Anterior cruciate ligament avulsion fracture: An injury that cannot be underestimated in young people

An anterior cruciate ligament (ACL) injury occurs when a small bone fragment at the tibial plateau—where the ACL attaches—is avulsed from its anatomical position following trauma. Instead of the ligament tearing across, the traumatic force pulls off the bone attachment site of the ligament.

Simply put, the ligament is like a hammock strung between two nails on a wall. When one nail is pulled out, the hammock loses its tension and can no longer perform its original function. Treatment in this case is not about "patching the hammock," but rather returning the nail to its proper position so the system functions normally again.

Essentially, an ACL avulsion fracture is a type of intra-articular fracture of the knee joint.

Why is this injury common in adolescents?

In young individuals, especially during the bone-growing phase, the bony insertion site structure is usually weaker than the ligament. Therefore, when there is a strong twisting force or trauma to the knee, instead of the ligament tearing, the bone where the ligament attaches is avulsed.

This condition usually occurs following:

• Sports accidents
• Falls during physical activities
• Traffic accidents
• Sudden knee-twisting injuries

Patients typically experience severe knee pain, rapid swelling after the injury, and difficulty walking.

Is an ACL avulsion fracture dangerous?

It is noteworthy that if the injury is not diagnosed and treated properly, the ACL will lose its tension and can no longer ensure the stability of the knee joint.

Consequences may lead to:

• Knee laxity
• Knee joint instability
• Limited mobility
• Increased risk of meniscus and articular cartilage injury in the long term

Since this is a bone injury, normal bone healing typically requires about 6 weeks after the bone fragment is reduced to its proper anatomical position.

Classification of ACL avulsion fractures

According to the Meyer and McKeever classification, the injury is divided into 4 grades:

• Grade I – Non-displaced: The bone fragment is avulsed but remains close to its original position, and the knee joint is relatively stable.
• Grade II – Partially displaced: The anterior part of the bone fragment is elevated while the posterior part remains attached, creating a "hinge-like" appearance.
• Grade III – Completely displaced: The bone fragment is completely avulsed from the tibial plateau and displaced upward.
• Grade IV – Completely displaced with rotation/flipping: The bone fragment is completely avulsed, may be flipped upside down, detached, or complexly fractured.

Classification is crucial in selecting the treatment method.

When is surgery necessary?

For Grade I injuries or certain Grade II cases, conservative treatment with immobilization may be considered if imaging shows the bone fragment has returned to an appropriate position.

However, in cases with displacement that causes a loss of ACL tension, surgery is a necessary indication to restore knee joint stability.

Previously, open reduction and screw fixation were commonly used and yielded good results. Nowadays, along with the development of arthroscopic techniques, the majority of ACL avulsion fractures can be treated arthroscopically.

Advantages of this method include:

• Minimally invasive
• Small surgical scars
• Clear visualization of intra-articular injuries
• Better support for rehabilitation
• Enhanced postoperative aesthetics
• Timely treatment helps preserve knee joint function

An ACL avulsion fracture is an injury that can recover well if detected early and treated properly. Conversely, delaying treatment can lead to prolonged knee instability and affect future motor function.

If you experience a knee injury after physical activity, an accident, or have a sensation of knee laxity, prolonged pain, and swelling after trauma, you should consult Dr. Vu Anh - Department of Orthopedics & Sports Medicine early for an accurate assessment of the injury severity and to select the appropriate treatment direction.