ACL, MCL and PCL Injuries

What are ACL, MCL and PCL injuries?

ACL, MCL and PCL injuries are damage to ligaments that keep the knee from wobbling or giving out when you move. These ligaments are the anterior cruciate ligament (ACL), medial collateral ligament (MCL) and posterior cruciate ligament (PCL). When the knee is forced into an unusual position, 1 or more of the ligaments can tear, either part way or all the way.

  • How does the knee work?

    To understand knee ligament injuries, 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 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 of the shinbone to the back of the thighbone so the shin does not slide in front of the thigh.
    • The PCL connects the back of the shinbone to the front of the thighbone so the shin does not slide behind the thigh.

    Two ligaments run along either side of the knee.

    • The 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.
  • What causes an ACL injury, and who is at risk?

    ACL tears can happen when someone:

    • Stops or changes direction suddenly.
    • Twists their knees.
    • Bends their knees sideways.

    This can happen during accidents while skiing, bicycling or riding in a car. It also can happen during sports that involve a lot of jumping, pivoting and quick stops and starts, such as basketball, volleyball and soccer. Children, teens and young adults sometimes 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 young athletes. Researchers think this may be due to 3 main reasons: 

    1. More children and teens are involved in sports.
    2. Doctors are more likely to recognize knee injuries in children and teens.
    3. We are getting better at diagnosing 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. It may have to do with anatomy, muscle strength, coordination and hormonal differences.

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

  • What causes an MCL injury, and who is at risk?

    When the knee suddenly bends inward with the foot bent outward, the MCL can tear. These kinds of injuries can happen when athletes collide in football, soccer and ice hockey and during car accidents.

    MCL injuries sometimes happen along with ACL tears.

    MCL tears, while common in adults, are less common for children. But teen athletes are more likely to injure their MCL than other teenagers. This is most true if they play sports in which they might collide with other players from the side.

    Older children, teens and young adults are more likely to injure their MCL than children younger than 12. Younger children more often break the bone where the ligament attaches.

  • What causes a PCL injury, and who is at risk?

    In young people, PCL injuries most often happen during high-speed sports, such as basketball and soccer.

    A blow to the front of the knee — for example, from hitting the dashboard during a car accident or falling hard on a bent knee during a football game — can also injure the PCL.

    Teen athletes who play high-speed sports are more likely to injure their PCL than other young people. In teens especially, accidents also cause PCL injuries.

    Teens and young adults are more likely to injure their PCL than children under 12. Younger children more often break the bone where the PCL attaches.

Why choose Seattle Children’s for treatment of ACL, MCL and PCL injuries?

Seattle Children’s Orthopedics and Sports Medicine specialists treat ACL, MCL and PCL injuries in children, teens and young adults up to age 21.


  • The knee experts you need are here
    • Our sports medicine and sports surgery team includes experienced pediatric , , , , nurses and who know how to evaluate and treat all types of knee problems.
    • Young people with ACL tears and some with MCL or PCL tears need surgery. For those who do, we have pediatric orthopedic surgeons with expanded fellowship training in sports medicine.
    • To restore health and function, we also use nonsurgical methods, like physical therapy (PT), including sports PT. We have the largest team of physical therapists in the Pacific Northwest who specialize in the care of babies, children, teens and young adults.
  • Knee care from birth through young adulthood
    • Our experts have the knowledge, training and skills to treat the youngest children, who are still growing, through young adults in their early 20s. We have special training in the physical, emotional and social needs of young people of all ages.
    • We tailor treatment to each person’s specific problem and consider their age and development. Young people with knee injuries may need different care than adults do. When treating a torn ligament in a growing child, doctors must take into account the  on bones above and below the knee.
    • For imaging that uses radiation, we use the lowest amount possible (PDF) to make the best image. We have a low-dose radiation X-ray machine, called the EOS. It makes safer full-body images. We also have the largest group of pediatric radiologists in the Northwest.
    • Athletic trainers from our Sports Medicine Program work at dozens of area schools. They teach conditioning, assess and treat injuries and refer athletes to medical providers, all with an eye to keeping your child or teen active for years to come.
  • Our approach to surgery improves life for our patients
    • We offer multiple options for replacing a young person’s torn ligament with other tissue. We are careful to select the option that best matches each patient’s condition.
    • We recommend surgery only when we believe it will provide the best outcomes. First, we look at each patient as a whole person. The team will take many factors into account. These include how serious the knee injury is, its health effects, if the body is still growing and what results you can expect from treatment.
    • Our surgical methods limit the risks of injury to in children who are still growing. This increases the chances that your child will be able to return to sports.
    • Seattle Children’s surgeons are experienced in of the knee for young people.
  • Support for the best recovery
    • Your team at Seattle Children’s does more than plan and provide care. We also make sure you and your family understand the injury and treatment options. We support you in making choices that are right for your family.
    • Our rehabilitation programs are designed so that each patient will get back range of motion, rebuild strength and stability, restore balance and regain confidence in using their knee.
    • To help patients return to play 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 at our hospital campus and Odessa Brown Children’s Clinic Othello in Seattle as well as in Bellevue, Everett and Federal Way to make ongoing rehab easier for you.
    • Seattle Children’s supports your family with a range of resources. Our Child Life specialists, Family Resource Center and Guest Services are here to help.
  • Research to improve care
    • Our team members partner with experts at other children’s hospitals on multicenter studies. Together, they work to understand more about the best ways to treat knee injuries in young people.
    • We track results of our patients so we can improve care and provide families with accurate information about our success rates, the risk of complications and the chance that patients will return to their previous level of activity. To help with this effort, we may ask you or your child to fill out questionnaires about their knee function after treatment.
    • Carefully choosing when to return to sports is key to long-term success after an injury. We have done a great deal of research on how to use return-to-sport testing to guide patients recovering from a torn knee ligament.
    • Orthopedics and sports medicine care is about more than just the joints, muscles and bones. For example, we know that physical health and mental health can affect each other. We have done research on topics like depression symptoms in those with an ACL injury so we can better address all of our patients’ needs.
    • Learn more about current orthopedics research at Seattle Children’s.

