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Column: The ACL: What is it and why do we injure it so frequently?

Trenton D. Salo • Jan 13, 2017 at 12:13 AM

We’ve seen it before — an unfortunate situation where an athlete lands awkwardly and falls to the ground grabbing their knee. The first thought that typically occurs among those watching is, “uh-oh, I hope it isn’t an ACL injury!” What exactly is the ACL though? And why is it injured so frequently?

The knee joint is made up of the thighbone (femur) and the shinbone (tibia). Connecting these two bones of the knee are four primary ligaments; one of which is called the anterior cruciate ligament (ACL). The ACL attaches on a diagonal, which allows it to withstand high stress during lateral cutting and rotational activity. If these dynamic movements are not well controlled with our muscles the ligament can easily become overloaded.

There are over 200,000 ACL injuries each year in the United States. While the likelihood of ACL injury is low in straightforward activities, such as jogging, the risk of ACL injury increases tremendously in multi-directional and cutting sports, such as basketball and soccer.

ACL injuries can be classified into ‘contact’ and ‘non-contact’ injuries. Contact injuries occur when a player lands on another athlete’s knee, causing the knee to crash inward. Non-contact injuries occur during a cutting or landing movement where the force of the movement is greater than the athlete’s ability to absorb the force.

Who is at the greatest risk? Research suggests female athletes involved in multi-directional sports are at the greater risk for an ACL injury (especially non-contact injuries) compared to their male counterparts. While the cause of this increased risk is complex and likely due to multiple factors, including bony anatomy and hormones, male versus female differences in leg strength is often cited as the primary reason.

ACL injuries can be diagnosed by an injury history and physical examination. A MRI scan can also be used to confirm an ACL injury and determine the involvement of other structures of the knee i.e. meniscus, medial collateral ligament (MCL), lateral collateral ligament (LCL), and posterior crutiate ligament (PCL).

If the ACL is torn, surgery to repair the tear is commonly recommended. Research is starting to emerge which suggests not everyone needs to immediately undergo ACL surgery. However, if an athlete is expecting to return to high-level multi-directional competitive sports, surgery is likely the best choice. If an athlete does not wish to return to multi-directional activities and the reported stability of the athlete’s knee isn’t significantly altered, a conservative non-surgical approach may be an option.

Regardless of whether a conservative or surgical approach is chosen, proper rehabilitation after ACL injury is crucial. During the early stages of ACL rehab, it is important to normalize knee swelling and range of motion. Later stages of rehabilitation focus on regaining knee strength and power, and increasing the stability of the knee with various balance exercises and sport-specific movements.

While complete prevention is impossible, the risk of an ACL injury can be significantly reduced if an athlete participates in a proper training program. The good news is these training programs also result in improved athletic performance!

Whether you’re an athlete looking to improve your performance and reduce your risk of injury, or an athlete returning to sport after ACL injury/surgery, it is important to find a physical therapist, athletic trainer, or movement professional who understands the dynamic demands of your knee.

— By Trenton D. Salo — Doctor of Physical Therapy, Certified Strength and Conditioning Specialist and 
Certified Exercise Physiologist

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