CLINICAL REPORT

Anterior Cruciate Ligament Injuries: Diagnosis,Treatment, and Prevention

abstractThe number of anterior cruciate ligament (ACL) injuries reported inathletes younger than 18 years has increased over the past 2 decades.Reasons for the increasing ACL injury rate include the growing numberof children and adolescents participating in organized sports, inten-sive sports training at an earlier age, and greater rate of diagnosisbecause of increased awareness and greater use of advanced medicalimaging. ACL injury rates are low in young children and increasesharply during puberty, especially for girls, who have higher ratesof noncontact ACL injuries than boys do in similar sports. Intrinsic riskfactors for ACL injury include higher BMI, subtalar joint overpronation,generalized ligamentous laxity, and decreased neuromuscular controlof knee motion. ACL injuries often require surgery and/or many monthsof rehabilitation and substantial time lost from school and sports par-ticipation. Unfortunately, regardless of treatment, athletes with ACLinjuries are up to 10 times more likely to develop degenerative arthritisof the knee. Safe and effective surgical techniques for children and ado-lescents continue to evolve. Neuromuscular training can reduce risk ofACL injury in adolescent girls. This report outlines the current state ofknowledge on epidemiology, diagnosis, treatment, and prevention of ACLinjuries in children and adolescents. Pediatrics 2014;133:e1437–e1450

INTRODUCTION

Anterior cruciate ligament (ACL) injuries are a serious concern forphysically active children and adolescents. The ACL is 1 of the 4 majorligaments that stabilize the knee joint (Fig 1). Its main function is toprevent the tibia from sliding forward relative to the femur. The ACLalso assists with preventing excessive knee extension, knee varus andvalgus movements, and tibial rotation.1,2 An intact ACL protects themenisci from shearing forces that occur during athletic maneuvers,such as landing from a jump, pivoting, or decelerating from a run.

Physicians caring for young athletes have noted an increase in thenumbers of ACL injuries over the past 2 decades.3,4 Reasons for theincrease in ACL injury rate include the growing number of childrenand adolescents participating in organized sports, increased partic-ipation in high-demand sports at an earlier age, and a greater rate ofdiagnosis as a result of increased awareness that ACL injuries canoccur in skeletally immature patients and more frequent use of ad-vanced medical imaging.4–8

Cynthia R. LaBella, MD, FAAP, William Hennrikus, MD, FAAP,Timothy E. Hewett, PhD, FACSM, COUNCIL ON SPORTSMEDICINE AND FITNESS, and SECTION ON ORTHOPAEDICS

KEY WORDSknee injuries, athletes, sports, adolescents

ABBREVIATIONSACL—anterior cruciate ligamentCI—confidence interval

This document is copyrighted and is property of the AmericanAcademy of Pediatrics and its Board of Directors. All authorshave filed conflict of interest statements with the AmericanAcademy of Pediatrics. Any conflicts have been resolved througha process approved by the Board of Directors. The AmericanAcademy of Pediatrics has neither solicited nor accepted anycommercial involvement in the development of the content ofthis publication.

The guidance in this report does not indicate an exclusivecourse of treatment or serve as a standard of medical care.Variations, taking into account individual circumstances, may beappropriate.

All policy statements from the American Academy of Pediatricsautomatically expire 5 years after publication unless reaffirmed,revised, or retired at or before that time.

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EPIDEMIOLOGY OF ACL INJURY

The incidence of ACL injuries in thegeneral population can be estimatedfrom national registries, which wereestablished in Norway (2004), Denmark(2005), and Sweden (2006) to monitorthe outcomes of ACL reconstructionsurgery. Between 2006 and 2009, allNorwegian hospitals participated in theregistry, with a total compliance of 97%.In the 10- to 19-year age group, theannual incidence of primary ACLreconstructions was 76 per 100 000girls and 47 per 100 000 boys.9 Thisnumber underestimates the true in-cidence of ACL injuries, however, be-cause it does not include those treatednonoperatively.

Most ACL injuries are sports-related;therefore, injury rates are higher inathletes. The National Collegiate AthleticAssociation Injury Surveillance Systemhas compiled data for 16 sports (8men’s and 8 women’s) over 16 yearsfrom a sample of colleges and univer-sities (approximately 15%).2 ACL injuryrates were highest in men’s springfootball and women’s gymnastics (33

per 100 000 athlete-exposures) (Fig 2).In women’s sports, ACL injury ratesrepresented a larger proportion oftotal injuries than in men’s sports(3.1% vs 1.9%), with women’s basket-ball and women’s gymnastics toppingthe list at 4.9% of total injuries.10

Overall, high school athletes have lowerrates of ACL injuries than do collegiateathletes (5.5 vs 15 per 100 000 athlete-exposures) but a similar injury distri-bution across sports.2,11 Since 2005,the National High School Sports-Related Injury Surveillance Study hascompiled data on the incidence of ACLinjuries in 18 sports.11 From 2007 to2012, ACL injury rates were highest ingirls’ soccer and boys’ football (11.7and 11.4 per 100 000 athlete-exposures,respectively) (Fig 3).

