Anterior cruciate ligament (ACL) injury

  • What is the ACL?

    The anterior cruciate ligament (ACL) is one of four main ligaments in the knee. Its primary job is to provide stability and reduce stress on the knee joint.

    What is an ACL injury?

    The ACL can be injured in several ways. The most common types of injuries are partial and complete tears of the ACL. Although partial tears can heal on their own, complete tears require surgical reconstruction.

    Another type of ACL injury is a tibial spine fracture, which occurs when the ACL pulls off of the bone. This injury may be treated with a cast or brace if the ACL has not moved. However, if the ACL is displaced, the injury requires surgery to reattach the ACL to the bone.

    In the News

    Suffering on the sidelines, more athletes hit by ACL tears.

    The Boston Globe – South reports on ACL injuries in high school athletes and Boston Children’s Martha Murray, MD, explains that seventy percent of ACL tears are the result of noncontact injuries and the injury is more common among females than males, with the ratio ranging from 2 to 1 to 8 to 1. The Boston Globe – West and The Boston Globe – North also ran stories on the topic. The Boston Globe – West also included tips from Dr. Murray on ACL injury prevention.

    Suffering on the sidelines, more athletes hit by ACL tears.

    Needham High soccer star, other girls coping with rise in ACL tears

    Girls’ soccer players dealing with rise in ACL tears

    Tips to prevent ACL tears.

    ACL injury: Reviewed by Martha Murray, MD
    © Boston Children's Hospital, 2013

    Contact Us

    If your child participates in contact sports, he may be more prone to having ACL injuries. The specialists in the Sports Medicine Program are committed to helping stabilize and re-strengthen your child's ACL, and preventing these types of injuries in the first place through a sports clinic that teaches young athletes how to take proper care of their bodies.

    Boston Children's Hospital
    Sports Medicine Division

    319 Longwood Avenue
    Boston, MA 02115

    Boston Children's Orthopedic Center provides comprehensive assessment, treatment and follow-up care to children who have orthopedic injuries

    Boston Children's Hospital
    Orthopedic Center

    300 Longwood Avenue
    Fegan 2
    Boston, MA 02115


  • How do children sustain ACL injuries?

    The ACL is typically injured during sports participation. Sports that involve frequent cutting and twisting motions, such as football, soccer, basketball, volleyball, skiing and gymnastics, have relatively high rates of ACL injury. Girls are five to eight times more likely than boys to injure their ACLs.

    ACL Injury

    Why have ACL injuries become more common?

    There are several factors behind the increase of diagnosis of ACL injuries, including:

    • Doctors are more aware of the injury, and have become more adept at recognizing it.
    • Newer technologies like MRI and arthroscopy also help doctors better visualize the injury.
    • Children are playing sports at a more competitive level at younger ages, and therefore, are more likely to focus on a single sport.
    • Children are maturing earlier. They are bigger, stronger and faster, which means greater risk for adult-like injuries like ACL tears.

    What factors increase a child’s risk of an ACL injury?

    Teenagers have the highest risk of ACL injuries, since they are the most athletically active demographic group.

    Teenagers who are especially at risk include those who play contact sports (such as football and hockey) and sports that involve cutting and pivoting (such as soccer, basketball, gymnastics, volleyball and baseball).

    Girls are five to eight times more likely than boys to tear their ACLs for several possible reasons:

    • Girls tend to use their ligaments more than their muscles when playing sports.
    • At puberty, boys grow in height and develop their lower leg muscles at the same time. When girls grow, they don’t tend to develop lower leg strength unless they train for it.
    • Girls tend to land in a more straight-legged way than boys, thus reducing the effectiveness of their quads (quadriceps femoris muscles) as shock absorbers.
    • Girls’ knees tend to bend inward during jumping/pivoting/landing moves, which distributes their weight more unevenly than boys.
    • Girls have wider hips (in relation to their knees), which puts more stress on the ACL.
    • Boys tend to use their hamstrings when jumping, while girls tend to use their quads, which put more stress on the ACL.

    Can ACL tears in children be prevented?

