By: Sigrid F. Wolf, MD, FAAP
The anterior cruciate ligament (ACL) is one of the four major ligaments that stabilize the knee joint; ligaments are tough, non-stretchable fibers that hold bones together.
The ACL—along with the posterior cruciate ligament (PCL), medial collateral ligament (MCL), lateral collateral ligament (LCL), and menisci (cartilage pads) —help keep the knee stable from sliding, rotating, and hyperextending during running, jumping, and landing.
What are the symptoms of a torn ACL?
ACL tears can occur when you suddenly stop while running, change direction quickly, take off for a jump or land from a jump awkwardly, or twist your knee.
An ACL tear is often associated with the following symptoms:
Sudden knee pain
A "popping" in the knee at time of injury
Knee swelling within 24 hours of injury
Limited knee movement
A feeling of looseness in the knee or a sensation that the knee is unstable or gives out
Some children with an ACL tear may have little to no swelling or pain and still be able to walk or run even though they have a serious injury. When the ACL is torn, it is common to also have injuries to the MCL and meniscus. The symptoms of an MCL sprain or torn meniscus may be more pronounced than the symptoms from an ACL tear alone.
Are some children at a greater risk of injury?
As pre-teens enter into puberty and grow taller and heavier, their risk of ACL injury increases – beginning at age 12 for girls, and age 14 for boys. Girls are at higher risk of ACL injury because after puberty, as their body size increases, girls do usually not develop more muscle power.
In fact, female athletes between 15 and 20 years old account for the largest number of ACL injuries. At the high school level, girls soccer has the most ACL injuries, followed by boys football, girls basketball, girls gymnastics, and boys and girls lacrosse. Among high school and college athletes, females have two to six times higher ACL injury rates than males in similar sports. Compared with boys, girls are more likely to have surgery and less likely to return to sports after an ACL injury.
When should you seek medical care?
Seek medical care if your child has a knee injury with a pop, swelling, difficulty with knee movement, or instability in the knee. Medical attention may also be necessary if your child is having trouble running, jumping, or changing directions.
After a Sports Injury: When to See the Doctor.
What tests might a child receive for an ACL injury?
Initially, doctors examine your child's injured knee and may order x-rays. The physical examination of the knee may reveal the ACL is loose or torn. Magnetic resonance imaging (MRI) is the best test to confirm a suspected ACL tear and to check for other injuries such as a torn meniscus.
In younger children whose bones are still growing, an x-ray may reveal that a suspected ACL injury is a bone fracture at the attachment site of the ACL. For best recovery, this type of fracture should be identified and treated within 7 to 10 days of the injury.
How are ACL tears are treated?
Treatment for ACL tears depends on the athlete's age and sport.
Non-surgical treatment may include modifying the athlete's sports and physical activities, rehabilitation exercises, and wearing a
Surgical treatment creates a new ACL from a tendon in the athlete's knee. Surgery is ideally done after the athlete has recovered from the initial injury and regained knee range of motion and leg strength. If the knee is still swollen, stiff, or weak at the time of surgery, then the recovery may take longer. Overall, ACL surgery is about 90% successful in restoring knee stability and patient satisfaction, and athletes typically return to their sports within 6-9 months after surgery.
Young athletes may choose to delay surgery until their bones are finished growing to avoid the risk of growth plate injury from the surgery. New surgeries are being developed that do not disrupt the growth plate, and thus can be safely performed in an athlete who is still growing. Parents who are considering surgery for their child should seek out a pediatric orthopedic surgeon with sports medicine training.
What are the effects of an ACL tear on young athletes?
The effects of an ACL tear can be long-lasting. Injured athletes who become distanced from their sport and its social network can experience depression, and time away from school for treatments can impact academic performance. In addition, children and teens with an ACL injury are up to 10 times more likely to develop early
arthritis—typically about 15 years after the injury—no matter what treatment they receive. This is important, because it means athletes who suffer an ACL tear at age 13 are likely to face chronic pain in their 20s and 30s. And while any child can tear their ACL, those with a prior ACL injury have a 25-35% increased risk of having a second ACL tear.
How to prevent ACL tears and re-tears:
Research demonstrates that specific types of physical training can reduce the risk of ACL injury as much as 72%, especially in teen girls.
ACL injury prevention programs use neuromuscular training to improve running, jumping, and landing techniques to strengthen the hips, core (trunk), and hamstrings. Research has shown that these programs not only reduce the risk of ACL tears, but can also reduce
ankle sprains and
patellofemoral knee pain. Research has not found knee braces to be effective at preventing ACL tears.
ACL injury prevention program examples:
About Dr. Wolf:
Sigrid F. Wolf, MD, FAAP is a pediatric sports medicine fellow at Northwestern University and Ann & Robert H. Lurie Children's Hospital of Chicago. She has served as a team physician for Northwestern University, De La Salle Institute, and Moody Bible Institute. She has provided medical coverage for several marathons and other mass sporting events. Within the American Academy of Pediatrics, she is a member of the Council on Sports Medicine and Fitness (COSMF). She also serves on the publications committee of the American Medical Society for Sports Medicine.