No well-designed epidemiologic studiesto document ACL injury rates have beenconducted in children younger than 14years. Although there have been reportsof sport-related ACL injuries in childrenas young as 5 years, the limited dataavailable suggest that ACL disruptions inchildren younger than 12 years arerare.12–16 McCarroll et al16 found that ofthe 1722 ACL injuries diagnosed over

a 6-year period at their sports medicinecenter, 57 (3%) were in children 14years and younger. The Norwegian ACLSurgical Registry collects data for allACL surgeries performed at participat-ing institutions nationwide. From 2004to 2011, this registry recorded a total ofonly 8 to 9 ACL surgeries each year forchildren 11 to 13 years of age. Thisrepresents a small fraction (0.6%) of thetotal number of ACL surgeries recordedeach year (1441) in this registry acrossall age groups. For the children whohad surgery, the age at the time of in-jury ranged from 9 to 13 years.

The ACL surgery rate for 12- to 13-year-olds (3.5 per 100 000 citizens) wassubstantially lower than that for 16- to39-year-olds (85 surgeries per 100 000citizens), the age group at highest risk.9

Again, these numbers underestimatethe actual injury rates, because they donot account for those treated non-operatively.

Gender Differences

ACL injury risk begins to increase sig-nificantly at 12 to 13 years of age in girlsand at 14 to 15 years of age in boys.9,12

Female athletes between 15 and 20

FIGURE 1Anatomic structures of the knee. LCL, lateralcollateral ligament; MCL, medial collateral ligament;PCL, posterior cruciate ligament. (Reproducedwith permission from Harris SS, Anderson SJ,eds. Care of the Young Athlete. 2nd ed. Elk GroveVillage, IL: American Academy of Pediatrics andAmerican Academy of Orthopedic Surgeons;2009:410.)

FIGURE 2Collegiate ACL injury rates per 1000 athlete-exposures by sport. (Reproduced with permission fromRenstrom P, Ljungqvist A, Aremdt E, et al. Non-contact ACL injuries in female athletes: an internationalOlympic committee current concepts statement. Br J Sports Med. 2008;42(6):395.10)

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years of age account for the largestnumbers of ACL injuries reported(Fig 4). The gender disparity in ACL in-jury rates among athletes begins toappear around the time of the growthspurt (12–14 years of age for girls and14–16 years of age for boys), peaksduring adolescence, then declines inearly adulthood.10,12 At the high schoollevel, ACL injury rates in gender-comparable sports (soccer, basketball,baseball/softball, track, volleyball) are

2.5 to 6.2 times higher in girls comparedwith boys.10,11,17 In college athletics,ACL injury rates are 2.4 to 4.1 timeshigher for women, and at the pro-fessional level, ACL injury rates for menand women are essentially equal.4,10,18

In high school sports, ACL injuriesrepresent a higher proportion of allinjuries in female versus male athletes(4.6% vs 2.5%), with girls’ basketballtopping the list (6%), followed by girls’soccer, girls’ gymnastics, and girls’

volleyball (each 5%). Compared withboys, girls are more likely to havesurgery and less likely to return tosports after an ACL injury.17,19 Amongfemale high school basketball players,knee injuries were the most commoncause of permanent disability, ac-counting for up to 91% of season-ending injuries and 94% of injuriesrequiring surgery.20,21

CONSEQUENCES OF ACL INJURY

An ACL injury at an early age is a life-changing event. In addition to surgeryand many months of rehabilitation, thetreatment costs can be substantial($17 000–$25 000 per injury), and thetime lost from school and sports par-ticipation can have considerable effectson the athlete’s mental health and ac-ademic performance.22,23 Although ACLinjuries account for approximately 3%of all injuries in college sports, theyaccount for 88% of injuries associatedwith 10 or more days of time lost fromsports participation. Freedman et al24

examined the academic transcripts ofcollege students who underwent ACLreconstruction surgery. Compared withan age-matched control group, thosewho had surgery had a significant dropin grade point average of 0.3 pointsduring the semester of injury (P = .04).Similarly, Trentacosta et al25 found thatathletes 18 years and younger who hadACL reconstruction surgery during theschool year reported that it had a neg-ative effect on their grades.

