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Anterior Cruciate Ligament and Knee Injury Prevention Programs for Soccer Players: A Systematic Review and Meta-analysis

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Soccer has one of the highest incidences of anterior cruciate ligament (ACL) injuries for both males and females. Several injury prevention programs have been developed to address this concern. However, an analysis of the pooled effect has yet to be elicited. To conduct a systematic review and meta-analysis of ACL and knee injury prevention programs for soccer players, assess the heterogeneity among the studies, and evaluate the reported effectiveness of the prevention programs. Systematic review and meta-analysis. A systematic search of the literature was conducted on PubMed (Medline), Embase, CINAHL, and Central-Cochrane Database. Studies were limited to randomized controlled trials (RCTs) of injury prevention programs specific to the knee and/or ACL in soccer players. The Cochrane Q test and I (2) index were independently used to assess heterogeneity among the studies. The pooled risk difference, assessing knee and/or ACL injury rates between intervention and control groups, was calculated by random-effects models with use of the DerSimonian-Laird method. Publication bias was assessed with a funnel plot and Egger weighted regression technique. Nine studies met the inclusion criteria as RCTs. A total of 11,562 athletes were included, of whom 7889 were analyzed for ACL-specific injuries. Moderate heterogeneity was found among studies of knee injury prevention (P = .041); however, there was insignificant variation found among studies of ACL injury prevention programs (P = .222). For studies of knee injury prevention programs, the risk ratio was 0.74 (95% CI, 0.55-0.89), and a significant reduction in risk of knee injury was found in the prevention group (P = .039). For studies of ACL injury prevention programs, the risk ratio was 0.66 (95% CI, 0.33-1.32), and a nonsignificant reduction in risk of ACL injury was found in the prevention group (P = .238). No evidence of publication bias was found among studies of either knee or ACL injury prevention programs. This systematic review and meta-analysis of ACL and knee injury prevention program studies found a statistically significant reduction in injury risk for knee injuries but did not find a statistically significant reduction of ACL injuries. © 2014 The Author(s).
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Medicine
The American Journal of Sports
http://ajs.sagepub.com/content/early/2014/11/27/0363546514556737
The online version of this article can be found at:
DOI: 10.1177/0363546514556737
published online December 1, 2014Am J Sports Med
Nathan L. Grimm, John C. Jacobs, Jr, Jaewhan Kim, Brandon S. Denney and Kevin G. Shea
Review and Meta-analysis
Anterior Cruciate Ligament and Knee Injury Prevention Programs for Soccer Players: A Systematic
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by KEVIN SHEA on May 16, 2015ajs.sagepub.comDownloaded from by KEVIN SHEA on May 16, 2015ajs.sagepub.comDownloaded from
Anterior Cruciate Ligament and
Knee Injury Prevention Programs
for Soccer Players
A Systematic Review and Meta-analysis
Nathan L. Grimm,
*
y
MD, John C. Jacobs Jr,
z
BS, Jaewhan Kim,
§
PhD,
Brandon S. Denney,
z
BS, and Kevin G. Shea,
||
MD
Investigation performed at the Duke University Medical Center, Durham, North Carolina, USA
Background: Soccer has one of the highest incidences of anterior cruciate ligament (ACL) injuries for both males and females.
Several injury prevention programs have been developed to address this concern. However, an analysis of the pooled effect has
yet to be elicited.
Purpose: To conduct a systematic review and meta-analysis of ACL and knee injury prevention programs for soccer players,
assess the heterogeneity among the studies, and evaluate the reported effectiveness of the prevention programs.
Study Design: Systematic review and meta-analysis.
Methods: A systematic search of the literature was conducted on PubMed (Medline), Embase, CINAHL, and Central-Cochrane
Database. Studies were limited to randomized controlled trials (RCTs) of injury prevention programs specific to the knee and/or
ACL in soccer players. The Cochrane Qtest and I
2
index were independently used to assess heterogeneity among the studies.
