ACL Injuries

What is an ACL injury?

ACL injuries are damage to the anterior cruciate ligament (ACL) in the knee. The ACL is one of four ligaments that keep the knee from wobbling or giving out when you move.

  • To understand ACL injury, it helps to know a little about how the knee works.

    The knee is a large joint where the shinbone (tibia) meets the thighbone (femur). Two ligaments run along either side of the knee.

    • The medial collateral ligament (MCL) is on the inside and keeps the knee from bending in.
    • The lateral collateral ligament (LCL) is on the outside and keeps the knee from bending out.

    Two other ligaments – the ACL and the posterior cruciate ligament (PCL) – cross each other in the middle of the knee. They work together to keep the shinbone attached to the thighbone. 

    The ACL connects the front part of the shinbone to the back part of the thighbone so that the shinbone does not slide in front of the thighbone.

  • When the knee is forced into an unusual position, the ACL and other ligaments can tear, either partially or all the way. ACL tears occur when children:

    • Stop or change direction suddenly.
    • Twist their knees.
    • Bend their knees sideways.

    This can happen during accidents while skiing, bicycling or riding in a car. It also can happen during sports that require a lot of jumping, pivoting and quick stops and starts, such as basketball, volleyball and soccer. Children sometimes also tear their ACL when they stumble or fall, or when they run into others while playing sports.

  • Injuries to the ACL are becoming more common in growing athletes. Researchers think this may be due to 3 main reasons: 

    1. More children are involved in sports.
    2. Doctors are more likely to recognize knee injuries in children.
    3. We are getting better at identifying injuries to the ligaments.

    Teenage girls are 2 to 8 times more likely to injure their ACL than are boys of the same age. We do not know exactly why this is so, but it may have to do with anatomy, muscle strength, coordination and hormonal differences.

    Older children have more ACL injuries than younger children. Until about age 12, children are more likely to break the bone where the ligament attaches.

ACL Injuries at Seattle Children’s

Seattle Children’s treats the full range of bone, muscle and joint conditions, including ACL, MCL and PCL injuries.

    • Your child is cared for by an orthopedics team, including pediatricians, pediatric orthopedic surgeons, nurse practitioners, physician assistants, nurses and physical therapists.
    • To restore your child’s health and function, we use nonsurgical methods, like physical therapy (PT), including sports PT, whenever possible. We have the largest team of physical therapists in the Pacific Northwest who specialize in the care of babies, children, teens and young adults.
    • If your child does need surgery, we have pediatric orthopedic surgeons with expanded fellowship training in sports medicine and the experience to repair knee ligaments.
    • A child’s knee injury is more difficult to treat than an adult’s. This is because doctors must avoid injury to the growth plates on children’s bones above and below the knee. Here, your child’s team has special training in the medical and surgical needs of young people.
    • We have the largest group of board-certified pediatric radiologists in the Northwest. If your child needs imaging that uses radiation, we use the lowest amount possible (PDF) to produce the best image.
    • Athletic trainers from our Sports Medicine Program work at dozens of area schools, teaching conditioning, assessing and treating injuries and referring athletes to medical providers, all with an eye to keeping your child active for years to come.
    • We perform surgery to reconstruct torn ACLs in young athletes whose knees either do not respond to physical therapy or are too wobbly to allow them to return to sports.
    • Our surgical methods limit the risks of injury to growth plates. This increases the chances that your child will be able to return to sports.
    • Our rehabilitation programs are designed so that your child will recover range of motion, rebuild strength and stability, restore balance and regain confidence in using their knee.
    • To help your child return to play quickly and safely, we do more than treat their current injury. We focus on preventing repeat or new injuries.
    • For your convenience, our doctors see patients at several locations around Washington. Seattle Children’s sports physical therapy is available in Seattle, Bellevue, Everett and Federal Way to make ongoing rehab easier for you.

Symptoms of PCL Injuries

If your child’s knee suddenly swells after an accident or injury, they may have a torn ACL or another serious knee problem. Besides swelling, symptoms of ACL injuries include:

  • A popping sound at the time of the injury
  • Severe pain
  • Later, knee feels unstable

Diagnosing ACL Injuries

To help protect your child from more injuries that could hurt growing bones and joints, it is important to get a thorough evaluation and proper treatment.

  • When you and your child come to our clinic, we:

    • Ask what happened before the knee began to swell and hurt.
    • Examine your child’s knee. To doctors trained in sports medicine, knees with ACL tears often feel loose.
  • We cannot be sure that your child has a torn ACL until the swelling in the knee has gone down. This usually takes 7 to 10 days. At that time, we may take:

    • Radiographs of your child’s knee to get more information on what is wrong
    • An MRI (magnetic resonance imaging) scan if it is not clear that the ACL is torn or if we think your child may have other injuries

Treating ACL Injuries

It’s desirable to treat an ACL injury with methods that do not require surgery. This is especially true with growing children and teenagers.

Seattle Children’s has physical therapy facilities for sports medicine dedicated to helping your child recover from injury. If your child does need surgery, we have pediatric orthopedic surgeons with the training and experience to repair knee ligaments for children and teens.

  • If your child’s injury is mild, they may be able to recover with the help of physical therapy alone. Our staff is expert at devising and teaching exercises that help bring back motion in your child’s knee and strengthen the muscles around it.

    We have a dedicated sports gym to help our patients with rehabilitation.

    One of the most important ways to prevent repeat injuries is to modify activities that might hurt the knee as it heals. These activities include high-level athletics that require:

    • Jumping
    • Pivoting
    • Contact with other players
    • Playing on an uneven surface
  • This repair uses a hamstring tendon graft (red). The repair is mostly anatomic but extends through the physes (green arrows). Courtesy of 'Fundamentals of Pediatric Orthopedics,' ©2003 Lippincott Williams & Wilkins

    Transepiphyseal anterior cruciate ligament reconstruction.

    Your child may need surgery if:

    • The injury is severe.
    • Physical therapy does not make the knee stable enough to return to sports.

    The goal of surgery in young patients is to make their knees stable with the least possible risk of affecting their growth.

    During surgery, orthopedic surgeons use tissue taken from your child’s hamstring tendons to reconstruct the ACL. We drill small holes in the shinbone and the thighbone. Then, we pass the new ligament through the drill holes and secure it to the bones.

    This surgery requires only small incisions. The surgeons insert a tool called an arthroscope into your child’s knee. They use pictures displayed on a large monitor to guide their actions. Learn more about arthroscopic surgery (PDF) and graft choices for ACL surgery in youth (PDF).

    After surgery, your child will have regular physical therapy, most likely twice a week for 4 to 8 weeks. This will help strengthen muscles and stabilize the knee. Your child probably will need physical therapy for 9 months to a year after surgery.

    Read more about arthroscopic and minimally invasive surgery for ACL reconstruction.

Contact Us

Contact Orthopedics and Sports Medicine at 206-987-2109 for an appointment, a second opinion or more information.

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