1. Non-Operative Management of
the ACL-Deficient Knee
Conservative Management of ACL
Lecturer:
Eric Robertson, PT, DPT, Assistant Professor
Regis University, Denver, CO
University of Texas at El Paso, El Paso, TX

2. Objectives
• Describe usual care following ACL injury
• Define the terms Copers and Non-Copers
• Describe the characteristics of Copers versus Non-copers
• Explore the impact of psychological factors in prognosis and
outcomes
• Examine outcomes following conservative management of ACL
injury
• Review evidence-based interventions for non-operative
management of the ACL-deficient knee

3. It’s a paradigm
Currently, there are over 80,000 ACL injuries in the U.S.
each year. Over 90% of those will be surgically repaired.
Cochrane SR, 2005, Benjaminse, 2006

4. It’s a paradigm
ACL reconstruction costs $3 billion each year.

5. It’s a paradigm
It‘s not been demonstrated that operative management of
ACL injury is superior to non-operative management.

6. It’s a paradigm
It‘s not been demonstrated that operative management of
ACL injury is superior to non-operative management.

7. It’s really true
Surgical time correlated to $$
23 min = $1000
=
Bonsell, 2000

8. Why do orthopedic surgeons recommend
ACL reconstruction following injury?
• Restore knee stability
• Prevent meniscal damage
• Protect articular cartilage
• Avoid degenerative
changes
• All these are theoretical
concepts, with various
levels of support in
literature.
• Who might be non-
surgical candidates?
• Seasonal, construction
workers
• Athletes with a need to
compete (scholarship,
perhaps?)
• Low activity level
• Is there a way we can figure
out who can function
without an intact ACL?

9. What do we think?
Let‘s have a brief discussion. Is ACL repair a lemon?

10. Risk Factors for post-ACL OA?
• ACL Injury
• ACL Repair
• Opting out of ACL
Repair
• Meniscal Injury
• Meniscetomy at time
of injury or before
• Chondral Lesions

11. OA incidence is the same if you have surgery or if you don‘t.

12. Streich et al, 2011

13. “We observed significantly better knee-stability (P = 0.008)
but more osteoarthritis (Grade II or higher) after ACL-
reconstruction (42% vs. 25%)”
Kessler et al, 2008
“Eleven years after ACL-rupture the physical activity levels
are similar for both groups.”

14. Risk Factors for post ACL OA?
• ACL Injury
• ACL Repair
• Opting out of ACL
Repair
• Meniscal Injury
• Meniscetomy at time
of injury or before
• Chondral Lesions

15. Risk Factors for post ACL OA?
•ACL Injury
• ACL Repair
• Opting out of ACL
Repair
• Meniscal Injury
• Meniscetomy at
time of injury or
before
• Chondral Lesions

16. Risk Factors for post ACL OA?
•ACL Injury
•Stability

17. Stability of the Knee
• Dynamic
• Kinestheic awareness
• Proprioception
• Muscle strength and control
• Balance
• Core Stabilility
• Static
• Ligamentous
• Meniscii
• Ability to achieve screw home mechanism (full extension)

18. Can some people cope without an ACL?
Is there enough dynamic support to stabilize the knee sufficiently for
function?

19. Coper
Those individuals who can dynamically stabilize an
ACLD knee.
• Must resume previous activity
• No episodes of giving way
• Do not require surgery
• Activity persists for up to one year, (perhaps)

20. Non-Coper
Those individuals who can’t dynamically stabilize an
ACLD knee.
• Giving way
• Unable to resume previous level of activity
• Require surgery

21. Note…
Being a coper or a non-coper does not seem to predict
surgical outcomes.
% of ACLR Achieve Full Return to Activity
Copers Non-Copers
8-82% 19-82%

22. Comparing Copers vs Non-Copers
• Kinematic Differences
• EMG Differences
• Functional Differences
• Activity Differences

23. Kinematic Differences
Copers
• Joint stability
• Fewer episodes of giving
way
• Somewhat normal knee
ROM and forces during
functional activities and
gait
Non-Copers
• Increased joint laxity
• Reduced knee ROM
during hop tests
• Reduced knee
compression and shear
forces during gait