The pooled risk difference, assessing knee and/or ACL injury rates between intervention and control groups, was calculated by
random-effects models with use of the DerSimonian-Laird method. Publication bias was assessed with a funnel plot and Egger
weighted regression technique.
Results: Nine studies met the inclusion criteria as RCTs. A total of 11,562 athletes were included, of whom 7889 were analyzed
for ACL-specific injuries. Moderate heterogeneity was found among studies of knee injury prevention (P= .041); however, there
was insignificant variation found among studies of ACL injury prevention programs (P= .222). For studies of knee injury prevention
programs, the risk ratio was 0.74 (95% CI, 0.55-0.89), and a significant reduction in risk of knee injury was found in the prevention
group (P= .039). For studies of ACL injury prevention programs, the risk ratio was 0.66 (95% CI, 0.33-1.32), and a nonsignificant
reduction in risk of ACL injury was found in the prevention group (P= .238). No evidence of publication bias was found among
studies of either knee or ACL injury prevention programs.
Conclusion: This systematic review and meta-analysis of ACL and knee injury prevention program studies found a statistically
significant reduction in injury risk for knee injuries but did not find a statistically significant reduction of ACL injuries.
Keywords: anterior cruciate ligament injury prevention; knee injury; injury prevention; meta-analysis; systematic review
Soccer is the most popular sport in the world, with approx-
imately 265 million players as of 2006.
1
The sport has seen
tremendous growth over the past decade in the United
States, especially in the youth and female populations,
which has led to an associated increase in injuries sus-
tained by soccer players.
2,11
The lower extremity repre-
sents a majority of soccer injuries in both male and
female athletes, with the knee being a frequently injured
body part.
8,36,46
In particular, female athletes have a 3 to
5 times higher risk of serious knee injury compared with
male athletes for soccer, basketball, volleyball, and other
sports.
3-5,11,37
Many intervention programs have been designed
to reduce the risk of injury to the knee and anterior
*
Address correspondence to Nathan L. Grimm, MD, Department of
Orthopaedic Surgery, Duke University Medical Center, 8 Intuition Circle,
Durham, NC 27705, USA (e-mail: nathan.grimm@duke.edu).
y
Department of Orthopaedic Surgery, Duke University Medical Cen-
ter, Durham, North Carolina, USA.
z
University of Utah School of Medicine, Salt Lake City, Utah, USA.
§
Division of Public Health, Study Design, & Biostatistic Center, Univer-
sity of Utah School of Medicine, Salt Lake City, Utah, USA.
||
St Luke’s Intermountain Orthopaedics, Boise, Idaho, USA.
The authors declared that they have no conflicts of interest in the
authorship and publication of this contribution.
The American Journal of Sports Medicine, Vol. XX, No. X
DOI: 10.1177/0363546514556737
Ó2014 The Author(s)
1
Team Physician’s Corner
AJSM PreView, published on December 1, 2014 as doi:10.1177/0363546514556737
by KEVIN SHEA on May 16, 2015ajs.sagepub.comDownloaded from
cruciate ligament (ACL) in predominantly young ath-
letes.
7,9,25,26,31,34
Studies that examine the efficacy of inter-
vention programs are time consuming, expensive, and
difficult to conduct. These limitations can lead to study
design and methodology flaws. These flaws subsequently
increase the risk for bias in the study and reduce the qual-
ity of evidence.
The purpose of this systematic review and meta-
analysis was to identify level 1 evidence studies of ACL
and knee injury prevention programs for soccer players,
assess the internal validity of these studies, and evaluate
the quantitative pooled effectiveness of these prevention
programs.
MATERIALS AND METHODS
Criteria for Selecting Studies
Types of Studies. Only evidence level 1 randomized con-
trolled trials (RCTs) of injury prevention programs as
defined by the Cochrane Handbook
24
were included. Level
of evidence assessments were made based on the criteria
described by the Oxford Centre for Evidence-Based Medi-
cine (http://www.cebm.net). Prospective, nonrandomized
studies (level 2), retrospective studies (level 3), case series
(level 4), and expert opinion (level 5) publications were not
included in the analysis. Non-English articles were
excluded from the study.
