ACL, MCL and PCL Injuries

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.

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.

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.

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.

• Our sports medicine and sports surgery team includes experienced pediatric orthopedic surgeons, pediatricians, nurse practitioners, physician assistants, nurses and physical therapists 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.

• 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 growth plates 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 board-certified 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.

• 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 growth plates 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 minimally invasive surgery of the knee for young people.

• 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.

• 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.