ACL Injuries in Children and Teens

What are ACL injuries?

An ACL injury is when the anterior cruciate ligament (ACL) in the knee tears or sprains, affecting the knee’s stability and movement. ACL sprains and tears are among the most common knee injuries and can occur during childhood, adolescence and adulthood.

Athletes in sports like football, soccer and basketball are more likely to suffer from serious ACL injuries. This is because these sports involve running, jumping and quickly changing directions. Some of these injuries require surgical treatment.

About half of all ACL injuries occur in combination with other knee injuries, such as meniscus tears, anterior knee pain or damage to other structures of the knee such as cartilage and other ligaments.

Understanding the anatomy of the knee

Your child’s knee joint is at the intersection of three bones:

  • Thigh bone (femur)
  • Shinbone (tibia)
  • Kneecap (patella)

The kneecap is positioned in front of the knee joint to provide some protection for the four ligaments that connect the thighbone and shinbone and keep your child’s knee stable.

Collateral ligaments are on both sides of knee. The medial collateral ligament (MCL) is on the interior (the side next to the other leg). The lateral collateral ligament (LCL) is on the exterior of the knee. These ligaments control the sideways motion of the knee.

Cruciate ligaments in the knee form an “X” shape with the anterior cruciate ligament (ACL) in the front, and the posterior cruciate ligament (PCL) in the back. These ligaments control the back-and-forth motion of the knee. Additionally, the ACL provides stability to the knee and prevents the tibia from moving in front of the femur.

Fig. 1: Anatomy of the knee Fig. 1: Anatomy of the knee

Types of ACL injuries

ACL injuries are considered sprains and vary in severity.

  • ACL Sprain (Grade 1): The ligament is damaged and stretched but can keep the knee stable.  
  • Partial ACL Tear (Grade 2): The ACL stretches and becomes loose. Doctors often refer to this type of ACL injury as a partial tear of the ligament. This type of ACL tear is not common. 
  • Complete ACL Tear/Complete Ligament Tear (Grade 3): The ACL is completely torn – split into two pieces – making the knee unstable.  

Fig. 2: Complete ACL tear Fig. 2: Complete ACL tear

Causes of ACL injuries in children and teens

Various factors can cause ACL injuries including:

  • Stopping suddenly while running
  • Slowing down while running
  • Changing directions rapidly while running
  • Jumping or landing incorrectly
  • Contact injuries, such as a football tackle
  • Overuse of the leg from repetitive impact activity — such as jumping, running, twisting or pivoting

Are ACL tears common in children?

While ACL tears in children are not common – compared to all injuries children suffer – they occur more often in:

  • Youth who are especially active, and
  • Youth who take part in organized sports that involve a lot of running, jumping, twisting and pivoting.

Depending on the child’s age, they may be more likely to fracture a bone than tear their ACL.

Signs and symptoms of an ACL injury in child or teen

Signs and symptoms of an ACL injury may include:

  • Hear a popping sound
  • Feel as if their knee has given out from under them
  • Feel immediate pain
  • Experience swelling, especially for the first 24 hours after the injury
  • Be unable to continue playing immediately after the injury
  • Lose full range of motion
  • Experience joint tenderness
  • Feel discomfort while walking

Testing and diagnosis of ACL injury or ACL tear

If you suspect your child or teen has an ACL injury, an experienced orthopaedic physician should evaluate them.

At Children's Hospital of Philadelphia (CHOP), ACL injuries are treated by physicians from the Division of Orthopaedics and the Sports Medicine and Performance Center who specialize in diagnosing and treating bone and muscle injuries in children, teens and young adults.

Our expert doctors will perform a physical exam of your child, specifically addressing all structures of the injured knee, and comparing them to the non-injured knee.

We will assess your child’s pain level and ask questions about their medical history. Additionally, we may perform tests such as X-rays and MRIs. These tests help us understand your child’s condition and the severity of their injury.

Then, we will work with you and your child to develop an individualized treatment plan.

Treatments for ACL injury in children and teens

Treatment for your child’s ACL injury will depend on many factors, including your child’s age and development, the severity of the injury, and lifestyle goals long-term.

For example, an elite young athlete may require surgery to safely resume sports. Non-surgical treatment may be recommended for growing patients with less severe injuries.

Non-surgical options for treatment of ACL injuries

If the overall stability of your child’s knee is intact (i.e., an ACL sprain/Grade 1 injury) and your child still has open growth plates, orthopaedic physicians at CHOP will likely recommend non-surgical treatment. 

Growth plate Fig. 3: Non-surgical treatment may be recommended if your child has open growth plates and is not finished growing.

Options include:

  • Activity modification: This includes avoiding sports such as soccer and football, which involve "cutting" running activities that include jumping, pivoting, and twisting 
  • Knee brace: Doctors may recommend immobilizing the knee with a brace to help protect it from instability 
  • Physical therapy and rehabilitation: After swelling goes down, specific exercises can strengthen the leg muscles and help restore knee functionACL reconstruction surgery

Reconstruction surgery for a torn ACL

A torn ACL will not heal without surgery because there is no blood supply to this ligament. Standard treatment involves surgery to reconstruct the torn ALC. 

Learn more about having ACL surgery at Children’s Hospital of Philadelphia and why where you seek treatment matters.

Follow-up care and rehabilitation from ACL injury

Rehabilitation is vital for recovery after an ACL injury in children or teens — even if your child did not have surgery. Physical therapy will help your child regain strength and motion in their knee and leg.

If your child had surgery, rehabilitation will initially focus on returning motion to the knee and leg muscles. Next, your child will join a program to make the new ligament stronger by slowly adding more pressure to it. Finally, your child will take part in a customized program designed to optimize return to their chosen sport.

Regrowth of the ACL takes time. It’s important to help your child have realistic expectations about their recovery. It could take more than 6-9 months for an athlete to return to sports after surgery, depending on their training.

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