ARTICLEPEDIATRICS Volume 139 , number 3 , March 2017 :e 20161877

ACL Tears in School-Aged Children and Adolescents Over 20 YearsNicholas A. Beck, MD, a J. Todd R. Lawrence, MD, PhD, b James D. Nordin, MD, MPH, c Terese A. DeFor, MS, c Marc Tompkins, MDd

abstractBACKGROUND: Anterior cruciate ligament (ACL) tears are thought to occur with increasing

frequency in young patients. No study has shown increased incidence over time. We

hypothesized the incidence of ACL tears in young patients has increased over the past 20

years.

METHODS: This descriptive epidemiology study is a retrospective review of insurance billing

data of all patients aged 6 to 18 years with Current Procedural Terminology, Fourth Revision

codes for ACL tear and reconstruction or International Classification of Diseases, Ninth

Revision, Clinical Modification codes from 1994 to 2013. Injuries were normalized to

persons per year enrolled in the insurance database based on age and sex. Analysis was

performed based on sex and age (6–14, 15–16, and 17–18 years).

RESULTS: The rate of ACL tears per 100 000 person-years averaged 121 ± 19 (range 92–151).

All trends increased significantly except for the male 6- to 14-year-old and 17- to 18-year-

old age groups. Overall there was an annual increase of 2.3%. Females had significantly

higher incidence except in the 17- to 18-year-olds. Females peaked at age 16 years and

males at age 17 years, with rates of 392 ACL tears and 422 ACL tears per 100 000 person-

years, respectively.

CONCLUSIONS: The incidence of ACL tears in pediatric patients increased over the last 20

years. Females were at higher risk except in the 17- to 18-year -old group. Peak incidence

is noted during high school years. These data help target the most at-risk patients for ACL

prevention programs.

aUniversity of Minnesota, Minneapolis, Minnesota; bChildren’s Hospital of Philadelphia, Philadelphia,

Pennsylvania; cHealthPartners, Minneapolis, Minnesota; and dTRIA Orthopaedic Center, Bloomington, Minnesota

Dr Beck conceptualized and helped design the study, drafted the initial manuscript, and edited

the fi nal manuscript; Dr Lawrence conceptualized and helped design the study and reviewed

and revised the manuscript; Dr Nordin helped design the study and reviewed and revised the

manuscript; Mrs DeFor collected the data, carried out the initial analyses, and reviewed and

revised the manuscript; Dr Tompkins conceptualized and helped design the study, acted as the

senior author, and reviewed and revised the manuscript; and all authors approved the fi nal

manuscript as submitted.

DOI: 10.1542/peds.2016-1877

Accepted for publication Dec 20, 2016

Address correspondence to Nicholas A. Beck, MD, 2450 Riverside Ave South, Suite R200,

Minneapolis, MN 55454. E-mail: beckx481@umn.edu

PEDIATRICS (ISSN Numbers: Print, 0031-4005; Online, 1098-4275).

Copyright © 2017 by the American Academy of Pediatrics

FINANCIAL DISCLOSURE: The authors have indicated they have no fi nancial relationships relevant

to this article to disclose.

FUNDING: Funds provided by the University of Minnesota Clinical Research Committee.

To cite: Beck NA, Lawrence JTR, Nordin JD, et al. ACL Tears

in School-Aged Children and Adolescents Over 20 Years.

Pediatrics. 2017;139(3):e20161877

WHAT’S KNOWN ON THIS SUBJECT: Recent reports

of anterior cruciate ligament (ACL) injuries in

young patients suggest the incidence is increasing.

However, true incidence data are scarce. Female

patients are at higher risk of ACL injury than males

participating in similar activities.

WHAT THIS STUDY ADDS: We present incidence data

for ACL tears in young patients and show that the

incidence increased over the past 20 years. Girls

exhibit higher risk until age 17. The ages most at risk

are 16 for girls and 17 for boys.

