Background: Prospective studies have reported that abnormal movement patterns at the trunk, hip, and knee are associated with non-contact ACL injuries. Impaired hip strength may underlie these abnormal movement patterns, suggesting that diminished hip strength may increase the risk of non-contact ACL injury. Purpose: To determine if baseline hip strength predicts future non-contact ACL injury in athletes. Study Design: Prospective cohort study. Methods: Prior to the start of the competitive season, isometric hip strength (external rotator and abductor) was measured bilaterally using a hand-held dynamometer in 501 competitive athletes (138 females and 363 males) participating in various sports. During the sport seasons, ACL injury status was recorded, and injured athletes were further classified based on the mechanism of injury (non-contact vs. contact). Postseason, logistic regression was used to determine whether baseline hip strength predicted future non-contact ACL injury. Receiver operating characteristic (ROC) curves were constructed independently for each strength measure to determine the clinical cut-off value to distinguish between a high-risk and low-risk outcome. Results: A total of 15 non-contact ACL injuries were confirmed (6 female, 9 male), for an overall annual incidence of 3.0% (2.5% for males and 4.3% for females). Baseline hip strength measures (external rotator and abductor) were significantly lower in injured athletes compared to non-injured athletes (p = 0.003 and p < 0.001, respectively). Separate logistic regression models indicated impaired hip strength increased future injury risk [external rotator: OR = 1.23 (95% CI: 1.08, 1.39), p = 0.001; abductor: OR = 1.12 (95% CI: 1.05, 1.20), p = 0.001]. Clinical cutoffs to define high risk were established as external rotator strength ≤ 20.3% body weight (BW) or abductor strength ≤ 35.4% BW. Conclusion: Measures of preseason isometric hip abductor and external rotator strength independently predicted future non-contact ACL injury status in competitive athletes. Our data suggest that screening procedures to assess ACL injury risk should include an assessment of isometric hip abductor and/or external rotator strength.

1. Hip
Muscle
Strength
Predicts
Non-­‐contact
ACL
Injury
in
Male
and
Female
Athletes:
A
Prospec@ve
Study
Rachel
K.
Straub,
MS,
CSCS*
Khalil
Khayambashi,
PT,
PhD**
Navid
Ghoddosi,
MS**
Christopher
M.
Powers,
PT,
PhD,
FACSM,
FAPTA*
University
of
Isfahan;
Isfahan,
Iran.**
University
of
Southern
California;
Los
Angeles,
CA.*
ACL
Research
Retreat:
March
19-­‐21,
2015

2. Introduc=on
Methods
Results
Discussion
Conclusion
Prospec@ve
Studies
• Abnormal
movement
paEerns
at
trunk,
hip,
and
knee
have
been
shown
to
be
independent
risk
factors
for
non-­‐contact
ACL
injuries
in
athletes
(HeweE
et
al.,
2005;
Paterno
et
al.,
2010;
Zazulak
et
al.,
2007).
Cross-­‐sec@onal
Studies
• Impaired
hip
strength
may
underlie
these
abnormal
movement
paEerns
(Claiborne
et
al.,
2006;
Hollman
et
al.,
2009;
Jacobs
et
al.,
2007;
Lawrence
et
al.,
2008;
Lee
S-­‐P
and
Powers,
2013;
Willson
et
al.,
2006).
2

3. Introduc=on
Methods
Results
Discussion
Conclusion
So
the
ques@on
is.
.
.
Can
hip
strength
predict
non-­‐contact
ACL
injury?
Why
is
this
relevant?
If
hip
strength
can
be
shown
to
predict
non-­‐contact
ACL
tears,
this
may
be
an
easier
way
to
screen
athletes
at
risk
for
injury
(as
opposed
to
more
complicated
kinema=c
analyses).
3

4. Introduc=on
Methods
Results
Discussion
Conclusion
Primary
Aim
• To
determine
whether
baseline
hip
strength
can
predict
future
non-­‐contact
ACL
injury
in
compe==ve
athletes
Secondary
Aim
• To
establish
clinical
cutoffs
for
baseline
hip
strength
that
predict
future
injury
with
high
specificity
&
sensi=vity
4

5. Introduc=on
Methods
Results
Discussion
Conclusion
Subjects
• 501
compe==ve
athletes
– 138
females
and
363
males
par=cipa=ng
in
various
sports
(futsal,
soccer,
volleyball,
handball,
basketball)
• No
previous
ACL
injury
or
previous
LE
injury
during
the
past
6
months
5

