What is an ACL?

Simply put, an anterior cruciate ligament (ACL) connects the bottom of the femur (thighbone) to the top of the tibia (shinbone). It is one of four ligaments in the knee and is responsible for stability, forward movement of the lower leg and preventing rotational stress. Not only is the ACL the weakest of the four ligaments in the knee, too much stress can cause it to tear.

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How does the ACL get injured?

Direct contact ACL injuries occur from an on-field or on-court collision. Non-contact ACL injuries are usually the result of a quick pivot, unbalanced landing or acceleration of speed followed by a sudden stop. Sometimes, the non-contact ACL injury can be exacerbated by overuse, when an athlete continues to play one sport year round without a break. Experts are most concerned about the rising number of non-contact ACL injuries, which account for nearly 70 percent of all ACL injuries.
Who gets an ACL injury?

Anyone can get an ACL injury, but the most susceptible are those involved in sports that require pivoting, jumping, decelerating and turning quickly, such as skiing, basketball, football, lacrosse, volleyball, cheerleading, soccer and gymnastics.

Females are at greater risk than males. The American Academy of Orthopaedic Surgeons (AAOS) reports that female athletes are up to 10 times more likely to sustain an ACL tear than their male counterparts. This is because higher levels of estrogen in women actually weaken the tendons by relaxing the fibers, making them more susceptible to tears. Since girls typically have wider hips than boys, there is a smaller notch for the ligament to connect to the femur, which restricts movement. Girls are also more likely to land on their feet with knees straight, as opposed to bent, which increases pressure on the joints. With more girls playing sports since the inception of Title IX in 1972, there has been at least a 10-fold increase in the number of injuries sustained by females.

What are the symptoms of an ACL injury?

Many patients are only too aware of their injury. There is usually intense pain, a telltale pop or snap, a loose feeling in the joint and an inability to put weight on the affected limb. However, there are instances in which the extent of the injury is less severe. Some ball players have been known to play with a damaged ACL, but that is an exceptional situation. Any lack of stability in the knee should be followed up with an MRI to assess damage. The risk of permanent injury, arthritis and total knee replacement is too great not to check for signs of a torn ligament.

How prevalent is it?

ACL injuries are extremely common among both professional and amateur athletes.

About 400,000 people in the U.S. are treated for ACL injuries every year. Medical professionals nationwide are seeing a significant uptick in the number of ACL injuries every year. Physicians in Philadelphia documented a 400 percent increase in ACL patients in a 10-year time period. From 2009 to 2013, the number of MOR patients with ACL injuries doubled. The number of ACL injuries in young people under age 25 tripled in that same five-year period. That’s why Midwest Orthopaedics at Rush (MOR) physicians are concerned about what they call an epidemic of ACL injuries.

With more emphasis on competitive sports and more young people engaged in these activities year-round, the numbers are going up.

To counter these accelerated rates of injury and to reduce stress on the joints, more cross training should be emphasized. Longer breaks between activities and exercises to improve balance and core strength around the knee joints can further lessen the likelihood of an ACL tear in people involved in rigorous competition.


Midwest Orthopaedics


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