ACL Tear: Causes, Symptoms, and Treatment

Before I get into answering the question, “What is an ACL tear?” I’ll start with an explanation the anterior cruciate ligament (ACL) itself. The ACL (also known as the anterior cruciate ligament) is one of the four main ligaments in the knee. The ACL is located within the knee joint. BraceAbility offers treatment options for many knee injuries, including ACL tears.

See the article “Anterior Cruciate Ligament” for a more detailed explanation as to its location in the knee or watch this video detailing the anatomy of the knee:

ACL Ligament

The ACL’s main function is to stabilize the knee when the leg is extended or if the surrounding muscles are relaxed. More specifically, the ACL ligament prevents the lower leg from extending too far relative to the thigh bone and it limits how far the knee can rotate. In doing so, the ACL also helps to limit stress on the knee joint.

The ACL is an important ligament, but it is not a vital one. If an individual’s related muscles are strong, he or she can enjoy an active lifestyle without it. Doing so does, however, increase the risk of other injuries to the knee and restricts one’s ability to participate in sports that involve quick, sudden movements and/or twisting.

Symptoms of ACL Tear

When one tears an ACL, there are typically four main ACL tear symptoms:

• Popping sound or sensation
• Pain (moderate to severe) when bending knee
• Swelling
• Instability of the knee

The ACL tear swelling typically occurs within several hours of the injury. The referenced instability of the knee may include buckling, locking or giving way during movement or when one is simply putting weight on the knee. The severity of the ACL tear pain and other symptoms will depend upon whether a complete ACL tear or a partial ACL tear occurred.

Regardless of the severity of the pain, if an athlete thinks he or she might have torn the ACL, the individual should stop playing immediately and seek medical attention. Ignoring the symptoms of an ACL tear and continuing the athletic activity can cause major cartilage damage that can increase one’s risk of osteoarthritis down the road.

It should also be noted that ACL injuries often coincide with other knee injuries. For instance, one might experience an ACL and meniscus tear at the same time. In fact, there is a term for when one tears the ACL, the medial collateral ligament (MCL) and the meniscus at the same time: O’Donohughue’s triad, also known as the unhappy or terrible triad.

A medical professional can conduct an ACL tear test to determine whether an ACL tear did indeed occur; an ACL tear MRI can be used to confirm the injury and check for additional damage to the knee. If an ACL Tear did occur, an ACL tear treatment brace may be necessary.

Causes of a Tear in ACL

ACL tears can occur due to a number of things, but generally speaking, most such injuries fall into the category either of sports injury, trauma (e.g., hitting the knee during a car crash) or a fall for someone above the age of 40. Aging causes wear and tear to the knee joint that leaves its ligaments more vulnerable to injury.

Sports injury is the most common culprit for an ACL tear. Complete or minor tears to the ACL typically occur during non-contact motions. The most common of these is when one bends the knee too far back (hyperextending it) or if the knee goes too far to the side. This might occur when one pivots or cuts during sports like basketball or soccer.

A sudden change in motion paired with sudden deceleration can also result in an ACL rupture, as can an abrupt stop with an extended leg (think a baseball slide into second base or straight-knee landings of gymnastics dismounts).

An ACL tear can also occur when one is in a stable position with both feet planted solidly on the floor if the knee is hit directly from the front, as might occur in wrestling or football.

The theme across all of these sports-related causes of ACL injuries is that they involve sudden changes in either the direction of motion or a sudden halt to motion itself.

Risk Factors

People can choose what sports they take part in, but aging is not something one can avoid. Another uncontrollable risk factor for an ACL tear is one’s gender. Females are far more likely to tear the ACL ligament than males.  

In fact, NCAA analysis of ACL tear statistics shows women are two to eight times more likely to tear their ACL than men. Other studies have yielded variations of these figures, but the conclusion remains the same: women are significantly more likely to tear their ACL than men. The reason for this is multifaceted, involving physical, neuromuscular and hormone differences between the sexes.

One major difference is that women typically have strength imbalance in the muscles of their thighs, contrary to men. Specifically, their quadriceps (front thigh muscles) is usually stronger than their hamstrings (muscles at the back of the thigh). This is problematic as the hamstrings are the muscles that are supposed to prevent the shin from moving too far forward.

Also, men have greater ligament strength than women. In addition, women have less hip and knee flexion than males. This, along with the quadriceps/hamstring imbalance, equates to them having less neuromuscular coordination and control when landing a jump which can result in women more often landing in a compromising position.

 Another physical difference is that both the ACL ligament itself and the joint through which it passes are typically smaller in woman than men, making it more vulnerable to injury. Further, women usually have wider hips and shorter femurs than men, which can result in stress being putting on ligaments and joints rather than muscles.

Hormones also come into play in making women more prone to a partial tear of ACL or a complete tear of ACL. More relaxed estrogen receptors during menstruation can make one more prone to injury, as can the hormone relaxin that (you guessed it) relaxes or loosens the ligaments. This hormone is released when one is pregnant.

ACL Tear Repair

Regardless of one’s sex, treatment of an ACL tear is largely the same. If one has “just” an ACL partial tear, a doctor might recommend repairing the ACL tear without surgery via physical therapy to strengthen the muscles associated with the knee so that they can compensate for the weakened ligament. But as previously mentioned this leaves one at risk for additional knee injuries, especially if the athlete’s sport involves some of the previously detailed high-risk motions.

For such instances as well as in the case of an ACL complete tear, reconstructive ACL tear surgery is necessary. Note I did not say rehabilitative. Because there is no blood flow to the ACL ligament, the body is not able to naturally repair damage to this connective tissue. Thus, ligaments from another part of your body, namely the hamstring or the patella tendon, or cadaverous tissue must be used to repair an ACL ligament tear.

A surgeon will wait several weeks after the injury to allow swelling to go down before operating. During this lag time, rest, ice, compression and elevation of the knee will be needed to get the inflammation under control.

Following surgery, one will be advised to wear a post-operation knee brace and to use crutches for around a month. After the initial healing period, one will have to undergo a lengthy rehab process ranging from six months to a year.

For much of this recovery period, one will likely be unable to engage in sports, and when an athlete is cleared for athletic activity, he or she will likely be advised to wear an ACL knee brace for some time, especially if the sport involves person-to-person contact.

ACL Tear Prevention

Those involved in sports that are high-risk for an injury can engage in workouts to improve the neuromuscular factors involved with proprioception as well as to improve one’s balance, form and muscle strength with the ultimate goal of preventing an ACL injury or re-injury.