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BECK et al

Midsubstance tears of the anterior

cruciate ligament (ACL) were

classically thought to be rare injuries

in young patients, with tibial spine

avulsion fractures supposedly

representing the equivalent injury in

patients with open physes. 1 Others

have noted that ACL tears seem to be

presenting with greater frequency

in pediatric patients, including

patients as young as 5 years

old. 1 – 6 The increase in ACL surgical

consultations in young patients has

been attributed to multiple factors,

including increased participation in

high-demand year-round sports at an

earlier age, better clinician awareness

and recognition of the signs and

symptoms of ACL tears, increased

female athletic participation, and

the expanded role of magnetic

resonance imaging in the diagnosis

of intra-articular knee pathology. 1, 7, 8

Identifying these injuries may

be important to avoid additional

intra-articular knee injuries and

chondral damage through activity

modification or recently developed

surgical reconstruction techniques

that minimize or avoid physeal

damage. 9 –13

Most studies of ACL injury rates

report on adult athletes or military

personnel. 4, 14 – 21 Large population-

based epidemiologic studies often

group young patients together and

report very low rates of ACL injuries

in school-aged patients, and none to

our knowledge have looked at the

change in incidence over time.22, 23

Thus, the goal of this study was to

review the billing database of a large

metropolitan insurance network to

determine whether the number of

ACL tears has increased over the past

20 years. We also sought to examine

differences between sex, age, and

delay in surgery over the study

period. We hypothesized that there

would be an increase in the incidence

of ACL tears in patients ≤18 years

of age over the past 20 years, with

female patients showing a higher rate

of increase than male patients.

METHODS

A retrospective review of insurance

billing data in a large metropolitan

network was performed for all

children and adolescents aged

6 to 18 years with International

Classification of Diseases, Ninth

Revision, Clinical Modification

(ICD-9-CM) codes for ACL tears and

Current Procedural Terminology,

Fourth Revision (CPT-4) codes for

ACL reconstruction from January

1994 to December 2013. Patients

were included if they had ≥2

occurrences of ACL diagnosis

codes (844.2 or 717.83) on medical

claims ≤4 months apart, or ≥1

ACL procedure codes (29888)

during the study period. Therefore,

all patients with ACL tears were

included, not just those with surgical

reconstruction. Multiple ACL injuries

per patient were counted if >4

months elapsed between diagnoses.

Patients were excluded if they were

outside the included age ranges, if

the first diagnosis code was outside

a member’s enrollment period, or if

they had only 1 ICD-9-CM code.

Analysis included year-by-year

total incidence of ACL injury and a

breakdown by sex and ages grouped

6 to 14 years, 15 to 16 years, and

17 to 18 years. Denominators were

normalized to patients per year

enrolled in the insurance database

based on age and sex to calculate

rates per 100 000 person-years

specific to that cohort. Because

we used the insurance network,

all patients in the network were

captured by the insurance data

search. In addition, because we

queried it on a yearly basis, we were

able to control for patients entering

and leaving the insurance network.

Delay in surgery was calculated by

time between first ICD-9-CM code

and Current Procedural Terminology

code for each ACL injury. The annual

percent of ACL tears surgically

reconstructed was calculated.

The trend of annual incidence

for each age and sex cohort was

tested for significance with Poisson

regression analysis. Logistic

regression was used to look for

significant change in annual surgery

rates. Linear regression was used

to look for significant change in the

delay in surgery. Differences between

sexes were tested with Poisson

regression analysis for change in

annual incidence and for differences

in overall and age-specific rates.

RESULTS

Total patients enrolled in the

insurance database within our study

age range averaged 136 000 ± 15 000

per year, with approximately an

even number of male and female

patients each year. A total of 3303

ACL tears were identified over the

study period, 1584 (48%) ACL tears

in male patients and 1719 (52%) in

female patients. The overall annual

incidence of ACL tears averaged

121 ± 19 (range 92–151) per 100 000

person-years (or 0.121%) ( Fig 1

and Table 1). The incidence in male

patients averaged 114 ± 22 (range

83–160) per 100 000 person-years

(or 0.114%). The incidence in female

patients averaged 129 ± 24 (range

98–184) per 100 000 person-years

(or 0.129%). The breakdown by

age groups over time for overall

patients, male patients, and female

patients is shown in Figs 2, 3, and 4,

respectively.

The incidence of ACL tears by age

overall is shown in Fig 5. Poisson

regression analysis indicated that

differences in incidence between

male and female patients by age

were statistically significant for

each age category (P < .001).

Female patients peaked at age 16

years with an incidence of 392 ACL

tears per 100 000 person-years (or

0.392%), and male patients peaked

at age 17 years with an incidence of

422 ACL tears per 100 000 person-

years (or 0.422%). We found no

significant difference between

the amount of change in ACL tear

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PEDIATRICS Volume 139 , number 3 , March 2017 3

FIGURE 1Rates of ACL tears per 100 000 person-years for the overall male and female groups over the 20-year study period.