Beyond these more immediate effects,an ACL injury also has long-term healthconsequences. Regardless of the typeof treatment, athletes with ACL injuryare up to 10 times more likely to de-velop early-onset degenerative kneeosteoarthritis, a condition that not onlylimits one’s ability to participate insports but also often leads to chronicpain and disability.26,27 A systematicreview of a series of long-term studiessuggests the rates of degenerative

FIGURE 3High School ACL injury rates per 100 000 athlete exposures (AEs) by sport. (Data from the NationalHigh School Sports-Related Injury Surveillance Study, 2007–08 to 2011–12 school years. Reproducedwith permission from Comstock R, Collins C, McIlvain N. National High-School Sports-Related InjurySurveillance Study, 2009–2010 School Year Summary. Columbus, OH: The Research Institute at Na-tionwide Children’s Hospital; 2010. Available at: http://www.nationwidechildrens.org/cirp-rio-study-reports.11)

FIGURE 4Distribution of patients in the Norwegian National Knee Ligament Registry by age and gender.a

(Reproduced with permission from Renstrom P, Ljungqvist A, Aremdt E, et al. Non-contact ACLinjuries in female athletes: an international Olympic committee current concepts statement. Br JSports Med. 2008;42(6):395.10) aNumber of cases (y-axis) indicates number of ACL reconstructions.

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knee osteoarthritis 10 to 20 years af-ter ACL injury are more than 50%.27

This means children and teenagerswho suffer ACL injuries are likely toface chronic pain and functional limi-tations from knee osteoarthritis intheir 20s and 30s. None of thesestudies, however, demonstrated thatACL reconstruction lowered the riskfor osteoarthritis. In fact, one 5-yearprospective study showed that patientswho had ACL reconstruction had ahigher level of knee arthrosis on radio-graphs and bone scans, compared withpatients who did not undergo ACL re-construction.28

INJURY MECHANISMS

The mechanism of ACL injuries inathletes is likely multifactorial. Pro-posed theories to explain the mecha-nisms underlying ACL injury includeextrinsic (physical and visual pertur-bations, bracing, and shoe-surfaceinteraction) and intrinsic (anatomic,hormonal, neuromuscular, and bio-mechanical) variables. Identification ofextrinsic and intrinsic risk factorsassociated with the ACL injury mech-anism provides direction for targetedinterventions to high-risk individuals.

At least 70% of ACL injuries are non-contact in nature29,30; however, thespecific definition of a noncontact ACLinjury varies from study to study. Somedefine a noncontact ACL injury as onethat occurs in the absence of a player-to-player (body-to-body) contact. Othersdefine noncontact ACL injury as onethat occurs in the absence of a directblow to the knee. An ACL injury result-ing from body-to-body contact but withno direct blow to the knee may beclassified as “noncontact ACL injurywith perturbation.”

Video analysis of ACL injury duringcompetitive sports play indicatesa common body position associatedwith noncontact ACL injury (Fig 5) inwhich (1) the hip is internally rotated,

(2) the knee is close to full extension,(3) the foot is planted, and (4) thebody is decelerating, leading to ap-parent valgus collapse of the knee or“dynamic knee valgus.”31–33 ACL injuryis also observed to occur when thebody’s center of mass is behind andaway from the base of support or thearea of foot-to-ground contact.31

RISK FACTORS

ACL injury risk in young athletes islikely multifactorial. Injury data frommany fields demonstrate that numerousphysical and psychological parametersaffect ACL injury rates.

Genetics

Genetic factors likely play a role, al-though the genetic underpinnings ofincreased ACL injury risk have onlyrecently begun to be examined.34

Hormones

Hormonal factors also likely play a role;however, results of studies investigat-ing hormonal factors are both equivo-cal and controversial.35 Although thefemale knee appears to get slightlymore lax, on the order of 0.5 mm, atmidmenstrual cycle, injuries tend tocluster near the start of menses at thepolar opposite time in the cycle.36,37

Previous Injury

Similar to other musculoskeletalinjuries, one of the single best pre-dictors of future ACL injury is previousACL injury. One study found the in-cidence rate of ACL injury in athleteswho have had ACL reconstruction was15 times greater than that of controlsubjects.38 Female athletes were 4times more likely to suffer a secondACL injury in either knee and 6 times

FIGURE 5Dynamic knee valgus: hips are internally rotated and adducted, tibiae are externally rotated, and feetare everted.

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more likely to suffer a new ACL injuryin the contralateral knee than maleathletes. In fact, subsequent injuriesto the contralateral ACL are twice ascommon as reinjury of the recon-structed ACL (11.8% vs 5.8%).39 Ge-netic, anatomic, and neuromuscularfactors likely play a role.

