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6/12/2013
1
Edward M. Wojtys, M.D.
University of Michigan
ACL Prevention
Programs
Conflicts of InterestNone
DisclosuresNIH/NIAMS—R01 AR054821
Coulter Foundation Grant
KIA Research—Consultant
Center for Organogenesis
NFL—Injury and Safety Panel
Sports Health—Editor
Damaging Forces
⇓
Failed
Dynamic Protection
⇓⇓⇓⇓
ACL Tears
ACL Injury Cascade
Mechanisms of Injury
?
Remains Unopened…
ACL Injury
Prevention
secrets
??
?
?
??
The Big Black Box
Scandanavian
registry:
•Median age ~25
•Range= 5-70 years
Granan Acta Orthop 2009
Danish registry
Lind Acta Orthop 2009
Adolescent females
Age Distribution
6/12/2013
2
Risk Factors for
Contralateral ACL
(Systematic Review – 13 Prospective)
Contralateral 1st Time
Risk Risk
Sward KSST 2010
# 1 Risk Factor for
Contralateral ACL Injury
Return to High
Level Activity
Sward KSST 2010
ACL Injury Prevention Programs
• Kinetics
• Kinematics
• Education
• Compliance
Females have 100% longer rise times in isometric force development.
Komi Acta Physiol Scand 1978
• 52 NCAA athletes– High risk sports of basketball, volleyball,
soccer
(12 male, 12 female)
– Low risk sports of cycling, rowing, running
(14 male, 14 female)
• Body-matched male/female pairs for age and sport
• Strength testing (Biodex)
• Rotational knee stiffness device
Gender Differences in Rotational
Knee Stiffness
Wojtys JBJS 2003
• Females increased volitional knee stiffness significantly less than males (p<0.05).
• Female athletes in pivot sports had lowest volitional increase in knee joint stiffness.
Female (pivot sport) 171%
Female (non-pivot sport) 198%
Male (non-pivot sport) 207%
Male (pivot sport) 258%
Gender Differences in Rotational
Knee Stiffness
Wojtys JBJS 2003
6/12/2013
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Coordinated,
efficient muscle effort.
Engrams
Kottke Arch Phys Med 1980
ACL Injury Prevention
in Alpine Skiing
• Injury Mechanism Education
(Avoiding hazardous positions)
• Prospective
• 62% Reduction in ACL Injuries
Ettlinger AJSM 1995
ACL Prevention
Kinematics, Kinetics, Education
Neuromuscular Prevention
(Youth Soccer)
• Knee, ankle, lower extremity
• 60 teams - 32 trained
28 control
• Males & females
• Cluster randomized trial
• Stretches, eccentrics, agility,
jumping, & balance
Emery BJSM 2010
Injury Rate
Per 1,000 player hours
Trained – 2.08 injuries
Control 3.35
Neuromuscular Training is
Protective!
Emery BJSM 2010
Adolescent & Female
Football
• Stratified cluster randomized trial
• 230 Swedish clubs(121 – intervention)
• 4.564 players (12-17 y.o.)
• 15 min warm-up 2x week(core, balance, allignment)
Walden BMJ 2012
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ACL Injuries
Intervention – 7 (0.28%)
Control – 14 (0.67%)
Reduction in ACL – Injury rate
64%
Walden BMJ 2012
Knee Injuries - Soccer
• 1,506 females (13-19 y.o.)
• Community based intervention
• Motor skills, body control, & muscle
activation & education
Kiani Arch Int. Med. 2010
Intervention – 3 injuries
Incidence – 0.04/1000 player hrs
Control – 13 injuries
0.20/1000 player hrs
77% reduction knee injuries
90% reduction noncontact
Kiani Arch Int. Med. 2010
Prevention of Knee Injuries
• Systematic review (1966-2001)
• 328 studies identified � 14 included
• 5 brace studies � Negative
• 3 shoe cleats / ski boot-binding � ?
• 6 prospective, neuromuscular � Positive
Thacker J Sports Med Phys Fit 2003
Knee Ligament Injury Prevention
(KLIP)
• 577 female athletes
(soccer, b-ball, v-ball)
862 controls
• 20 min / session – 2x / week
• Non randomized – coach resistance
No Reduction in ACL Injuries!