Types of Participants. Only studies with participants who
were limited to soccer players were included. Studies of
cohorts containing multiple different sport athletes were
excluded. Studies were not excluded because of any of the fol-
lowing factors: sex, skill level of athletes, or age group.
Types of Interventions and Comparison Groups. The
only studies included were those that used interventions
to prevent knee and/or ACL injuries. These interventions
included strengthening, stretching, proprioception, and
neuromuscular exercises. Studies were excluded if they
used an exogenous modality as used as a means of preven-
tion (eg, bracing, taping).
Outcome Measures. Studies were eligible for inclusion if
either ‘‘ACL’’ and/or ‘‘knee’’ injury was reported as an out-
come measure. We used the previously published defini-
tion of ‘‘knee injury’’ as any trauma, whether contact or
noncontact, whether acute or overuse, whether ligamen-
tous or nonligamentous, occurring to the knee. Acute inju-
ries were those with sudden onset with obvious trauma,
and overuse injuries were those occurring with an insidi-
ous onset.
18
Search Method and Strategy
The following major medical databases were searched from
inception through February 25, 2014: PubMed (Medline),
Embase, CINAHL, and Central (Cochrane Library). To
develop a sensitive and comprehensive search strategy,
a medical library search strategist (M.M.) was consulted,
who has participated in previous studies (see Acknowledg-
ments).
18
Briefly, the following search criteria were used:
((‘‘knee injuries’’[MeSH Terms] OR (‘‘knee’’[All
Fields] AND ‘‘injuries’’[All Fields]) OR ‘‘knee inju-
ries’’ [All Fields] OR (‘‘knee’’[All Fields] AND ‘‘injury’’
[All Fields]) OR ‘‘knee injury’’[All fields]) AND (‘‘pre-
vention and control’’[Subheading] OR (‘‘prevention’’
[All Fields] AND ‘‘control’’[All Fields]) OR ‘‘preven-
tion and control’’[All Fields] OR ‘‘prevention’’[All
Fields])) AND Clinical Trial[ptyp] and (ACL[All
Fields] AND (‘‘Inj Prev’’[Journal] OR (‘‘injury’’
[All Fields] AND ‘‘prevention’’[All Fields]) OR ‘‘injury
prevention’’[All Fields])) AND Clinical Trial[ptyp].
The search included supplemental bibliographic refer-
ence searches of articles to identify potentially missed,
relevant studies. For a more detailed list of the search
strategy used, see the Appendix (available online at
http://ajsm.sagepub.com/supplemental).
Data Collection and Analysis
Study Selection Procedure. Two reviewers (N.L.G. and
J.C.J.) independently conducted the article selection pro-
cess. The reviewers initially screened these articles on
the basis of title and abstract to determine whether the tri-
al met inclusion criteria. The full text was retrieved and
reviewed in detail if criteria were met. When disagree-
ments were noted, a third reviewer (K.G.S.) facilitated
group consensus agreement.
Data Extraction. Two reviewers (N.L.G. and J.C.J.)
independently extracted data from studies that met inclu-
sion criteria as described above. The following data were
extracted from each study: journal of publication, title,
author(s), publication year, subject sex, subject age, num-
ber of subjects in both intervention and treatment arm,
type of intervention(s), characteristics of intervention(s),
study design, follow-up time, and outcome data. Further-
more, the following outcome data elements were extracted
from each study: type of injury, frequency of injury occur-
rence, duration of follow-up, diagnostic methods for out-
comes of interest, number of dropouts, and compliance
rate. If any of the data elements of interest were missing
or unclear, the study authors were contacted for
clarification.
Risk-of-Bias Assessment. All randomized and cluster-
randomized controlled trials that met inclusion were
assessed for internal validity, and therefore risk of bias,
by 2 independent reviewers (N.L.G. and J.C.J.) using the
assessment algorithm described by van Tulder et al,
51
and
each was assigned a risk-of-bias score based on its assessed
internal validity (see Table 1). The van Tulder scale is one of
many critical appraisal tools used as an assessment for
RCTs developed and used by the Cochrane Spine Group.