Age and Gender

Although ACL injury rates increase withage in both genders, girls have higherrates immediately after the growthspurt.9–12,16 It is likely that the increa-ses in body weight, height, and bonelength during pubertal developmentunderlie the mechanism of increasedrisk of ACL injury with increasing age.During puberty, the tibia and femurgrow at a rapid rate.40 This growth ofthe 2 longest levers in the human bodytranslates into greater torques on theknee.41 Increasing height leads toa higher center of mass, making mus-cular control of this center of massmore challenging. Increasing bodyweight is associated with greater jointforce that is more difficult to balanceand dampen during high-velocity ath-letic movements. In pubertal boys, tes-tosterone mediates significant increasesin muscular power, strength, and co-ordination, which affords them withgreater neuromuscular control of theselarger body dimensions. Pubertal girlsdo not experience this same growthspurt in muscular power, strength, andcoordination, which likely explains theirhigher rates of ACL injuries comparedwith pubertal boys.41 That preado-lescent athletes show no gender dif-ferences in ACL injury rates furthersupports this theory.12

Anatomic/Anthropometric Factors

Greater weight and BMI have beenassociated with increased risk of ACLinjury.31,42 A study of military recruitsfound that body weight or BMI >1 SDabove the mean was associated with

a 3.2 and 3.5 times greater risk of ACLinjury, respectively.42 In a study of fe-male soccer players older than 8years, BMI was a significant risk fac-tor for knee injury.31

An increased quadriceps angle (Q an-gle) has been postulated as a riskfactor, but there have been no pro-spective clinical studies to investigatethe relationship between Q angle andACL injury risk.43–45 A narrow inter-condylar notch, where the ACL ishoused, is proposed to increase ACLinjury risk, because a narrow notchtends to be associated with a smaller,weaker ACL and also could cause in-creased elongation of the ACL underhigh tension.46,47 Some studies haveshown that a narrow notch increasesrisk of ACL injury42,47,48; however, oth-ers have shown no association be-tween notch width and ACL injury.18,49,50

Subtalar joint overpronation has beenassociated with noncontact ACL inju-ries,51 likely because overpronationincreases anterior translation of thetibia with respect to the femur, therebyincreasing the strain on the ACL.52

Generalized joint laxity and knee hy-perextension were found to signifi-cantly increase the risk for ACL injuryin female soccer players.53 Patientswith ACL injury have significantlymore knee recurvatum at 10 and 90degrees of hip flexion and an in-creased ability to touch palms tofloor.29 Athletes with generalized jointlaxity had a 2.7 times greater risk ofACL injury than did those withoutgeneralized laxity, and those with in-creased anterior-posterior laxity ofthe knee, as measured by a kneearthrometer, had an approximately 3times greater risk of ACL injury thandid those without such laxity.42 Jointlaxity affects not only sagittal kneemotion (hyperextension) but alsocoronal knee motion (valgus), whichcan strain the ACL and be related toincreased risk in athletes.29,42,54

Neuromuscular Factors

Muscle strength and coordination havea direct effect on themechanical loadingof the ACL during sport movements.55,56

Poor neuromuscular control of the hipand knee and postural stability deficitshave been shown to be risk factors forACL injury.54,57 Landing and pivotingsports involve a great deal of rapiddeceleration and acceleration move-ments that push and pull the tibia an-teriorly and place the ACL under stress.This tibial translation can be modulatedby hamstrings and quadriceps activ-ity.58,59 In vivo studies show when sub-jects were asked to contract theirmuscles, knee laxity is reduced by 50%to 75%.58 Activation of the quadricepsbefore the hamstrings, a pattern morefrequently seen in female individuals,increases the anterior shear force thatdirectly loads the ACL and also could berelated to increased dynamic valgusalignment at initial contact during cut-ting and landing maneuvers.41,60–65 Al-though fatigue is often cited as apotential risk factor for ACL injury, thereare relatively few published studies tosupport or refute this.66

MAKING THE DIAGNOSIS

History

The patient with an acute ACL teartypically presents with pain, a knee ef-fusion, a reduction in knee motion, anddifficulty bearing weight. Often a “pop” isheard or felt by the athlete at the timeof injury. The prevalence of an ACL tearin a pediatric athlete with a traumaticknee hemarthrosis is about 65%.67 Thepatient with a chronic ACL tear typicallypresents with recurrent effusions andthe sense that the knee “gives way” oris unstable with attempts at cutting,twisting, or jumping sports.

Physical Examination

In a pediatric athlete with an acutetraumatic knee effusion, the Lachmantest, anterior drawer test, and pivot

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shift test are clinical examinations thataid in making the diagnosis of an ACLtear.

The Lachman test is performed withthe patient supine (Fig 6). The injuredknee is flexed to 30 degrees. The ex-aminer places 1 hand behind the tibiawith the examiner’s thumb on thetibial tubercle and the other hand onthe patient’s lower thigh. The tibia ispulled anteriorly. Examinations of bothknees are compared. Increased ante-rior movement of the tibia relative tothe femur without a firm end pointcompared with the examination of theuninjured knee suggests a torn ACL.