24. EMG Differences
Copers
• Poor quadriceps control
• Preferentially utilized a
vastus lateralis and
medial hamstring
activation pattern during
a cutting drill
Non-Copers
• Poor quadriceps control
• Increased quadriceps
activity during knee
flexion activities
• Increased co-contraction
strategies

25. Functional Differences
Copers
• Increased IDKC scores
• Increased fuctional scores
• Improved single-limb hop
tests
Non-Copers
• Reluctance to participate
• Fear avoidance

26. Activity Differences
Copers
• Return to Activity: 82%
• Return to activity is
limited
• Reduced activity scores
~21%
• Self-reports: overall good
knee function
Non-Copers
• Return to Activity: 82%
• Return to activity is
limited
• Reduced activity scores
~21%
• Self-reports: overall good
knee function

27. IDENTIFICATION
Who can cope with ACLD?

28. U of Delaware Screening Examination
Moksnes H, Snyder-Mackler L, Risberg MA. Individuals with an anterior cruciate ligament-deficient knee classified as noncopers may
be candidates for nonsurgical rehabilitation. J Orthop Sports Phys Ther. 2008;38(10):586-95.

29. Identifying Copers (Fitzgerald, 2000)
Potential Copers:
• 1. < 1 episode of giving way
• 2. > 80% 6m timed hop test
• 3. > 80% KOS ADL subscale
• 4. > 60% Global Rating of Knee
Function

30. Prevalence of True Copers
True Copers Non Copers
• Fitzgerald, 2000; Hurd 2008
• 42%
• Moekses
• 37%
• True Copers can return to
function without surgical
reconstruction.
• 63% but…maybe shouldn‘t
classify them right away…
• Of Non-copers, 70% were
classified at Copers at 1-
year follow-up
• Summary: 63% of subjects
were copers
Moksnes H, Snyder-Mackler L, Risberg MA. Individuals with an anterior cruciate ligament-deficient knee classified as noncopers may
be candidates for nonsurgical rehabilitation. J Orthop Sports Phys Ther. 2008;38(10):586-95.

31. When do I measure?
Optimal Evidence-based Time
Frame for Coper Determination:
• After a period of rehabilitation, after 60 days,
before 6 months
• 10 sessions has been a reported treatment duration

32. Psychological Factors!
―Patient psychological factors are predictive of ACL reconstruction
outcomes.‖ Everhart, 2013 Systematic Review

33. Psychological Model of Pain Perception
(Linton and Shaw, 2011)

34. Specific Psychological Pain
Models
(Linton and Shaw, 2011)
• Fear-avoidance
• Acceptance and commitment
• Misdirected problem solving
• Self-efficacy
• Stress-diathesis

35. Specific Psychological Pain
Models
(Linton and Shaw, 2011)
• Fear-avoidance
• Acceptance and commitment
• Misdirected problem solving
• Self-efficacy
• Stress-diathesis

36. Fear-Avoidance Model
(Linton and Shaw, 2011)
• Attention
• Fear/Injury keys attention to internal stimuli (hyper-vigilance)
• Cognition
• This is pain/event catastrophizing
• Emotion
• Fear, depression, and anxiety
• Behavior
• Activity avoidance is hallmark of the model

37. Fear-Avoidance Model
(Leeuw et al, 2007)

38. Misdirected Problem Solving
(Linton and Shaw, 2011)
• Attention
• Continuing pain/condition demands attention
• Cognition
• Beliefs that there is an identifiable cause of pain/circumstance
• Emotion
• Worry is the primary one here
• Behavior
• Attempts (continued) to solve the problem

39. Misdirected Problem Solving
(Eccleston et al, 2007)

40. Self-Efficacy
(Linton and Shaw, 2011)
• Attention
• Not emphasized much in this model
• Cognition
• Beliefs related to locus of control
• Emotion
• Not emphasized much in this model
• Behavior
• Coping skills