6. Assessment
(Preseason)
• 10
raters
trained
to
assess
isometric
hip
strength
(external
rota=on
&
abduc=on)
using
a
hand-­‐held
dynamometer
• Intra-­‐rater
reliability
– Hip
ER:
0.81
to
0.98
– Hip
ABD:
0.95
to
0.99
• Inter-­‐rater
reliability
– Hip
ER:
0.99
– Hip
ABD:
0.71
Introduc=on
Methods
Results
Discussion
Conclusion
6

7. Introduc=on
Methods
Results
Discussion
Conclusion
Assessment
(During
Sports
Season)
• ACL
injury
status
recorded.
– Non-­‐injured
– Injured
• Contact
• Non-­‐contact
7

8. Introduc=on
Methods
Results
Discussion
Conclusion
Data
Analysis
(Postseason)
• Preliminary
analysis
used
to
determine
poten=al
predictors
of
non-­‐contact
ACL
injury.
– Two-­‐way
ANOVAs
(injury
x
sex)
for
con=nuous
variables
(age,
ht,
wt,
hip
ER
strength,
hip
ABD
strength)
– Fisher’s
exact
tests
for
categorical
variables
(sport,
gender)
• Variables
that
were
significantly
different
between
injured
and
non-­‐injured
groups
were
considered
as
predictors
in
logis=c
models
(p
<
0.05).
• ROC
curves
constructed
for
each
hip
strength
measure
to
determine
clinical
cut-­‐off
values.
8

9. 30
Males
Excluded
• 5
ACL
Contact
Injuries
• 25
Inconclusive
Diagnoses
3
Females
Excluded
• 3
ACL
Contact
Injuries
501
Subjects
363
Males
138
Females
333
Males
Final
Sample
135
Females
Final
Sample
468
Total
Athletes
Introduc=on
Methods
Results
Discussion
Conclusion

10. Introduc=on
Methods
Results
Discussion
Conclusion
Annual
Non-­‐contact
ACL
Injury
Rate
• Overall
injury
rate
3.0%
(15
of
501)
– Males:
2.5%
(9
of
363)
– Females:
4.3%
(6
of
138)
hEp://sportskneetherapy.com/tag/acl-­‐recovery/
10

11. Introduc=on
Methods
Results
Discussion
Conclusion
Injuries
by
Sport
&
Gender
11
Sport
Futsal
Soccer
Volleyball
Basketball
Handball
Male
(n
=
333)
Injured
(n
=
9)
Non-­‐injured
(n
=
324)
3
(6.5%)
43
(93.5%)
3
(1.6%)
179
(98.4%)
1
(2.6%)
37
(97.4%)
0
24
(100%)
2
(4.7%)
41
(95.3%)
Female
(n
=
135)
Injured
(n
=
6)
Non-­‐injured
(n
=
129)
2
(7.7%)
24
(92.3%)
0
0
0
33
(100%)
4
(7.1%)
52
(92.9%)
0
20
(100%)

12. Introduc=on
Methods
Results
Discussion
Conclusion
Baseline
Variables
• Two-­‐way
ANOVAs
for
con=nuous
variables
– All
interac=ons
non-­‐significant
(p
>
0.05).
– All
injury
main
effects
non-­‐significant
(p
>
0.05)
except
for
hip
ADB
and
ER
strength
• Fisher’s
exact
test
for
categorical
– Neither
sex
nor
sport
associated
with
injury
status
(p
>
0.05).
12

13. 22.1
37.8
17.2
30.8
0
5
10
15
20
25
30
35
40
45
50
%BW
ER ABD
Non-injured
Injured
Introduc=on
Methods
Results
Discussion
Conclusion
13
Hip
Strength:
Non-­‐injured
vs.
Injured
p
=
0.003
p
<
0.001

14. Introduc=on
Methods
Results
Discussion
Conclusion
Logis@c
Models
• Strength
measures
highly
correlated
– (r
=
0.66,
p
<
0.01)
• Model
1:
– ER:
OR
=
1.23
(95%
CI:
1.08,
1.38),
p
=
0.001,
R2
=
11.2%
• Model
2:
– ABD:
OR
=
1.12
(95%
CI:
1.05,
1.20),
p
=
0.001,
R2
=
10.2%
14

15. Introduc=on
Methods
Results
Discussion
Conclusion
ROC
Curves
• High
Risk
Cutoffs
– ER:
≤
20.3
%BW
• Sensi@vity
=
89%
• Specificity
=
59%
– ABD:
≤
35.4
%BW
• Sensi@vity
=
87%
• Specificity
=
65%
15

16. Probability
of
Future
Injury
Based
on
Preseason
Hip
Strength
Test
• High
Risk
– ER:
3.0%
à
6.6%
– ABD:
3.0%
à
7.2%
• Low
Risk
– ER:
3.0%
à
0.34%
– ABD:
3.0%
à
0.65%
16
Introduc=on
Methods
Results
Discussion
Conclusion