51
This assessment focuses on several methodological criteria,
including randomization method, concealment of allocation,
blinding, and intention-to-treat analysis, that have been
shown to create an exaggeration of treatment effects and
lead to systematic bias.
35,39,41-44,54
These instruments are
recommended by PRISMA (Preferred Reporting Items for
Systematic Reviews and Meta-analyses)
29
and for reporting
systematic reviews in the orthopaedic literature.
55
2Grimm et al The American Journal of Sports Medicine
by KEVIN SHEA on May 16, 2015ajs.sagepub.comDownloaded from
If any of the specific criteria of the van Tulder scale
were not explicitly stated in a study’s manuscript, authors
were contacted for clarification. If disagreements arose,
a third reviewer was consulted (K.G.S.). This process of
assessment is consistent with the PRISMA statement for
conducting systematic reviews.
29
Meta-analysis and Statistical Procedures. All studies’
injury rates concerning intervention and control groups
were evaluated and summarized in tabular form for knee
and/or ACL injuries. Estimates of the intervention effect
on the incidence of knee and ACL injuries were expressed
as a relative risk (RR), which compared the knee/ACL inci-
dence rate in the intervention group (numerator) with the
rate in the comparison group (denominator).
The analysis of publication bias was performed with
Stata statistical software (Release 13; StataCorp LP) using
the Egger test, Harbord test, Peter test, and Begg test,
which are general approaches to test publication bias in
the meta-analysis. The Egger test has been widely used
and has become a standard procedure.
24,33
The first 3 tests
are the regression-based tests, which are parametric. How-
ever, the Begg test is based on a rank correlation method,
which is nonparametric. This was represented qualita-
tively using a funnel plot derivation.
With Stata, an inverse variance method was used to cal-
culate the weight for each study included using random-
effects meta-analyses with the DerSimonian-Laird method
to estimate the between-study variance.
10
The Cochrane Q
test, with a Pvalue of .10 being considered significant, and
the Higgins and the Thompson I
2
index were indepen-
dently used to assess heterogeneity among the studies.
23,24
These analyses were conducted separately for knee and
ACL injury. The estimated prospective statistical power
analysis was calculated to reach a power greater than 90%.
RESULTS
Search Findings
Using an a priori inclusion and exclusion criteria, our
search yielded 9 RCTs of knee/ACL injury prevention pro-
grams for soccer players from major medical literature
databases. We screened a total of 3377 articles based on
title and abstract, of which 79 full-text articles were
retrieved and reviewed in detail. This resulted in 9 RCTs
that met both inclusion and exclusion criteria (Figure 1).
Primary reasons for exclusion included nonrandomized
study design, no comparison group, and inclusion of sub-
jects who were non–soccer-playing athletes.
Study Characteristics
All studies and sample sizes included in this systematic
review and meta-analysis are provided in Table 2. A total
of 11,562 athletes were included in the 9 studies analyzed.
Five studies included only females,
17,47-49,52
3 studies
included only males,
12,14,50
and 1 study included both
males and females
13
(Table 2). All study designs were
either prospective cluster-randomized controlled trials or
prospective RCTs. Of the studies that met the inclusion
TABLE 1
Internal Validity Risk-of-Bias Assessment for Included Studies
Ekstrand
et al
12
(1983)
Soderman
et al
47
(2000)
Engebretsen
et al
14
(2008)
Gilchrist
et al
17
(2008)
Soligard
et al
48
(2008)
Steffen
et al
49
(2008)
Emery and
Meeuwisse
13
(2010)
van Beijsterveldt
et al
50
(2012)
Walden
et al
52
(2012)
(A) Was the method of randomization
adequate?
Yes
a
Yes
a
Yes
a
Yes
a
Yes
a
Yes Yes
a
Yes Yes
(B) Was the treatment allocation
concealed?
Yes
a
Yes
a
Yes
a
No Yes Yes
a
Yes
a
Yes Yes
(C) Were the groups similar at
baseline regarding the most
important prognostic indicators?