TABLE 1 Rates per 100 000 Person-Years for the Overall Male and Female Groups Over the 20-y Study Period

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

Female

rate

per

100 000

117 113 109 98 118 107 118 127 99 110 131 143 120 127 142 133 167 184 176 131 140

Male rate

per

100 000

122 90 99 87 83 98 119 103 85 119 88 132 132 130 160 134 127 118 117 145 82

FIGURE 2Rates of ACL tears per 100 000 person-years for male and female patients broken down by age groups over the 20-year study period.

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incidence over time between male

and female patients overall

(P = .6) and across the age groups

(P = .2); however, overall incidence

was significantly higher in female

patients (129 ACL tears per 100 000

person-years vs 114 ACL tears per

100 000 person-years; P < .001)

and in the 6- to 14-year-old (33 ACL

tears per 100 000 person-years vs

26 ACL tears per 100 000 person-

years; P < .01) and 15- to 16-year-

old (371 ACL tears per 100 000

person-years vs 250 ACL tears per

100 000 person-years; P < .001) age

groups over our study period. Male

patients had significantly higher

incidence in the 17- to 18-year-

old age group (394 ACL tears per

100 000 person-years vs 337 ACL

tears per 100 000 person-years;

P < .01).

Results of the calculated changes in

incidence over time are summarized

in Table 2. All analyzed trends

increased significantly over time

except for the male 6- to 14-year-

olds and male 17- to 18-year-olds.

Overall we found that the number

of ACL tears per 100 000 person-

years increased 2.3% per year. Male

patients had an increase of 2.2%

per year, and female patients had

an increase of 2.5% per year. The

subgroup with the highest increase

was female 15- to 16-year-olds,

whose incidence increased 2.6% per

year.

4

FIGURE 3Rates of ACL tears per 100 000 person-years for the male patients broken down by age groups over the 20-year study period.

FIGURE 4Rates of ACL tears per 100 000 person-years for the female patients broken down by age groups over the 20-year study period.

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PEDIATRICS Volume 139 , number 3 , March 2017

Logistic regression showed that the

percentage of ACL tears surgically

reconstructed significantly increased

(P < .001) ( Fig 6 and Table 3), and

linear regression analysis identified

a significant increase in the delay to

surgery over the study period

(P = .04) ( Fig 7 and Table 4).

DISCUSSION

Through analysis of insurance data on

a captured population of patients, we

were able to calculate true incidence

numbers for a large metropolitan

population of pediatric patients. Over

the 20 years analyzed, we found a

2.3% annual increase in the number

of ACL tears in patients aged 6 to 18

years. Female patients had significantly

higher rates of injury in the younger

ages, but in the 17- to 18-year-old age

group male patients had a significantly

higher incidence. Subgroup analysis

showed that female patients in all 3

age groups had a significant increase

in incidence of ACL tears over the

study period, whereas only the male

patients aged 15 to 16 years had an

increased incidence. We also found

that the percentage of ACL injuries

surgically reconstructed increased, and

the average time from injury to surgery

increased significantly over our study

period.

This study is the first of its kind to

identify an increase in the incidence

of ACL tears in young patients over

the last 20 years. These data are novel

in that they report incidence of ACL

injury within a known, closed cohort.

Data were obtained on a yearly basis,

so the insurance database allows

for correction of patients entering

and leaving the insurance plan. In

addition, using the insurance database

means data are not restricted to a

single institution because the ACL tear

could be diagnosed in >1 location,

or the surgery could be performed

in a separate location, and all of

this information would be captured

within the insurance database. These

measures should add to a more

complete understanding of what we

have suspected in terms of increases

in pediatric ACL injury over time.

5

FIGURE 5Rates of ACL tears per 100 000 person-years for male and female patients over the study period broken down by age.

TABLE 2 Change per Year for Each Analysis, With Confi dence Intervals

Data Group Change per Year, % 95% Confi dence Interval, %

All ages

Female and male patients 2.3 1.7 to 2.9

Female patients 2.5 1.6 to 3.3

Male patients 2.2 1.3 to 3.0

Breakdown by age

Female and male patients

6- to 14-y-olds 2.1 0.70 to 3.6

15- to 16-y-olds 2.5 1.6 to 3.5

17- to 18-y-olds 1.3 0.40 to 2.2

Female patients

6- to 14-y-olds 2.5 0.50 to 4.5

15- to 16-y-olds 2.6 1.4 to 3.9

17- to 18-y-olds 1.5 0.10 to 2.8

Male patients

6- to 14-y-olds 1.8 −0.30 to 3.9

15- to 16-y-olds 2.4 0.90 to 3.9

17- to 18-y-olds 1.2 −0.04 to 2.4

Percentage reconstructed 3.0 2.0 to 4.0

Time to reconstruction 0.90 0.03 to 1.8

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FIGURE 6Percentage of ACL tears surgically reconstructed by year over the 20-year study period.