What are the symptoms of ACL, MCL and PCL injuries?

If the knee of a child, teen or young adult suddenly swells after an accident or injury, they may have a torn ACL, MCL or PCL or another serious knee problem. Other symptoms of knee ligament injuries include:

  • A popping sound at the time of the injury
  • Pain in the knee
  • Knee is wobbly or unstable

How are ACL, MCL and PCL injuries diagnosed?

To help prevent further injuries to the bones and joints, it is important to get a thorough evaluation and proper treatment.

At our clinic, the doctor will:

  • Ask what happened before the knee began to swell and hurt.
  • Examine the knee. To doctors trained in sports medicine, knees with ACL, MCL or PCL tears often feel loose.

We cannot be sure that a knee ligament is torn until the swelling in the knee has gone down. This usually takes 7 to 10 days. At that time, we may take:

  • of the knee to get more information on what is wrong
  • An  if it is not clear that a ligament is torn or if we think there may be other injuries

How are ACL, MCL and PCL injuries treated?

Young people with a torn ACL need surgery to repair or reconstruct the ligament and then physical therapy (PT) to help them get back to their usual activities. If they are still growing, it’s important to receive care from a pediatric orthopedic surgeon who knows how to protect their .

For MCL and PCL injuries, we use nonsurgical methods like PT, including sports PT, whenever possible. Those who have an MCL injury may need to wear a hinged knee brace along with doing PT.

Surgery for ACL, MCL and PCL injuries

Illustration of a new ACL placed in the knee and attached to the lower thigh bone and upper shinboneSurgery to repair a torn ACL, called transepiphyseal anterior cruciate ligament reconstruction. The red lines are the new ligament. The black dots show where the surgeon secures the new ligament to the thighbone above the knee and the shinbone below the knee.

Seattle Children’s pediatric orthopedic surgeons have the training and experience to repair knee ligaments for children, teens and young adults.

Surgery is the usual treatment after an ACL injury to make the knee stable again.

During ACL surgery, the surgeon replaces the torn ligament with new tissue that will turn into ligament over time. This tissue (called a graft) is taken from another body site and transferred to the new area. Graft tissue can be taken from the patient’s own body or from a donor (cadaver). The surgeon will talk with you in advance about the pros and cons of different types of grafts.

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 surgeon inserts a small tool called an arthroscope into the 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).

A young person who has both an MCL injury and an ACL injury probably will need surgery to reconstruct the ACL.

Surgery is not usually used to treat PCL injuries that happen by themselves. But surgery may be needed if:

  • A PCL injury happens along with an injury to the ACL or another part of the knee.
  • An injury moves the piece of bone the PCL is attached to far from its usual place on the shinbone. Surgeons can put the bone back and attach it again.

Physical therapy for ACL, MCL and PCL injuries

PT is an important part of getting better after surgery for any knee ligament injury. It will help strengthen the muscles around the knee and make the joint stable.

If an MCL or PCL injury is mild, a child, teen or young adult may be able to recover with PT alone. Our staff is expert at devising and teaching exercise programs to help patients:

  • Recover range of motion
  • Rebuild strength and stability
  • Restore balance
  • Regain confidence in using their knee

Seattle Children’s has PT facilities for sports medicine dedicated to helping with recovery. Most patients will have PT sessions with us a couple of times a week until they meet their goals for returning to their sport or other usual activities. Afterward, our therapists may also recommend exercises to keep doing at home. 

To prevent new or repeat injuries, we have a strong focus on return-to-sport testing. Our PTs know how to check when a patient is ready to be more active or go back to their sport. We have done a great deal of research to understand how to make these decisions so each patient gets the best possible results.

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

Contact Us

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

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