tendons or allograft (donor) tissue.

ACL reconstruction is usually not performed until several weeks after the injury. Studies have shown improved results when ACL reconstruction surgery is delayed several weeks from the time of injury. This time allows the knee swelling to decrease and range of motion to improve.

Significant rehabilitation is required after ACL reconstruction. This is an important aspect of care for a torn ACL that significantly impacts the results of ACL reconstruction.

"Most patients experience full recovery and can return to their previous activities, including professional level sports," maintains Dr. Thal.