TABLE 3 Percentage of ACL Tears Surgically Reconstructed by Year Over the 20-y Study Period

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

Percentage

ACL tears

surgically

repaired

57 65 70 57 66 68 73 80 69 73 74 74 78 70 77 70 70 76 75 73 70

FIGURE 7Median delay in days to surgical reconstruction for patients treated surgically over the 20-year study period.

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PEDIATRICS Volume 139 , number 3 , March 2017

The average annual incidence of

ACL injuries found in our study

(0.12%) is similar to those found

in large population-based studies.

Nordenvall et al 23 used data from the

Swedish National Patient Register

to estimate the sex- and age-specific

incidence of ACL tears in Sweden.

They found the average annual

incidence to be 78 per 100 000

inhabitants (or 0.078%). Very few

injuries were found in patients <10

years old, and the incidence was

similar in male and female patients

in the 11- to 20-year-old age group

of 144 per 100 000 inhabitants (or

0.14%). Gianotti et al 22 reported

data from New Zealand’s Accident

Compensation Corporation showing

a similar breakdown of incidence

by age and sex. They also showed

very few ACL injuries in patients <10

years old. Their incidence in 15- to

19-year-olds was between 65 and

100 per 100 000 person-years for

female and male patients respectively

(or 0.065%–0.10%).

It is important to note that previous

studies define rates of injury in

different units. Studies looking at risk

for ACL injuries in athletes or military

personnel present their rates based

on exposure-based denominators to

the sport or activity by either hours

or season. Population-based studies

often define rates based on absolute

time-based denominators such as

incidence per 100 000 person-years.

Moses et al 24 attempted to compare

multiple studies by converting

incidence rates in exposure-based

studies to annual units. They found

studies reporting population

incidence with a low annual median

incidence of 0.03%. Studies of

ACL injury data from military and

professional sports showed much

higher annual incidences of up to

2.14% and 3.67%, respectively.

Dodwell et al 25 showed an increase

in the rate of ACL reconstructions

performed on pediatric (defined as

ages 3 to 20 years old) patients in

New York State from 1990 to 2009.

In their study, population estimates

from the US Census Bureau were

used as the denominator to obtain

rates per 100 000 population.

They found that the rate rose

from 17.6 ACL reconstructions

per 100 000 population in 1990

to 50.9 ACL reconstructions per

100 000 population in 2009, or a

190% increase over their study

period. This compares to the more

modest 2.3% yearly increase in our

population. Their analysis by sex

found that male patients had a 15%

higher rate of ACL reconstructions,

where our study showed higher

rates in female patients except for

the 17- to 18-year-old patients.

Lively and Feathers 17 found an

increasing incidence of ACL injuries

in a collegiate population based on

incoming athletes’ injury history

at a single institution from 1996 to

2008. An athlete had a 2.7 greater

odds of having a previous ACL injury

in 2008 than those who arrived in

1996. Although their analysis showed

a nearly linear increasing trend

by year, there was no significant

correlation with sport (P = .41) or sex

(P = .71).

In this study, female patients on

average had a higher incidence

overall and across the 6- to 14-year-

old and 15- to 16-year-old age groups

than their male counterparts. ACL

injury rates have been shown in

multiple studies to be 2 to 8 times

higher in female than male patients

when comparing exposure to sex-

comparable sports. 4, 14, 20 Reasons

for this observed difference are

thought to be related factors such as

geometry of the intercondylar notch

and smaller size of ACL, as well as

biomechanical and neuromuscular

factors such as higher quadriceps-to-

hamstring ratio and landing from a

jump with less hip and knee flexion

and more hip adduction, leading to

increased dynamic knee valgus with

greater knee abduction angles. 26 It is

interesting that male patients in the

17- to 18-year-old age group of our

study surpassed female patients, with

significantly higher rates. Proposed

explanations for this observation

include higher intensity of collision

sports in older male athletes, fewer

female adolescents participating in

sports at this age, and female athletes

prone to ACL injury having already

sustained injuries and no longer

competing.