Yes Yes No Yes Yes Yes Yes Yes Yes
(D) Was the patient blinded to the
intervention?
No No No No No No No No No
(E) Was the care provider blinded to
the intervention?
No No No No No No No No No
(F) Was the outcome assessor blinded
to the intervention?
No No No No Yes Yes Yes No Yes
(G) Were the cointerventions avoided
or similar?
No Yes Yes Yes Yes Yes Yes Yes Yes
(H) Was the compliance acceptable in
all groups?
Yes
a
Yes No No
a
Yes No No Yes Yes
(I) Was the dropout rate described
and acceptable?
No
a
No No Yes Yes Yes Yes Yes Yes
(J) Was the timing of the outcome
assessment in all groups similar?
Yes Yes Yes Yes Yes Yes Yes Yes Yes
(K) Did the analysis include an
intention-to-treat analysis?
Yes
a
No Yes No Yes Yes Yes Yes Yes
Risk-of-Bias score 6 6 5 5 9 8 8 8 9
a
Ascertained via direct communication with primary or secondary author.
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criteria, 5 reported on knee injury alone and 4 reported
both knee and ACL injury (Table 3).
Risk of Bias
The average risk-of-bias score for the included studies was 7
of 11 (range, 5-9) (Table 1). Although all internal validity
elements of the van Tulder scale
51
were obtained from
each study, we contacted authors from 7 of the 9 included
studies to clarify at least 1 element that was not readily
available or clear in the manuscript. Two studies adequately
reported all elements of internal validity within their
respective manuscript.
50,52
Methodological elements that
were not performed included cointervention avoidance,
intention-to-treat analysis, care provider blinding, outcome
assessor blinding, and subject blinding. However, the latter
is logistically difficult with this particular study design.
Study-Specific and Quantitative Analysis
For overall knee injuries, the estimated RR was less than 1
(which is consistent with a protective effect) in 7 studies, of
which 2 were statistically significant individually (Figure
2A). The pooled effect size was statistically significant in
favor of injury prevention interventions showing a protec-
tive effect against overall knee injuries (RR, 0.74; 95% CI,
0.55-0.98; P= .039) (Figure 2A). For ACL injuries, the esti-
mated RR was less than 1 in 3 studies, which is consistent
with a protective effect. However, no study was statisti-
cally significant individually (Figure 2B). Likewise, the
pooled effect size showed a nonsignificant protective effect
against ACL injuries (RR, 0.66; 95% CI, 0.33-1.32; P= .238)
(Figure 2B). For sensitivity analyses, the data were ana-
lyzed with fixed-effects meta-analysis. In those analyses,
similar results in RR and CI were found.
Publication Bias
Using the methods for publication bias described above, for
studies that reported knee injuries, the estimated bias
coefficient from the Egger test is 20.97 with a standard
error of 1.14, giving a Pvalue of .422. Other tests also
showed no small-study effects (P= .537 [Harbord test],
.463 [Peter test], and .532 [Begg test]). The test thus pro-
vides no evidence of publication bias and can be seen qual-
itatively in the funnel plot (Figure 3A). Similarly, for
studies that reported ACL injuries, the estimated bias coef-
ficient is 3.17 with a standard error of 0.89, giving a P
value of .071 with the Egger test and thus no evidence of
publication bias. Other tests provided similar results
except the result based on the Peter test (P= .131 [Harbord
test], .022 [Peter test], and .174 [Begg test]). This can be
seen qualitatively in the funnel plot (Figure 3B).
DISCUSSION
For this systematic review and meta-analysis, we found 9
high-quality RCTs designed to prevent knee and/or ACL
injuries in athletic soccer players. The quantitative pooled
effect suggests a significant protective effect against over-
all knee injuries in this population (RR, 0.74; 95% CI,
0.55-0.98; P= .039); however, a nonsignificant protective
effect for ACL injuries was found (RR, 0.66; 95% CI,
0.33-1.32; P= .238). Given the relatively small number of
studies meeting inclusion for our meta-analysis, we did not
perform subgroup analyses based on sex, skill level, or spe-
cific intervention type. It has been shown that multiplicity
of analysis increases the risk of type 1 error, resulting in spu-
rious results, and should be performed and interpreted with
caution.