    A torn ACL is not strictly a preventable injury, since sports such as basketball, soccer, skiing, gymnastics, volleyball and football put athletes at risk to tear their ACLs. However, ACL injury prevention programs have been shown to reduce athletes’ risk for tearing an ACL. Boston Children’s Hospital’s Orthopedic Center and Sports Medicine Division recommends prevention programs for youth who participate in high-risk sports and post-operative ACL patients, particularly females.

    In general, athletes and active young people can reduce their risk by:

    • maintaining general health and fitness: sport-specific conditioning, diet, exercise, sleep
    • learning/using proper sport-specific movements (form) and techniques
    • wearing/using proper sport-specific gear
    • learning which moves cause risks (risk awareness)
    • hamstring/leg strengthening (especially for girls)

    To learn more about ACL injury prevention, please download Boston Children’s ACL Injury Prevention Guide.

  • How are ACL injuries diagnosed?

    Diagnosis begins with a patient history and physical exam. A child may feel the knee shift or hear a popping sound when the injury occurs. The knee often appears swollen with an ACL tear.

    The doctor (or sometimes a trainer at the scene of the injury) will examine the knee, and in most cases will use a series of flexion/extension maneuvers with the knee to identify which ligaments are injured.

    An MRI is often ordered to confirm the diagnosis. This diagnostic imaging exam can show the severity of the injury and check for damage to other ligaments and tendons.

    An x-ray may be performed to check for any fractures in the bones of the knee. However, since x-rays only produce images of the bone, they can’t detect soft tissues such as ligaments and tendons.

    Is an ACL injury an emergency?

    An ACL is not an emergency, but doctors prefer to see patients as early as possible, so they can begin therapy to reduce swelling and return motion and strength. Orthopedic surgeons prefer to wait a minimum of three weeks from the date of the injury to perform the reconstruction. That’s because the risk of stiffness is higher if surgery is performed too early. However, if surgery is postponed too long, the patient runs the risk of additional injury to other ligaments or cartilage in the knee. Postponing surgery also may lead to progressive damage to the meniscus or knee cartilage.

    What other injuries may occur with an ACL tear?

    About half of children and teens with a torn ACL present with an additional injury to the knee. A common second injury is a torn meniscus; this cartilage acts as a shock absorber in the knee. Patients also may injure the articular cartilage in the knee or other ligaments in the knee. Our orthopedic surgeons recommend very close management of meniscal tears because removing a torn meniscus eliminates an essential shock absorber. Plus, children have greater healing ability than adults.

  • How are ACL injuries treated?

    Research has shown that 75 percent of partial ACL injuries can heal without surgery. Most of these patients are treated with bracing and physical therapy. Most athletes with a partial ACL tear can return to sports three months after the injury.

    Complete tears do not heal on their own. Usually, surgery is indicated.

    Are children candidates for ACL reconstruction surgery?

    Yes, most children make excellent candidates for ACL reconstruction surgery. In the past, most orthopedic surgeons and sports medicine physicians did not recommend surgery for children and teens with torn ACLs. That’s because the conventional surgical approach required the physician to drill through the growth plate (physes), which could disrupt the growth plate. Thus, the standard recommendation was to wait until after puberty to complete the surgery. The problem with this approach is that a child with a torn ACL risks further injury to the knee with even every day activity.

    The orthopedic surgery team at Boston Children’s recognized this dilemma more than 25 years ago, and Lyle Micheli, MD, director of the Sports Medicine Division, and Mininder Kocher, MD, MPH, associate director of the Sport Medicine Division, pioneered physeal-sparing reconstruction surgery and transphyseal reconstruction.


    These physeal-sparing treatment techniques are customized to the growing child’s age: pre-pubescent, adolescent or older adolescent.

    The physeal-sparing surgery eliminates the need to drill tunnels across the growth plate and therefore avoids disturbing the growth plates. Boston Children’s orthopedic surgeons have completed more than 300 physeal reconstruction surgeries on children, with 95 percent of patients returning to sports and no cases of growth plate disturbance. The risk of re-tearing the graft is about 4 percent. This surgery is the preferred approach for pre-pubescent patients up to 13 years old.