Through subgroup analysis by age

and sex, we attempted to identify the

most at-risk patients over our study

period. Much effort has recently

been put forth in the sports medicine

community to develop prevention

programs with neuromuscular and

proprioceptive training, especially for

female athletes. 26 Noyes and Barber-

Westin 27 conducted a systematic

review of 8 neuromuscular retraining

studies in female athletes. Three

studies found a significant reduction

7

TABLE 4 Median Delay in Days to Surgical Reconstruction for Patients Treated Surgically Over the 20-y Study Period

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

Median delay in

days to surgical

reconstruction

for patients

treated

surgically

26 29 26 31 28 24 33 28 31 34 27.5 32 26 31 28 30 27.5 26 23 25 23

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in the number of noncontact

ACL injuries, with a relative risk

reduction ranging from 75% to

100%. The remaining 5 studies

found no significant decrease with

their programs; however, the overall

ACL injury rates in these studies

were much lower. There was a large

discrepancy in how the programs

were performed, based on the

frequency, duration, supervision, and

compliance. Myer et al 28 performed

a meta-analysis of neuromuscular

training studies, specifically looking

at the effectiveness the programs

for different age participants. They

included 14 clinical trials and found

a significant age-related reduction

in injury rate, with an odds ratio of

0.28 in the 14- to 18-year-old female

athletes, compared with an odds ratio

of 0.48 in the 18- to 20-year-olds and

1.01 in the >20-year-olds. Thus the

programs seem to be more effective

in younger patients. In our cohort, all

subgroups of the female patients and

the male 15- to 16-year-old subgroup

showed a significant increase in ACL

injury incidence over time. Because

the injury rates in these cohorts seem

to be increasing, they may also be

the most likely to benefit from injury

prevention programs.

Two additional findings of this study

are that the percentage of injuries

surgically reconstructed increased

and the average time to surgery

increased over our study period,

although the time to surgery increase

was small (<1%) and clinically

insignificant. A traditional treatment

approach for ACL injuries in young

patients has been to attempt a trial

of conservative treatment until the

child is close to the end of growth,

based on the assumption that the

risk of limb length discrepancy

and angular growth disturbances

decreases as the patient approaches

skeletal maturity. 1, 3, 7, 29 Recent

studies have shown poor outcomes

with nonoperative treatment.

Lawrence et al11 showed that

delaying surgery of a complete ACL

tear for >12 weeks correlated with

a significant increase in the number

of irreparable medial meniscal tears

and lateral compartment chondral

injuries. Because of this risk, multiple

new surgical techniques have been

developed that range from physeal-

sparing, to partial transphyseal, to

complete transphyseal reconstruction

with smaller, more vertical tunnels. 1

Studies reporting on these techniques

are small retrospective cohorts,

and the procedures are technically

demanding, but the outcomes are

encouraging. Our data suggest that

because of the encouraging results

in the recent literature, surgeons

are more confident treating these

injuries with surgical reconstruction

at younger ages.

Our study has several limitations.

The data were pulled from a specific

regional geographic insurance

database. Therefore, the injury

and surgical treatment rates may

reflect regional differences and

thus may not be representative of

other areas of the United States

or in other countries. The people

covered under this insurance plan

also probably represent people

of a certain socioeconomic class.

Patients with a different quality of

insurance or no insurance may have

more or less exposure to at-risk

activities and higher barriers to

access of care, which may affect the

overall incidence rate. The insurance

database itself has limitations.

We attempted to identify repeat

injuries in patients who have a new

diagnosis code after 4 months, and

this assumption fails to include

new injuries that occur in the first

4 months after return to sport. For

patients with multiple injuries, we

were unable to distinguish between

primary tear of the contralateral

knee and a recurrent tear of the

originally injured knee. In addition,

patients with ACL injuries could

have been missed by entering or

leaving the health insurance plan

before getting the 2 ICD-9-CM

codes required for inclusion, so the

incidence may actually be higher

than that which is reported here.

Despite these limitations, this is the

first study quantifying and showing

an increase in the incidence of ACL

tears in school-aged children and

adolescents.

CONCLUSIONS

This study is the first to show that the

incidence of ACL tears in pediatric

patients (age 6 to 18 years) has

significantly steadily increased by

about 2.3% annually over the last

20 years. Female patients in all age

categories and male patients in the

15- to 16-year-old category showed

the greatest increases and accounted

for most of the overall increase. Both

male and female adolescents have a

peak incidence during high school

years (age 16 years for female and

17 years for male adolescents).

Future studies identifying the

mechanism of injury in young

patients will be helpful for proposing

prevention training.

8

POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential confl icts of interest to disclose.

ABBREVIATIONS

ACL:  anterior cruciate ligament

ICD-9-CM:  International

Classification of

Diseases, Ninth

Revision, Clinical

Modification

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PEDIATRICS Volume 139 , number 3 , March 2017

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