28,45
Our study was designed a priori to have the sta-
tistical power to detect a difference in knee and ACL effects
using a random-effects model, and therefore the modifying
effects of individual covariates would not have sufficient
power for detection. Therefore, we cannot say which elements
of the intervention were more or less effective. Neither are we
able to clearly comment on the effects of the interventions rel-
ative to gender.
Outside of the studies analyzed in this meta-analysis
and systematic review, several injury prevention studies
have been published regarding handball,
31,32,53
soc-
cer,
9,20,22,34
basketball,
22,34
volleyball,
22,34
football,
7
and
skiing.
15
However, given the logistical, methodological,
and financial complexity of conducting an injury preven-
tion study in athletes, relatively few have been conducted
at the highest methodological rigor—the RCT. To date,
all of the published systematic reviews and meta-analyses
on injury prevention programs have included both random-
ized and nonrandomized studies.
16,19,21,56
The data of these
meta-analyses should therefore be evaluated with caution
given the mixing of several study designs, cohorts, and
individual knee/ACL injury risks.
For example, the recent meta-analysis by Gagnier et al
16
on ACL injury prevention programs showed a statistically
significant reduction of ACL injuries through the use of
injury prevention programs. However, the difference in
Figure 1. PRISMA flow diagram for study selection.
4Grimm et al The American Journal of Sports Medicine
by KEVIN SHEA on May 16, 2015ajs.sagepub.comDownloaded from
TABLE 2
Summary Table of Study Characteristics
a
Study Journal
Publication
Year LOE
Subjects’
Sex
Age, y,
Mean (Range)
Program
Exercises
Study
Design
Follow-
up
No. of
Subjects
at Follow-up
Ekstrand
et al
12
American Journal
of Sports
Medicine
1983 1 Male 24.0 (17-37) Multifaceted approach:
protective gear, taping,
and warm-up and
flexibility program
b
Prospective, cluster-
randomized
controlled study
6 mo 180
Soderman
et al
47
Knee Surgery,
Sports
Traumatology,
Arthroscopy
2000 1 Female 20.4 (NR) Proprioceptive (balance
board)
Prospective, cluster-
randomized
controlled study
6 mo 140
Engebretsen
et al
14
American Journal
of Sports
Medicine
2008 1 Male NR Balance training Prospective
randomized
controlled study
8 mo 131
Gilchrist
et al
17
American Journal
of Sports
Medicine
2008 1 Female 19.9 (NR) Multifaceted approach:
warm-up, stretching,
strength, plyometrics,
and agility training
Prospective, cluster-
randomized
controlled study
3 mo 1435
Soligard
et al
48
British Medical
Journal
2008 1 Female 15.4 (13-17) Multifaceted approach:
warm-up, stretching,
plyometrics, and
balance training
Prospective, cluster-
randomized
controlled study
8 mo 1892
Steffen
et al
49
Scandinavian
Journal of
Medicine and
Science in
Sports
2008 1 Female 15.4 (13-17) Multifaceted approach:
core stabilization,
balance, plyometrics,
and strength training
Prospective, cluster-
randomized
controlled study
6 mo 2020
Emery
and
Meeuwisse
13
British Journal of
Sports Medicine
2010 1 Male and
female
NR
(12-18)
Dynamic stretching,
eccentric strength,
agility, jumping,
balance
Prospective, cluster-
randomized
controlled study
12 mo 744
van
Beijsterveldt
et al
50
British Journal of
Sports Medicine
2012 1 Male 24.8 (20-29) Core stability,
proprioception,
dynamic stabilization,
plyometrics, eccentric
muscle training
Prospective, cluster-
randomized
controlled study
1 season 456
Walden
et al
52
British Medical
Journal
2012 1 Female 14 (12-17) Neuromuscular
exercises, jump-
landing technique
Prospective, cluster-
randomized
controlled study
1 season 4564
a
LOE, level of evidence; NR, not reported (data not reported and unable to contact primary or secondary author).
b
The use of protective gear and taping only applied to the shin and ankle. No exogenous interventions were applied to the knee.