The anterior drawer test also is per-formed with the patient supine butwith the knee flexed to 90 degrees(Fig 7). The examiner grasps the tibiajust below the knee joint, with theexaminer’s thumbs placed on eitherside of the patellar tendon. The tibia ispulled forward. An increased amountof anterior tibial translation com-pared with the opposite leg or a lackof a firm end point suggests a tornACL.69 Both the Lachman and anteriordrawer tests require a relaxed patientwithout hamstring guarding.

The pivot shift test is performed withthe patient supine and the knee ex-tended (Fig 8). The examiner stresses

the lateral side of the knee whilegradually flexing the patient’s knee. A“clunk” sensation occurs when thepartly subluxated tibia relocates inrelation to the femur, indicating thatthe ACL is torn. The pivot shift test isoften difficult to perform in the pedi-atric athlete with an acute knee injurybecause of pain and guarding.

The Lachman test is considered themost accurate of the 3 commonlyperformed clinical tests for an acuteACL tear, showing a pooled sensitivityof 85% (95% confidence interval [CI]83–87) and a pooled specificity of94% (95% CI 92–95). The pivot shifttest is very specific, namely 98% (95%CI 96–99), but has a poor sensitivity of24% (95% CI 21–27).68,69 Last, the kneearthrometer is an objective, accurate,and validated tool that measures, inmillimeters, the amount of tibialtranslation relative to the femur whileperforming a Lachman test and, thus,augments the clinical examinationwhen examining a patient with an ACLtear.70,71

Imaging

For the pediatric athlete who presentswith a traumatic knee effusion, plainradiographs should be obtained to ruleout fracture, dislocation, osteochondral

injury, or physeal injury in addition to,or instead of, an ACL tear. MRI is usuallynot necessary to make the diagnosis ofan ACL tear, as a positive Lachman testresult is sufficient. However, in thepediatric patient whose physical ex-amination is difficult to perform be-cause of pain, swelling, and/or lack ofcooperation or if there is concern forassociated injuries or subtle physealfracture, MRI may be a valuable ancil-lary tool.72–76 MRI also can be useful forsurgical planning. Sensitivity andspecificity of MRI for detecting ACLtears in children has been reported tobe 95% and 88%, respectively.76 Formeniscal tears in children, MRI hasbeen reported to be 100% sensitiveand 89% specific.72 One study foundthat the sensitivity, specificity, positivepredictive value, and accuracy of MRIfor identifying all categories of patho-logic changes were lower for pediatric(ages 4–14 years) versus adolescent(ages 15–17 years) patients.75

TREATMENT

The treatment of ACL tears in the pe-diatric athlete is challenging and con-troversial. An ACL tear in a child is nota surgical emergency. Multiple timelydiscussions with the parents and thechild about the appropriate manage-ment options and understanding theirgoals and expectations are very im-portant.73 Surgery is not absolute. Thegeneral indications for surgery includethe patient’s inability to participate inhis or her chosen sport, instability thataffects activities of daily living, and anassociated repairable meniscal tear or aknee injury with multiple torn ligaments.

Treatment of ACL injuries in the skele-tally immature patient remains con-troversial, because standard ACLreconstructions involve the use of drillholes that cross the open physes andmay potentially cause growth distur-bance, such as shortening or angulationof the child’s leg.8 A meta-analysis of 55

FIGURE 6Lachman test. (Reproduced with permission from Harris SS, Anderson SJ, eds. Care of the YoungAthlete. 2nd ed. Elk Grove Village, IL: American Academy of Pediatrics and American Academy ofOrthopedic Surgeons; 2009:413.)

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studies suggested that the risk of leglength difference or angular leg devia-tions was approximately 2% after ACLreconstruction in children and adoles-cents.77 The authors recommendedrandomized controlled trials to clarifythis risk more accurately. Ideally, sur-gical treatment of an ACL tear ina skeletally immature athlete would bepostponed until skeletal maturity, and

the athlete would not develop meniscaltears during that waiting time. In thepast, delay in surgical treatment wasvery common. Orthopedic surgeonsrecommended nonoperative treatment,including a brace, rehabilitation, andsports restriction for many monthsuntil skeletal maturity occurred andtraditional ACL surgery could be per-formed safely.73,78,79 For some pediatric

athletes and parents, conservative man-agement still may be a reasonabletreatment option. However, many pe-diatric athletes and their parents areless inclined to agree to restrict theathlete’s activity. In such cases, an ACLtear in the pediatric athlete treatedconservatively can lead to additional in-stability episodes, meniscal tears, artic-ular cartilage damage, and early-onsetarthritis.80–84 Therefore, most recentliterature now supports early surgeryfor pediatric athletes with an ACL-deficient knee and recurrent episodesof instability.82,85–87 Overall, ACL surgeryis about 90% successful in restoringknee stability and patient satisfaction.88