17. ER
(%BW)
Leetun
Current
17.9
17.2
20.6
22.1
Introduc=on
Methods
Results
Discussion
Conclusion
• Female
vs.
male
injury
rate:
4.3%
vs.
2.5%
– Our
results
indicated
sex
did
not
impact
injury
status.
• Logis@c
models
as
a
whole
explained
only
10-­‐11%
of
the
varia@on
in
injury
status.
• How
do
our
strength
values
compare?
– Leetun
et
al.,
2004
17
ABD
(%BW)
Leetun
Current
28.6
30.8
31.6
37.8
Injured
ê
Non-­‐Injured
é

18. • Preseason
isometric
hip
strength
(abduc@on
and
external
rota@on)
independently
predict
future
non-­‐contact
ACL
injury
in
compe@@ve
athletes.
• Screening
procedures
to
assess
ACL
injury
risk
should
consider
assessment
of
isometric
hip
abduc@on
and/or
hip
external
rota@on
strength.
Introduc=on
Methods
Results
Discussion
Conclusion
18

19. References
1. Claiborne
TL,
Armstrong
CW,
Gandhi
V,
Pincivero
DM.
Rela=onship
between
hip
and
knee
strength
and
knee
valgus
during
a
single
leg
squat.
J
Appl
Biomech.
2006;22(1):41-­‐50.
2. HeweE
TE,
Myer
GD,
Ford
KR,
et
al.
Biomechanical
measures
of
neuromuscular
control
and
valgus
loading
of
the
knee
predict
anterior
cruciate
ligament
injury
risk
in
female
athletes:
a
prospec=ve
study.
Am
J
Sports
Med.
2005;33(4):492-­‐501.
3. Hollman
JH,
Ginos
BE,
Kozuchowski
J,
Vaughn
AS,
Krause
DA,
Youdas
JW.
Rela=onships
between
knee
valgus,
hip-­‐
muscle
strength,
and
hip-­‐muscle
recruitment
during
a
single-­‐limb
step-­‐down.
J
Sport
Rehabil.
2009;18(1):104-­‐117.
4. Jacobs
CA,
Uhl
TL,
MaEacola
CG,
Shapiro
R,
Rayens
WS.
Hip
abductor
func=on
and
lower
extremity
landing
kinema=cs:
sex
differences.
J
Athl
Train.
2007;42(1):76-­‐83.
5. Lawrence
RK,
3rd,
Kernozek
TW,
Miller
EJ,
Torry
MR,
Reuteman
P.
Influences
of
hip
external
rota=on
strength
on
knee
mechanics
during
single-­‐leg
drop
landings
in
females.
Clin
Biomech
(Bristol,
Avon).
2008;23(6):806-­‐813.
6. Lee
S-­‐P,
Powers
CM.
Individuals
with
Diminished
Hip
Abductor
Muscle
Strength
Exhibit
Altered
Ankle
Biomechanics
&
Neuromuscular
Ac=va=on
during
Unipedal
Balance
Tasks.
Gait
&
Posture.
2013.
7. Leetun
DT,
Ireland
ML,
Willson
JD,
Ballantyne
BT,
Davis
IM.
Core
Stability
Measures
as
Risk
Factors
for
Lower
Extremity
Injury
in
Athletes.
Medicine
&
Science
in
Sports
&
Exercise.
2004;36(6):926-­‐934.
8. Paterno
MV,
SchmiE
LC,
Ford
KR,
et
al.
Biomechanical
measures
during
landing
and
postural
stability
predict
second
anterior
cruciate
ligament
injury
auer
anterior
cruciate
ligament
reconstruc=on
and
return
to
sport.
Am
J
Sports
Med.
2010;38(10):1968-­‐1978.
9. Willson
JD,
Ireland
ML,
Davis
I.
Core
strength
and
lower
extremity
alignment
during
single
leg
squats.
Med
Sci
Sports
Exerc.
2006;38(5):945-­‐952.
10. Zazulak
BT,
HeweE
TE,
Reeves
NP,
Goldberg
B,
Cholewicki
J.
Deficits
in
neuromuscular
control
of
the
trunk
predict
knee
injury
risk:
a
prospec=ve
biomechanical-­‐epidemiologic
study.
Am
J
Sports
Med.
2007;35(7):1123-­‐1130.
19

20. For
Further
Informa=on.
.
.
20
Paper
accepted
at
American
Journal
of
Sports
Medicine
September
1,
2015.
Full
Paper
Coming
Soon!