TABLE 3
Injury Data for Included Studies
a
Knee Injuries, % (n/N) ACL Injuries, % (n/N)
Study Prevention Control PValue Prevention Control PValue
Ekstrand et al
12
1.1 (1/90) 18.9 (17/90) \.05 NR NR NR
Soderman et al
47
12.9 (8/62) 7.7 (6/78) NR 6.5 (4/62) 1.3 (1/78) NR
Engebretsen
et al
14
10.8 (7/65) 12.1 (8/66) .93 NR NR NR
Gilchrist et al
17
6.9 (40/583) 6.8 (58/852) .86 1.2 (7/583) 2.1 (18/852) .2
Soligard et al
48
3.1 (33/1055) 5.6 (47/837) .08 NR NR NR
Steffen et al
49
3.4 (37/1073) 3.2 (30/947) ..05 0.4 (4/1073) 0.5 (5/947) .73
Emery and
Meeuwisse
13
0.8 (3/380) 2.2 (8/364) .232 NR NR NR
van Beijsterveldt
et al
50
10.8 (24/223) 17.2 (40/233) NR NR NR NR
Walden et al
52
1.9 (48/2479) 2.1 (44/2085) .71 0.3 (7/2479) 0.7 (14/2085) .02
a
ACL, anterior cruciate ligament; LOE, level of evidence; NR, not reported (data not reported and unable to contact primary or secondary author).
Vol. XX, No. X, XXXX Soccer Injury Prevention: Meta-analysis 5
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findings may be explained by noting that Gagnier et al
16
included several different athletic populations in their anal-
ysis (eg, soccer, handball, basketball, volleyball) and they
included both evidence level 1 randomized studies and lev-
els 2 and 3 nonrandomized studies. It is well published
that these individual sports have variable ACL and knee
injury risks.
46
Additionally, it is well understood that non-
randomized trials can lead to an exaggeration of treatment
effects and greater chance of an introduction of bias into
astudy.
27,54
This exaggeration of treatment effects is
perhaps suggested by the subgroup analysis by Gagnier
et al
16
showing that the pooled effect of the randomized
studies was not statistically significant; however, non-
randomized studies demonstrated significant benefit.
In our study we attempted to control for this shortcom-
ing by including only level 1 studies as they pertained to
a single sport (soccer) and limiting the multiplicity of anal-
yses. Although we adhered to a strict protocol, following
the PRISMA guidelines,
29
for collection, interpretation,
and analysis, our study is not without limitations. First,
Figure 2. (A) Random-effects model with DerSimonian-Laird weighting method showing a statistically significant risk ratio in favor
of injury prevention programs for reducing knee injuries. (B) Random-effects model with DerSimonian-Laird weighting method
showing no statistically significant benefit for ACL injury prevention.
Figure 3. (A) Funnel plot with 95% confidence interval showing no evidence of publication bias for injury prevention programs
evaluating knee injury prevention. (B) Funnel plot with 95% confidence interval showing no evidence of publication bias for injury
prevention programs evaluating anterior cruciate ligament injury prevention.
6Grimm et al The American Journal of Sports Medicine
by KEVIN SHEA on May 16, 2015ajs.sagepub.comDownloaded from
we did not blind the reviewers (N.L.G. and J.C.J.) to study
author, institution, or journal in which the study was pub-
lished. Although the extra step of blinding the reviewed
manuscripts has been performed in other reviews, it is
an onerous extra step with little evidence to support its
ability to protect against bias.
6
Furthermore, with a small
number of studies (n \10), the assessment of publication
bias should be interpreted with caution.
24
Although there
are no strict guidelines on the absolute number of studies
needed to detect a true publication bias, the larger the
sample the more accurate the assessment of bias will be.
Nonetheless, we used recommended analytical techniques
for detection of publication bias.