No consensus exists on the best methodto treat an ACL tear in a pediatric athlete.Safe and effective surgical techniquescontinue to evolve.78 However, the cur-rent literature suggests reasonable,evidenced-based management optionsthat minimize the risks of iatrogenicgrowth plate injury.89 For example, ACLsurgery in a pediatric athlete is oftenperformed via a physeal-sparing tech-nique or a transphyseal technique.86,90–92

The physeal-sparing technique avoidsinjury to the growth plate, but it placesthe graft in a nonanatomic position. Anaccurate understanding of the athlete’sphysical maturity by determining skele-tal age and Tanner stage helps to identifywhich treatment is best for a specificpatient.73,86,87,92–98 The most commonmethod of measuring the patient’s skel-etal age is to compare an anteropos-terior radiograph of the patient’s lefthand and wrist to an age-specific ra-diograph in the Greulich and Pyle at-las.94 Tanner stage can be determinedby self-assessment, which has beenshown to be valid and reliable.99

Patients with open physes at Tannerstage III and skeletal age of less than 14in girls and less than 16 in boys can beoffered the option of activity modifi-cation, functional bracing, rehabilita-tion, and careful follow-up. Surgery is

FIGURE 7Anterior drawer test. (Reproduced with permission from Sarwark JF, ed. Essentials of Musculo-skeletal Care. 4th ed. Rosemont, IL: American Academy of Orthopedic Surgeons; 2010:638.)

FIGURE 8Pivot shift test. (Reproduced with permission from Sarwark JF, ed. Essentials of MusculoskeletalCare. 4th ed. Rosemont, IL: American Academy of Orthopedic Surgeons; 2010:637.)

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indicated in skeletally immature patientswith a torn ACL and an additional re-pairable meniscal injury and in patientswho failed conservative care. In addi-tion, ACL surgery can be elected bypatients unwilling to comply with ac-tivity restrictions and bracing. Parentsand patients who request surgery be-fore maturation of the growth platesshould be counseled about the risk ofangular or longitudinal growth injuryand the possible need for additionalsurgery.16,100–103

Most orthopedic surgeons select asurgical treatment option based onthe patient’s skeletal and physiologicage. For example, in the high-risk, mostskeletally immature athlete (skeletalage less than 11 in girls and less than13 in boys, and Tanner stage I or II) anextraphyseal procedure using a bandof the iliotibial tendon or a hamstringtendon graft passed over the top of thelateral femoral condyle and througha groove in the anterior tibia is a rea-sonable surgical option.15,103–106 Bothof these extraphyseal proceduresavoid the growth plate to prevent therisk of growth disturbance. A thirdoption for the completely immaturepediatric athlete is a more techni-cally demanding all-epiphyseal pro-cedure using hamstring tendon grafts.Some authors have used intraopera-tive 3-dimensional computed tomog-raphy to confirm the precise tunnellocation and minimize risk of physealinjury.89

In the intermediate-risk mid-age child(skeletal age 11 to 14 in girls and 13 to16 in boys, and Tanner stage III or IV), theprevious physeal-sparing methods maybe selected; however, many of theseintermediate-maturity patients are safelyand more appropriately treated withtransphyseal reconstruction using small7- to 8-mm centrally placed drill holesand a soft tissue graft, such as thehamstring tendons or an allograft.106–109

Physeal injury can be minimized by us-

ing a small drill hole and soft tissuegrafts and by placing the fixation awayfrom the physis. Patients and parentsshould be counseled that there remainsa small risk of physeal injury and apossibility of additional surgery forangular or growth disturbance.

Last, adolescents who are approachingskeletal maturity (skeletal age olderthan 14 in girls and older than 16 in boys,Tanner stage V) can undergo anatomicACL surgery with tibial and femoral drillholes and the surgeon’s graft of choicewith minimal risk of physeal injury.82,110,111

Autografts and allografts are bothreasonable graft choices dependingon the patient and surgeon prefer-ences. Autografts have a lower graftfailure rate in 2 studies.112,113

Rehabilitation after ACL surgery mayneed to be modified for the individualpatient and the particular surgicalprocedure. In general, a graduated re-habilitation program emphasizing fullextension; immediate weight bearing;active range of motion; and strength-ening of the quadriceps, hamstrings, hip,and core can be started in the first fewweeks after surgery. Progressive re-habilitation during the first 3 monthsafter surgery includes range-of-motionexercises, patellar mobilization, pro-prioceptive exercises, endurance train-ing, and closed-chain strengtheningexercises. Straight-line jogging, plyo-metric exercises, and sport-specificexercises are added after 4 to 6months. Return to play typically occurs 7to 9 months after surgery.

