Anterior Cruciate Ligament (ACL) Injury

What is an Anterior Cruciate Ligament Injury?

The anterior cruciate ligament (ACL) is a primary ligament in the knee. Partial or complete ACL Injury tears most often happen during sporting events such as basketball, football, soccer, baseball, tennis and other activities that require sudden movements. When the foot bears weight and force is applied to the outside of the knee, twisting and/or pivoting injuries can easily occur.  Sometimes a loud pop is heard and/or felt at the moment of injury, but not in every case.

What are the Symptoms of an Anterior Cruciate Ligament Injury?

The primary symptoms of an anterior cruciate ligament (ACL) injury are swelling and pain. The severity of the injury can often be gauged by the level of swelling. When the injury is severe, the area can swell within just a couple of hours. When less severe, it can occur over a period that exceeds 24 hours. The knee may feel weak, unstable and unable to bear weight.

Symptoms may also include

  • Stiffness
  • Muscles spasms
  • Excessive fluid build-up
  • Limited range of motion

Anterior Cruciate Ligament (ACL) Injury Causes

ACL injuries can occur in a number of ways, most of which are caused by sudden trauma or strain to the knee. Changing direction rapidly, for example, during sports like tennis or basketball, can injure the ACL. Suddenly stopping while running or walking at full speed, or slowing down while running, are also common ways to injure the ligament.

Sometimes the ACL is damaged by landing from a jump incorrectly, which can cause the ligament to be strained. Finally, if the knee is hit very hard from the side, for example, during a football tackle, the collision can damage the ACL.

Some studies have found that female athletes experience ACL injuries more frequently than men. It is not fully understood why this is, but it is theorized that it could be due to the differences in muscle tone, physical condition, pelvis and leg alignment between men and women. There is also a theory that the female hormone estrogen affects the properties of ligaments and it is this that causes a prevalence of ACL injuries in women.

How is an Anterior Cruciate Ligament Injury Treated?

Immobilization, rest, ice packs and compression are often enough to treat a minor ACL injury.

However, when the anterior cruciate ligament is torn, surgical repair might be required. It will take an MRI, an ultrasound, an x-ray and/or an arthroscopy (a flexible viewing tube) to determine the extent of the injury. When fluid build-up is excessive, the doctor may choose to drain it.

It is of the utmost importance to seek professional medical care after an ACL injury. Those who are injured are more susceptible to developing osteoarthritis, even with surgery.  A brace may be necessary for stabilization, and crutches may be required to prevent pressure on the knee. Physical therapy can restore full range of motion and strength. When surgery is required, even with rehabilitative therapy, it can take up to a year to fully heal enough to resume sporting activities.

Anterior Cruciate Ligament (ACL) Injury Prevention

Athletes and amateur sports players, particularly those in sports which involve movements that can commonly cause ACL injuries, may try to modify their movements in order to minimize the risk of damaging their anterior cruciate ligament. They could consult a physical therapist, trainer or sports medicine specialist for advice on their form.

It is also often possible for physical therapists and doctors to identify weak muscles areas which might increase the risk of ACL injuries. For example, an athlete with weak hips is more likely to land in a knock-kneed position, which could damage the ACL. The athlete could then focus on training exercises which will strengthen the hips and reduce the risk of ACL injury.

Young athletes will benefit greatly from undergoing training programs and exercises which help them to learn correct form, which minimizes the risk of ACL injury. The older we get, the more likely we are to develop certain habits, and it is much easier for adolescents to learn good form than it is to attempt to change bad form years down the line.

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Last Reviewed:
September 11, 2016
Last Updated:
November 08, 2017