24,33,38
Additionally, one
of the authors (K.G.S.) has published on knee injury pre-
vention programs in a cohort of female soccer, basketball,
and volleyball players.
34
This study showed no treatment
benefit, and an argument could be made that this could
introduce selection bias. However, we attempted to control
for this by removing this author as a reviewer of selected
studies and involving this author only when consensus
was needed for disagreement between the primary
reviewers (N.L.G. and J.C.J.).
CONCLUSION
To our knowledge, we have conducted the first level 1
meta-analysis of injury prevention programs in soccer ath-
letes. While this analysis supports the use of injury preven-
tion programs for preventing overall knee injuries in this
athletic population, a nonsignificant reduction in ACL
injuries was observed through meta-analytical techniques.
Similar to the authors of previous studies,
16
we cannot say
with much confidence what components of the injury pre-
vention programs are most effective; however, neuromus-
cular training has showed promising results.
30
Given the logistical challenges of conducting high-
quality RCTs on injury prevention in this population, we
applaud the researchers who have performed these
much-needed scientific studies and urge future investiga-
tors to follow the standards set forth by the CONSORT
(Consolidated Standards of Reporting Trials) statement
40
for reporting this research in our athletic population.
ACKNOWLEDGMENT
The authors thank Mary McFarland of the Eccles Health
Science Medical Library for assisting with the develop-
ment of a sensitive search strategy for this study.
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... injuries per team per season in football professional teams [17,20]. As a result of the low number of ACL injuries suffered per season, some potentially effective interventions could not be able to reach significance when rate is used to evaluate their efficacy [21,22]. As an alternative, in the purpose of reducing ACL injuries, intervention programs could be also developed with the aim of modifying risk factors of ACL injury [23], and efficacy could be assessed by measuring changes in proxy factors (i.e., surrogates of injury) [24,25]. ...
... To date, several systematic reviews have been published in the field of ACL injury prevention in athletes [21,23,[37][38][39][40][41]. The last research in football players is the work published by Grimm and collaborators [21], where only randomized-controlled trials (RCT) in which ACL injury incidence was reported were included. ...
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Systematic reviews should build on a protocol that describes the rationale, hypothesis, and planned methods of the review; few reviews report whether a protocol exists. Detailed, well-described protocols can facilitate the understanding and appraisal of the review methods, as well as the detection of modifications to methods and selective reporting in completed reviews. We describe the development of a reporting guideline, the Preferred Reporting Items for Systematic reviews and Meta-Analyses for Protocols 2015 (PRISMA-P 2015). PRISMA-P consists of a 17-item checklist intended to facilitate the preparation and reporting of a robust protocol for the systematic review. Funders and those commissioning reviews might consider mandating the use of the checklist to facilitate the submission of relevant protocol information in funding applications. Similarly, peer reviewers and editors can use the guidance to gauge the completeness and transparency of a systematic review protocol submitted for publication in a journal or other medium.
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Objective. —To determine if inadequate approaches to randomized controlled trial design and execution are associated with evidence of bias in estimating treatment effects. Design. —An observational study in which we assessed the methodological quality of 250 controlled trials from 33 meta-analyses and then analyzed, using multiple logistic regression models, the associations between those assessments and estimated treatment effects. Data Sources. —Meta-analyses from the Cochrane Pregnancy and Childbirth Database. Main Outcome Measures. —The associations between estimates of treatment effects and inadequate allocation concealment, exclusions after randomization, and lack of double-blinding. Results. —Compared with trials in which authors reported adequately concealed treatment allocation, trials in which concealment was either inadequate or unclear (did not report or incompletely reported a concealment approach) yielded larger estimates of treatment effects ( P P =.01), with odds ratios being exaggerated by 17%. Conclusions. —This study provides empirical evidence that inadequate methodological approaches in controlled trials, particularly those representing poor allocation concealment, are associated with bias. Readers of trial reports should be wary of these pitfalls, and investigators must improve their design, execution, and reporting of trials. ( JAMA . 1995;273:408-412)