    Transphyseal reconstruction 

    Transphyseal reconstruction is closer to a traditional adult surgery, but keeps the primary fixation away from the growth plates. Boston Children’s orthopedic surgeons have completed more than nearly 1,000 transphyseal reconstruction surgeries on pubescent patients, with 95 percent of athletes returning to sports, and no cases of growth plate disturbance. The risk of re-tearing the graft ranges from 5-7 percent. This is the preferred approach for teenagers up to 16 or 17 years old.

    What is the recommended rehabilitation after surgery?

    We recommend most patients start to use an exercise bike right after surgery, enter the water two weeks after surgery, use an elliptical machine at six weeks and begin jogging and running three months after surgery. Most patients return to sports, often with a custom brace, six months after surgery. The brace is usually worn for two years after surgery.

    Are there psycho-social considerations with an ACL injury?

    An ACL tear can have a major psycho-social impact on an athlete and his or her family. Most ACL patients are athletes and their identity and peer group is tied to their athletic persona and teammates.

    We recommend athletes with an ACL injury remain involved with the team and connect with peers who have had an ACL injury. If the patient seems to have a hard time coping, we suggest reaching out to parents, friends or a physician. Our sports psychology team also can help athletes cope with the stress of an injury, as well as fears about re-injury.

    What questions should parents and patients ask their physician?

    • How many ACL reconstruction procedures have you performed on teens and children?
    • What is your success rate?
    • What is your return-to-sports rate?
    • What is your re-tear rate?

    Dr. Mininder Kocher on ACL injury

  • For more than a century, orthopedic surgeons and investigators at Boston Children's have played a vital role in the field of musculoskeletal research—pioneering treatment approaches and major advances in the care and treatment of trauma to the joint, scoliosispolioTBhip dysplasias and traumas to the hand and upper extremities.

    Our advanced research helps answer the most pressing questions in pediatric orthopedics today—providing the children we treat with the most innovative care available.

    ACL research

    Research led by Boston Children’s orthopedic surgeon and principal investigator Martha Murray, MD, focuses on stimulating the healing of tissues inside joints—particularly the ACL and meniscus of the knee.

    Treating these injuries remains one of the most challenging problems facing orthopedic science today, since damaged ACL ligaments have almost no ability to repair or regenerate. Surgery is typically performed to remove the injured tissue and replace it with healthy graft tissue. But this procedure can lead to a high rate of premature arthritis in the knee (as high as 80 percent 14 years after an ACL tear). Physeal-sparing and transphyseal reconstruction surgeries, performed by experts at Boston Children's, are not widely available. The ACL reconstruction technique used on adults isn't suitable for children who are still growing.

    Murray’s Sports Medicine Research Laboratory team is developing a new technique to stimulate natural ACL healing. In animal studies, they’re finding that an enriched collagen gel can stimulate natural healing—creating a “bridge” between the two torn ends that provides a medium for the cells to come back into and heal.

    Fig. 1              Fig. 2              Fig. 3              Fig. 4
    ACL Repair

    1. Fig. 1 ACL is torn
    2. Fig. 2 Healing does not occur when blood clot dissolves in joint fluid
    3. Fig. 3 Collagen and blood plasma mixture is injected
    4. Fig. 4 ACL heals successfully

    Although it will be years before researchers test the technique in patients, it’s already showing promising results in animals, and may help prevent early arthritis by restoring the knee closer to “normal” than grafting. Plus, it’s much less invasive—requiring just two incisions, in contrast to grafting with segments of the patella and/or other tissues. Finally, because the surgical technique is similar to a straightforward fracture repair, most orthopedic surgeons will be able to perform the procedure. Ultimately, this could facilitate broader access to ACL repair for growing children.

    Orthopedic basic science laboratories

    Working in Boston Children’s orthopedic research labs are some of the nation’s leading musculoskeletal researchers. These labs include:

    Ligament and tendon innovations

    Physeal sparing

    A series of innovative, age-specific reconstruction techniques for treating the ACL injuries of growing children has been developed by Boston Children’s orthopedic surgeon and director of the Sports Medicine Division, Lyle Micheli, MD. These are classified as physeal sparing procedures—that is, they spare the child’s growth plates (physes) from disruption that would occur in traditional ACL reconstructive surgery.

    Originally developed as a temporary procedure until a child reached skeletal maturity, follow-up studies have found that up to five years after their surgeries, 95 percent of children who’d had physeal sparing procedures were doing so well that they no longer required ACL reconstructive surgery.