Return to Sport

Studies of competitive athletes, mostof whom were older than 18 years, ina variety of sports have demonstratedthat 78% to 91% returned to sportsparticipation after ACL reconstruc-tion.114 However, only 44% to 62%returned to their previous level ofathletic performance.114–119 Femaleathletes were less likely than male

athletes to return to sports after ACLinjury or ACL reconstruction.19,119,120

ACL INJURY PREVENTION

Bracing

It is unlikely that prophylactic bracingcan decrease the risk of ACL injury. Therelative effects of 6 different bracedesigns on anterior tibial translationand neuromuscular function were stud-ied in chronically unstable ACL-deficientpatients.121 Bracing decreased ante-rior tibial translation in the range of30% to 40% without the stabilizingcontractions of the hamstrings, quad-riceps, or gastrocnemius muscles. Withmuscle activation and bracing, anteriortibial translation was decreased be-tween 70% and 85%. However, thebraces slowed hamstring muscle re-action times. A brace with a 5-degreeextension stop decreased extensionon landing.122

Functional bracing after ACL re-construction has been studied usingrandomized controlled cohorts placedinto braced or nonbraced groups.123 Thebraced group was instructed to weara functional knee brace for all cutting,pivoting, or jumping activities for thefirst year after ACL reconstruction.There were no differences betweengroups in knee stability, functionaltesting, subjective knee scores, andrange of motion or strength testing,and the investigators concluded thatpostoperative bracing did not changeoutcomes. Data are insufficient at thistime to determine whether functionalbracing decreases the risk of ACL injuryor reinjury. Knee bracing does not im-prove functional performance of sub-jects after ACL reconstruction and mayactually reduce running and turningspeed.124

Neuromuscular Training Programs

Although ACL injuries occur too quick-ly for reflexive muscular activation,

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athletes can adopt or “preprogram”safer movement patterns that reduceinjury risk during landing, pivoting, orunexpected loads or perturbationsduring sports movements.54,60 Withsufficient neuromuscular control ofknee position to avoid dynamic valgus,knee stability may be improved duringcompetitive sport and the risk of ACLinjury can be significantly reduced. Acollection of prospective cohort studiesand randomized controlled trials haveexamined the effect of neuromusculartraining programs on ACL, knee, andother lower-extremity injuries in soc-cer, basketball, volleyball, and handball(Fig 9).22,125–137 Some studies used only1 or 2 types of exercises, such asplyometric exercises and/or balanceexercises, and others applied a morecomprehensive approach by includingplyometrics (repetitive jumping exer-cises designed to build lower-extremitystrength and power), strengthening,stretching, and balance training.

Systematic examination of the dataextracted from these studies leads toa few potentially valuable general-izations.138–140 Plyometric training com-bined with technique training andfeedback to athletes regarding properform were the common components ofprograms that effectively reduced ACLinjury rates. Balance training alone maynot be sufficient to reduce ACL injuryrisk. Although some of the effectiveprograms did not include strengthtraining, those that did were among themost effective at decreasing ACL injuryrates. ACL injury reduction was greatestfor soccer athletes, and combined pre-and in-season training was more ef-fective than pre- or in-season trainingalone. With respect to age, the greatestreduction in injury risk was demon-strated for female athletes in their mid-teens (14–18 years) compared withthose in their late teens (18–20 years)and adults (>20 years), with 72% riskreduction for those <18 years of age

and 16% risk reduction for those ≥18years of age. This suggests the bestwindow of opportunity for ACL injuryrisk reduction may be during early pu-bertal maturation, at or just beforegirls’ neuromuscular risk factors startto become evident and ACL injury ratesin girls dramatically increase. It is un-known whether neuromuscular trainingor other interventions can modulate theincreased risk of early-onset degene-rative knee arthritis after ACL injury.141

More information about specific evidence-based neuromuscular training programscan be found in the respective articlesdescribing their study results.125–137 Inaddition, the AAP has compiled a se-ries of evidence-based resources thatinclude instructional videos for pedi-atricians, athletes, and coaches whowould like to learn more about neu-romuscular training and how to per-form the preventive exercises (http://www.aap.org/cosmf).

CONCLUSIONS AND GUIDANCE FORCLINICIANS

1. The number of ACL injuries in youngathletes has increased over thepast 2 decades, coincident withthe growing number of childrenand adolescents participating in or-

ganized sports, intensive sportstraining at an earlier age, andgreater rate of diagnosis becauseof increased awareness and greateruse of advanced medical imaging.

2. Intrinsic risk factors for ACL in-jury include higher BMI, subtalarjoint overpronation, generalizedligamentous laxity, and decreasedneuromuscular control of thetrunk and lower extremities.

3. ACL injury rates are low in youngchildren and increase sharply dur-ing puberty, especially for girls,who have higher rates of ACL inju-ries than boys do in similar sports.

4. Although there likely are multiple fac-tors underlying the differences innoncontact ACL injury rates in maleand female athletes, neuromuscularcontrol may be the most importantand most modifiable factor.

5. ACL injuries often require surgeryand/or many months of rehabilita-tion and substantial time lost fromschool and sports participation.