Pfeiffer JBJS 2006
Injury Prevention - Soccer
• Randomized trial – high and low risk
Intervention and control
• Ankle, knee, hamstrings, groin
• Training compliance (HR)
27.5% Ankle
29.2% Knee
21.1% Hamstrings
19.4% Groin
Engebretsen AJSM 2008
6/12/2013
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Effectiveness of ACL
Injury Prevention
• Meta-analysis of prospective
controlled studies
• 909 studies identified
9 included
Sadoghi JBJS 2012
Caraffa 1996
Gilchrist 2008
Heidt 2000
Hewett 1999
Mandelbaum 2005
Petersen 2002
Petersen 2005
Pfeiffer 2006
Sadoghi JBJS 2012
Sadoghi Studies
• Scientific quality – low
• Issues – blinding, randomization,
few matched pairs, drop-out rates
• Only 1 study with power analysis
• Study outcome heterogeneity
• 5/9 – soccer
• Low numbers
Sadoghi JBJS 2012
Pooled Risk Ratio
Females 0.48 95% C.I. = 0.26-0.89
Males 0.15 95% C.I. = 0.08-0.28
ACL injury risk reduction significant
for females 52% (p=0.021) and
males 85% (p<0.001)
Sadoghi JBJS 2012
Meta-Regression
Balance Board � no effect (p=0.712)
Video assistance � no effect (0.914)
F/U duration � no effect (0.437)
Year of publication � no effect (0.358)
On the pooled risk
Sadoghi JBJS 2012
? Best Program ?
• Study heterogeneity
• At least 10 min – 3 x / week
Neuromuscular
Sadoghi JBJS 2012
6/12/2013
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Meta-Regression (Training)
Preseason vs. playing season reduced risk by 19.1% (p=0.691)
Sadoghi JBJS 2012
ACL Injury Prevention and
Performance Enhancement
• Systematic Review (1995-2011)
• 57 Studies – 42 Programs
Sportsmetrics
Myklebust
17 Studies KLIP
PEP
11 (HOLM)
Noyes Sports Health 2012
ACL Injury Incidence Reduction
(AE*)
PEP and Sportsmetrics
*Athletic Performance Improvements
Noyes Sports Health 2012
Clinical Incidence Rate
Injuries
Athletes
At Risk (N)
ACL Injury Rate
Injuries
Athletic
Exposures (AE)
Sportsmetrics
ACL Injury
Reduction
• Very successful
Improved Athletic
Performance
• 60-120 min / 3x week
• Pre-Season
Noyes Sports Health 2012
6/12/2013
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PEP
• Very Good
In-Season – 20 min before practice
? Athletic Performance ?
Noyes Sports Health 2012
ACL Injury
Reduction
Prevention Programs
• Landing technique
• Cutting maneuvers
• Deceleration
Tailored to the Athlete
Sports Specific
Artificial Turf vs Grass
• Prospective Cohort –
2020 players (109 teams)
• Young female football players (2005)
Risk of Acute Ankle/Knee Injury was
Similar!
Steffen BJSM 2007
Field Turf vs. Grass
(NFL)
• Descriptive Retrospective Study
• 2000-2009 (5360 team/games)
Injury Rate 67% on Field Turf
Hershman AJSM 2012
Compliance
Athletic Injury
Performance Prevention
Balance
Summary
• Injury prevention hampered by lack
of ACL injury mechanism
understanding
• Still not sure what Sportsmetrics,
PEP, and other successful
programs change?
6/12/2013
8
Thank You
ACL Injury Prevention
(Meta-Analysis)
Plyometric Balance
Strength Training Training
*Most effective – females (<18 yo) soccer
Yoo KSST 2010
Warm-up Program
(cluster randomized trial)
• 1892 female footballers (13-17 y.o.)
• Foot, ankle, leg, knee, thigh, groin, & hip
• Strength, awareness, & NM control
Risk of all injuries, severe & overuse, was reduced!
(Lower extremity injury rate did not change)
Soligard BMJ 2008
ACL-R Risk Factors
Activity Level & Graft Type
• Case-control 21 pts – 42 matched
• Univariate logistic regression
Low vs. high activity – OR 5.53
(95% C.I. 1.18-28.61)
Allo vs. auto – OR 5.56
(95% C.I. 1.55-19.98)
Borchers AJSM 2009
Goals
Enhanced condition
Prevent muscle fatigue
Hamstring fatigue � Transverse plane
Control Deficits
Nyland JAT 1999
Hamstring Training
Eccentric > Concentric
(Improving quad/hamstring)
(* Professional soccer players)
Mjolsnes SJ Med Sci Sports 2004
6/12/2013
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Gluteal Training(Abductors, Extensors, External Rot.)