    Platelet-rich plasma

    The Sports Medicine Division is now incorporating the latest in tendon regeneration—the application of platelet-rich plasma. This treatment has been popular in Europe—and now in the United States—for stimulating tissue regeneration in difficult-to-heal areas such as tendons (including the Achilles, elbow and patella) that don’t respond to physical therapy or to limits on activity.

    There are normally many healing growth factors in our platelets. The process involves isolating these growth factors in the patient’s blood platelets and then injecting them into the affected areas with ultrasound guidance.

    The Sports Medicine Division in the Orthopedic Center at Boston Children's conducts research into:

    • the mechanisms of sports injuries
    • the techniques of rehabilitation and treatment
    • the physiology of exercise and conditioning

    Ongoing research includes the study of:

    • knee injuries
    • running injuries
    • injuries to pre-adolescent children
    • the psychological impact of sports and sports injuries
    • the treatment and prevention of injuries to dancers

    Program director Lyle J. Micheli, MD, is one of the world’s leading authorities on sports care. Micheli has treated world-renowned dancers and professional athletes, and is the author of hundreds of published clinical studies, scholarly review articles and books.

  • Boston Children's to the Olympics: Overcoming an ACL injury


    ACL surgery 10 years later: an athlete looks back

    The decision to proceed with anterior cruciate ligament (ACL) reconstruction to treat a torn ACL on a growing child can be difficult. Parents often weigh the pros and cons of surgery versus the risks of a more conservative approach with limited activity. After surgery, they wonder how to best help their child manage the difficult recovery period and return to sports. As with many parenting challenges, there is no single right answer. Nearly 10 years after his ACL surgery, University of Michigan sophomore Gabe Kahn reflects on his story.

    Beating the odds: After three knee injuries, a female athlete triumphs

    There is a special kind of female athlete who is so dedicated that her sport becomes her life. Because research shows that girls and women are prone to higher rates of injuries and other health complications, these female athletes require a level of dedication not only to their sports, but also to their long-term health. And by pairing the two, they prevail.

    ACL injury - Stephanie's story

    Once an adult injury, ACL tears are on the rise in kids

    Increase linked to better diagnostics and dramatic growth in competitive sports

    Eleven-year-old Josie Berg-Hammond was running sideways in gym class when her right knee popped and buckled. She had torn a ligament, but surgery was delayed for two years because she was still growing.

    As the preteen waited for the operation on her anterior cruciate ligament, or ACL, she was encouraged to remain active. But her unstable knee kept giving out. Now, more than a decade after surgery, Berg-Hammond says she has constant pain in her knee.

    "It hurts to walk and to do any sort of physical activity," said Berg-Hammond, 24, of Chicago, who never dreamed her childhood mishap might have lifelong consequences.

    One patient's story: From torn ACL to MVP

    For kids like 8-year-old Fletcher Gallimore, playing sports is part of their identity. But in September of 2011, Fletcher—who loves football and basketball—was accidentally pushed into a post during football practice, hitting his knee. And the accident took him and his parents down a path they never imagined.

    Boston Children's in the news: ACL on the rise in young athletes

    BC World News recently ran a story featuring Boston Children's Hospital patient Caleb Seymour, an 8-year-old football player who tore his anterior cruciate ligament (ACL) on the field. Unfortunately, Caleb is just one of many young athletes facing this type of knee injury. Recent data shows ACL tears are rising rapidly among young people, and their long-term effects can be substantial. Kids who suffer serious ACL damage can have life-long problems with leg mobility, uneven leg growth or arthritis.

    Girls' soccer ACL injuries are preventable

    More girls are playing soccer than ever and as you can guess, that means more girls are suffering from soccer-related injuries. A study published in the Archives of Internal Medicine takes a look at a Swedish research exercise program designed to help girls prevent one of soccer’s most common injuries – a torn anterior cruciate ligament (ACL).


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Overcoming an ACL injury - Olympic bound slopestyle skier Julia Marino

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The future of pediatrics will be forged by thinking differently, breaking paradigms and joining together in a shared vision of tackling the toughest challenges before us.”
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