Sports Injuries: Anterior Cruciate Ligament (ACL) Injuries

Causes & Symptoms of ACL Injuries

The Anterior Cruciate Ligament (ACL) is a very important part of the knee, and is also one of the most commonly injured part of the body for sports players, especially those involved in intense contact sports such as Basketball and Soccer.

Anatomy of the Anterior Cruciate Ligament (ACL)

The ACL is one of the four ligaments found in the knee to provide stability for the knee joint. The knee joint allows the body to be in different position by bending and straightening. Being able to bend the knees is very important for many day-to-day activities like walking, running, standing and sitting.

The ACL is a crucial part of the knee joint, and it is found diagonally in the middle of the knee, forming an X on the knee joint with the posterior cruciate ligament (PCL), preventing the knee from sliding around, and also provides rotational stability to the knee, and when the feet pivots.

Anatomy of the knee
Image 1.1: Anatomy of the knee Source:

ACL injuries

There are several degrees of an ACL injury. Around 50% of ACL injuries comes with damages to other parts of the knee, such as the meniscus, the articular cartilage, as well as the other three ligaments.

A sprain refers to when a ligament is injured, with a chance of the fibres being stretched or even torn.

In Grade 1 sprains, the ligament is slightly stretched and only mildly damaged, with no fibres torn. The ligament can still help to keep the knee joint stable.

In Grade 2 sprains, the ligament is stretched to the point that it becomes loose, and partially torn.

In Grade 3 sprains, the ligament is completely torn into two pieces. The knee joint becomes completely unstable.

Extent of tear in the ACL
Image 2.1: Extent of tear in the ACL Source:

In most cases of ACL injuries, the sprain is a Grade 2 or 3, with the ACL being almost or completely torn. When the injuries occur, it is also common to hear or feel a “pop” in the knee. This results in the knee swelling, becoming unstable, and even too painful to stand.

What causes ACL injuries

ACL injuries are mainly due to sports, especially those that exerts a lot of stress on the knees, or involve sudden stops, changing of direction, jumping and landing, and pivoting. These sports include basketball, soccer, football and board sports like snowboarding and skiing.

ACL injuries can also arise from landing awkwardly after a jump.

In intense contact sports, the ACL can also be injured after receiving a direct collision to the knee.

Researches have also shown that female athletes have a higher risk of getting ACL injuries than male athletes. This could be due to several reasons. Female muscles in general are more elastic and this decreases the amount of protection that the hamstring muscles provides to the ACL. Hormonal changes that may occur during menses may also affect the elasticity. Female hamstrings also react slower than male’s, increasing the risk of ACL injuries during sport activities. Generally, female also have a wider pelvis compared to men, increasing the force that the ACL has to withstand, thus increasing the risk of injury.


Symptoms of ACL injuries

Symptoms of ACL injuries usually include:

  • Hearing a loud “popping” sound or experiencing a “popping” sensation in the knee
  • Rapid swelling in the knee joint
  • Severe pain and discomfort in the knees, resulting in not being able to continue activity, or even standing and walking
  • Difficulty in straightening the knee due to pain
  • Losing full range of motion

Immediately after the injury, do not attempt to continue, and in fact you may not even be able to do so.  Furthermore, returning to the activity may increase the risk of causing further damages to the knees.  See a doctor immediately when you have a chance because if the injury is left untreated, the pain and swelling may return, causing further aggravation.


Treatment & Prevention For ACL Injuries

Written by: Lim Jun Tian

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