• Plyometric training
Dynamic L.E. control & positioning at
ground contact
Chimera JAT 2004
Core
• Pertebation training
• Body sway control
Jamison MSSE 2012
Hamstring Strength
• Concentric vs. eccentric
• 21 well trained male soccer players
• 2x6 reps �3x(8-12) reps x2/weeks
load x 6 weeks
11% in eccentric torque (60)
No ∆ in concentric
Mjolsnes Scand JMS Sports 2004
Knee Injuries – Alpine Skiing
• Education program (1993-94)
20 intervention
22 control
• 179 serious injuries
• 62% reduction with education
Ettlinger AJSM 1995
Ski areas
Contra vs. Ipsilateral ACL Injury
• 63 ACL-R
• 39 controls
• 12 month f/u
• 16 ACL-R, 1 control � ACL
* Female ACL-R
16x injury rate (controls)
4x ACL
Paterno Clin J. Sport Med 2012
4x male risk – 2nd ACL
6x male risk – contra ACL
Paterno Clin J. Sport Med 2012
Female Athletes
6/12/2013
10
ACL Retear and
Contralateral Injury Risk
• Prospective cohort (Level II)
• 2y data – 235(273) 86%
• 7 retears (3%) 7 contra (3%)
Moon AJSM 2007
Ekstrand 75%
Vermont 62%
Cincinnati (Sportsmetrics) 72%
Wedderkopp 71-80%
Caraffa 87%
Santa Monica (PEP) 88%, 74%
Soderman 0%
Decrease in ACL tears
ACL Prevention Success Rates
Dissipate damaging forces
Education
Avoid hazards
(proper form, positioning, anticipation)
Neuromuscular Protection
Injury Situation
• 20 min warm-up (video)– 2-3 times/week for 12 weeks
• Avoidance techniques
• Stretch and strengthen
• Plyometrics
• Soccer agilities
PEP Program
Mandelbaum AOSSM 2002
1041 soccer trainees – 0.2 injuries/player
1902 soccer controls – 1.7 injuries/player
2002 88% ↓ in ACL Injuries
2003 74% ↓ in ACL Injuriesa
PEP Results
Mandelbaum AOSSM 2002, 2003
Protective System
Sensory receptor outflow causes
activation of muscle efferents generating
stabilizing muscle co-contractions
6/12/2013
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Pertubation Training
Selective Muscle Use Patterns
• ↑ co-contraction (Q-H-G)
• ↓ muscle stretch reflex
Protective System
Protective Muscle
Contractions
Knee Joint Resistance
to Deformation
• Always present
• First line of defense
(Relaxed)
Intrinsic Stiffness
• Dependent upon the excitation provided by the alpha and gamma motoneurons.
• Can be modified with training.
Extrinsic Stiffness
Gender Differences in the
Contributions of the Musculature to Knee Shear Stiffness
Edward M Wojtys, MD
James A. Ashton-Miller, Ph.D
Laura J. Huston, M.S.
JBJS, 2002
Males 473%
Females 217%
(p=0.003)
% Increase in Stiffness
6/12/2013
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Strength was not the predominant
contributor to knee stiffness.
Stiffness = -0.009x1 -17.8x2 +0.5x3 + ß
X1 = muscle strength (p=0.974)
X2 = gender (p=0.049)
X3 = subject’s height (p=0.666)
ß = constant = 51.9 (p=0.576)
Regression Model
Gender differences in active musculo -skeletal stiffness
--- Men
--- Women
HamstringsQuads
Female subjects demonstrated a 56-73%reduced active limb stiffness relative to the
male subjects
Granata J Elect & Kines 2002
Hopping Freq. Males Females % Diff
preferred 26 (9) 19 (8) * 27% *
2.5 Hz 31 (8) 24 (5) * 23% *
3.0 Hz 43 (8) 35 (7) * 19% *
* males significantly greater (p<0.05)
Stiffness Results (kN/m)
1. Leg stiffness in the female subjects was approximately 77% that seen in males.
2. Body mass did not adequately explain the gender effect.
Granata, 2002Gender Differences in the Muscular
Protection of the Knee Among BMI-Matched Athletes
JBJS May 2003
Study Hypothesis:No gender differences exist in internal tibial-
femoral rotation when maximally contracting
knee joint musculature.
