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ACL Injuries: Causes, Symptoms and Treatments

The knee joint is formed by the shinbone (tibia), thighbone (femur) and kneecap (patella). The kneecap is located in front of the joint and acts as its protection. The four primary ligaments that connect these bones and keep the knee stable are as follows:

  • Lateral collateral ligament (LCL) – located along the outside of the knee and prevents it from bending out
  • Medial collateral ligament (MCL) – located along the inside of the knee and prevents it from bending in
  • Posterior cruciate ligament (PCL) – functions in tandem with the ACL and prevents the shinbone from sliding under the thighbone
  • Anterior cruciate ligament (ACL) – functions in tandem with the PCL; they cross each other, with the PCL in the back and the ACL in the front. The ACL is located in the middle of the knee and prevents the shinbone from sliding in front of the thighbone. Both the PCL and ACL are crucial in controlling the motion of the knee.

An ACL injury occurs when the anterior cruciate ligament in the knee tears or is overstretched. The injury can also be accompanied by damage to other parts of the knee, such as the meniscus, the articular cartilage or the other ligaments. The severity of an ACL injury is divided into three types of sprains:

  • Grade 1 Sprains – the ligament is stretched slightly, but still capable of keeping the knee joint stable. The damage is considered to be mild.
  • Grade 2 Sprains – the ligament is stretched until it becomes loose. The damage is considered a partial tear.
  • Grade 3 Sprains – the ligament has been split, causing the knee joint to become unstable. The damage is considered a complete tear.

When an ACL injury occurs, it is essential for the patient to consult a specialist and begin the treatment process as soon as possible.

Causes of ACL Injury

Female athletes are more at risk of developing an ACL injury than are male athletes. This is due to differences in the effects of estrogen on ligaments, muscular strength and physical conditioning. The injury is also common among football players, soccer players, basketball players and skiers. A person can injure his or her ACL in several different ways:

  • By overextending the knee joint
  • By abruptly halting or changing direction while jumping or running
  • By experiencing a collision or direct contact on the side of the knee, such as in a soccer tackle
  • By landing incorrectly after a jump
  • By slowing down during a run

Symptoms of ACL injury

Typical symptoms of ACL injury include:

  • A “popping” noise and the knee giving out when the injury occurs
  • Swelling within 24 hours of the injury
  • Pain that intensifies when putting weight on the injured leg
  • Discomfort while walking
  • Joint line becoming tender
  • Loss of movement

If any of these symptoms occur, do not return to sports. The knee is still unstable and further damage to it can be caused; consult a specialist as soon as possible.  

Diagnosis of an ACL injury

An ACL injury can be diagnosed through a variety of methods:

  • A physical examination The patient’s symptoms and medical history will be evaluated. The doctor will compare the patient’s injured knee with the non-injured knee, checking all the different structures. Most ligament injuries can be diagnosed through this method.
  • X-Rays An x-ray can show the association between an injury and a broken bone. However, an x-ray will not show the damage done to the anterior cruciate ligament.
  • Magnetic Resonance Imaging (MRI) scan Creates better images of the anterior cruciate ligament and other soft tissues. However, in most cases, an MRI scan is not necessary for the diagnosis of a torn ACL.

Treatment of an ACL injury

There are two types of ACL treatments: surgical and non-surgical. To learn more about both types of treatments, including arthroscopic surgery, click here.

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  1. Anterior Cruciate Ligament (ACL) Injury. Available from Accessed on August 11, 2016.
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  3. Anterior Cruciate Ligament (ACL) Injuries and Surgery. Available from Accessed on August 11, 2016.

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