6. The best physical examination testfor an ACL tear is the Lachman test.

7. MRI can be valuable for diagnos-ing ACL tears and associatedmeniscal and chondral injury in

FIGURE 9Reduction of noncontact ACL injury with neuromuscular training. (Reproduced with permission fromMyer GD, Sugimoto D, Thomas S, Hewett TE. The influence of age on the effectiveness of neuromusculartraining to reduce anterior cruciate ligament injury in female athletes: a meta-analysis. Am J SportsMed. 2013;41(1):209.138)

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the pediatric athlete whose phys-ical examination is difficult to per-form because of pain, swelling,and lack of cooperation.

8. An ACL tear in a youth athlete isnot a surgical emergency. Multiplediscussions with the athlete and par-ents may be needed to understandthe athlete’s goals and parental ex-pectations and to educate the fam-ily about possible treatment options.

9. The patient’s skeletal age, measuredby an anteroposterior radiograph ofthe left hand and wrist, and Tannerstage are helpful for the physicianin deciding the most appropriatetreatment of an ACL tear in a skele-tally immature athlete.

10. Pediatricians and orthopedic sur-geons treating young people withACL injuries should advise themthat regardless of treatment choice,they are at increased risk of early-onset osteoarthritis in the injuredknee. Such discussions should beappropriately documented in thepatient’s medical record.

11. Musculoskeletal changes that de-crease dynamic joint stability inhigh-risk female athletes and po-tentially lead to higher injury ratesin this population could be modifiedif neuromuscular training interven-tions are instituted in early-middleadolescence, when the neuromus-cular risk factors for ACL injurystart to develop.

12. Neuromuscular training appears toreduce the risk of injury in adoles-

cent female athletes by 72%. Pre-vention training that incorporatesplyometric and strengthening exer-cises, combined with feedback toathletes on proper technique, ap-pears to be most effective.

13. Pediatricians and orthopedic sur-geons should direct patients athighest risk of ACL injuries (eg, ad-olescent female athletes, patientswith previous ACL injury, general-ized ligamentous laxity, or familyhistory of ACL injury) to appropri-ate resources to reduce their injuryrisk (http://www.aap.org/cosmf).Such discussions also should beappropriately documented in thepatient’s medical record.

14. Pediatricians and orthopedic sur-geons who work with schools andsports organizations are encour-aged to educate athletes, parents,coaches, and sports administra-tors about the benefits of neuro-muscular training in reducing ACLinjuries and direct them to appro-priate resources (http://www.aap.org/cosmf).

LEAD AUTHORSCynthia R. LaBella, MD, FAAPWilliam Hennrikus, MD, FAAPTimothy E. Hewett, PhD, FACSM

COUNCIL ON SPORTS MEDICINE ANDFITNESS EXECUTIVE COMMITTEE,2012–2013Joel S. Brenner, MD, MPH, FAAP, ChairpersonAlison Brooks, MD, MPH, FAAPRebecca A. Demorest, MD, FAAPMark E. Halstead, MD, FAAP

Amanda K. Weiss Kelly, MD, FAAPChris G. Koutures, MD, FAAPCynthia R. LaBella, MD, FAAPMichele LaBotz, MD, FAAPKeith J. Loud, MDCM, MSc, FAAPStephanie S. Martin, MD, FAAPKody A. Moffatt, MD, FAAP

PAST COUNCIL EXECUTIVECOMMITTEE MEMBERSHolly J. Benjamin, MD, FAAPCharles T. Cappetta, MD, FAAPTeri McCambridge, MD, FAAP

LIAISONSAndrew J. M. Gregory, MD, FAAP – AmericanCollege of Sports MedicineLisa K. Kluchurosky, MEd, ATC – National AthleticTrainers AssociationJohn F. Philpot, MD, FAAP – Canadian PediatricSocietyKevin D. Walter, MD, FAAP – National Federationof State High School Associations

CONSULTANTTimothy Hewett, PhD

STAFFAnjie Emanuel, MPH

SECTION ON ORTHOPEDICS EXECUTIVECOMMITTEE, 2012–2013Richard M. Schwend, MD, FAAP, ChairpersonJ. Eric Gordon, MD, FAAPNorman Y. Otsuka, MD, FAAPEllen M. Raney, MD, FAAPBrian A. Shaw, MDBrian G. Smith, MDLawrence Wells, MD

PAST SECTION EXECUTIVE COMMITTEEMEMBERWilliam L. Hennrikus, MD, FAAP, Immediate PastChairperson

STAFFS. Niccole Alexander, MPP

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SPORTS MEDICINE AND FITNESS, and SECTION ON ORTHOPAEDICSCynthia R. LaBella, William Hennrikus, Timothy E. Hewett and COUNCIL ONAnterior Cruciate Ligament Injuries: Diagnosis, Treatment, and Prevention

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