1. Stimulates joint and muscle receptors to induce high level of Q-H-G co-contractions.
2. Improves whole body and single joint positions to ↓ loads on joints.
3. Plyometrics to improve MRT &TPT.
4. Skill training to isolate ideal movements than will generate lowest joint moments and best position for cutting and jumping.
Ideal ACL Training Program
Lloyd JOSPT 2001
80% reduction in rotatory laxity
with 938 N of compressive force
Rotatory Laxity of the Knee
Wang & Walker JBJS 1974
6/12/2013
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• 200 – 400% increase with isometric contraction
• 1000% increase in conditioned athletes
Varus-Valgus Knee Stiffness
Markolf JBJS 1976
Multifactorial!
Hormones – not understood
Worrisome
Anatomy – difficult to change
Muscle Function – training programs
?? mechanism of action
Causes?
t = 0 t = 200 msec
• Lengthening ?• Isometric ?• Shortening ?
0 0 . 2 0 . 4 0 . 6 0 . 8 1 . 00
0 . 2
0 . 4
0 . 6
0 . 8
1
1 . 2
1 . 4
1 . 6
1 . 8
v
Background
Lengtheninghamstrings produced the lowest relative ACL strain
Effect of Hamstrings
Withrow ORS 2006
Configuration
Mean (SD)
Max ACL
strain
(%)
Max impact
force
(N)
Max quad
force
(N)
Max
medial
hamstring
force (N)
Max
lateral
hamstring
force (N)
Shortening 3.0 (1.1) 1755 (275) 1579 (203) 168 (68) 183 (62)
Lengthening 0.8 (0.6) 2093 (370) 1161 (231) 338 (118) 394 (83)
Isotonic 3.6 (1.1) 1777 (256) 1546 (186) 92 (29) 103 (31)
No hamstring 2.9 (1.3) 1702 (224) 1514 (169) N/A N/A
Lengthening hamstring condition significantly decreased
anteromedial ACL relative strain in this jump landing model
Effect of Hamstrings
Withrow ORS 2006
6/12/2013
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For a given increase in knee flexionangle, an increase in hip flexion angle
exists… that will lengthen the hamstring
muscle-tendon unit (MTU) in a jump
landing.
Lengthening
Contraction≈ 1.6
Isometric
or Shortening
contraction
Hypothesis Methods
• 3 cadavers• Open dissection and digitization of
origins and insertions of BF, SM and ST MTU
• Certus system kinematic measurements
• Calculate hamstring MTU length for knee angles between 0 - 90o at 0, 30 or 60o hip angles (3 trials each)
l Hamstring = f ( θKnee , θHip )
• Initial Knee &
Hip Angle 30°
• At Landing
–Hip ↑ 15°
–Knee ↑ 21°
Pflum 2004
0°30°60°0 2 0 4 0 6 0 8 0
3 3
3 4
3 5
3 6
3 7
3 8
3 9
4 0
4 1
Ham
str
ing L
ength
(cm
)
K n e e F le x i o n A n g le ( d e g )
C a d a v e r # 1 - B FBF
75°°°°60°°°°45°°°°30°°°°0°°°° Hip Angle
Russell et al. J. Athl. Train. 2006
Forward Hop
Conclusions
1. Hypothesis supported: A hamstring lengthening state can indeed occur - when the change in hip angle exceeds 57% of the change in knee angle.
2. Using drop landing test data, simulations suggest the hamstring MTU act in a quasi-isometric state during a drop landing
3. Reducing the knee flexion or increasing the hip flexion will lengthen hamstring MTU to help protect ACL, and vice versa.
0 0 .2 0 . 4 0 .6 0 . 8 1 . 00
0 .2
0 .4
0 .6
0 .8
1
1 .2
1 .4
1 .6
1 .8
Pooled Risk
Risk Ratio – 0.38
Prevention programs reduced risk of ACL tear by 62%
Sadoghi JBJS 2012
6/12/2013
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Pooled Risk - Gender
Female risk reduction – 52%
Male risk reduction – 85%
Number needed to treat to prevent 1 ACL tear was 5-87
Sadoghi JBJS 2012
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