41. Self-Efficacy
(Bandura, 1997)
• Model summary
• ―the belief in one‘s capabilities to organize and execute the
courses of action required to produce given attainments‖
• Low self-efficacy accompanied by beliefs that pain/rehab is
uncontrollable
• High self-efficacy may be feature of self-management

42. Low Self-Efficacy Example
• ―I hope the doctor knows what he‘s doing in surgery. I
really need this to go right so I can return to my sport.‖

43. High Self-Efficacy Example
• ―I‘m going to play football again, and quite frankly, I
don‘t care what the doctors say.‖

44. Communication Keys
• Physician research for effective patient communication (Maguire
and Pitceathly, 2002)
• Style and focus
• Eye contact
• Active listening
• Facilitation of self-disclosure
• Patient concerns
• Explicit interest and consideration of psychosocial factors

45. Clinical Application
• Be confident
• Be positive
• Clearly explain the problem in current framework for pain
perception
• Come to an agreement about the nature of the problem and the
way to treat it.

46. Psychologically Informed
Intervention
(Nicholas and George, Phys Ther 2011)
• Model of communication
• Cognitive-behavioral methods

47. Cognitive Behavioral Methods
(Nicholas and George, 2011)
• Analysis
• Observe when/where problem behaviors occur and consequences
• Identify beliefs/expectations associated with problem behaviors
• Develop a formulation of relationships between these domains

48. Cognitive Behavioral Methods
(Nicholas and George, 2011)
• Change plan (involves patient)
• Identify goals the patient wants to achieve
• Breakdown into specific sub-goals that can be up-graded
• Especially important for quota or exposure approaches
• Develop plan for dealing with obstacles
• Plan for reinforcement when successful

49. Cognitive Behavioral Methods
(Nicholas and George, 2011)
• Implement plan
• Explain to patient the formulation of problem behaviors (including
pain) and obtain agreement
• Ensure patients works on upgrading activities that were previously
avoided
• Help patient problem solve obstacles
• Provide skills training as needed
• Monitor and reinforce when successful
• Terminate treatment when goals are met

50. Psychologically Informed
Intervention
(Nicholas and George, Phys Ther 2011)
• Model of communication
• Cognitive-behavioral methods
• Treatment approaches

51. Psychosocial Pain Treatment
(Jensen, 2011)
• Clinical approaches
• Hypnosis
• Relaxation training
• Mindfulness meditation training
• Operant treatment (e.g. graded exercise)
• Graded exposure
• Motivational interviewing
• Cognitive and cognitive behavioral therapies
• Acceptance based cognitive therapy

52. Psychosocial Pain Treatment
(Jensen, 2011)
• Clinical approaches
• Hypnosis
• Relaxation training
• Mindfulness meditation training
• Operant treatment (e.g. graded exercise)
• Graded exposure
• Motivational interviewing
• Cognitive and cognitive behavioral therapies
• Acceptance based cognitive therapy

53. GRADED EXERCISE (ACTIVITY)

54. Fear-Avoidance Model
(Leeuw et al, 2007)

55. Fear-Avoidance Beliefs Assessment
• Fear-Avoidance Beliefs Questionnaire used to screen for
elevated fear-avoidance beliefs (Waddell et al, Pain, 1993)
• ―Physical activity might harm my knee‖ (0-6)
• ―I should not do physical activities which (might) make my pain
worse‖ (0-6)
• ―I do not think I will be back to normal anytime soon‖ (0-6)

56. Kinesiophobia Assessment
• Tampa Scale of Kinesiophobia (TSK) is also used to assess pain-
related fear and fear of re-injury
• Originally 17 items, now an 11 item scale (TSK-11) is
recommended (Woby et al, 2005)
• ―I‘m afraid I might injury myself if I exercise‖ (1 – 4)
• ―Pain always means I have injured my body‖ (1 – 4)

57. Tampa Scale of Kinesiophobia (TSK-11)
(Woby et al, 2005)
SUM

58. Pain Catastrophizing Screening
• Pain Catastastrophizing Scale (PCS) used to screen for elevated
pain catastrophizing (Sullivan et al, 1995).
• ―I worry all the time about whether the pain will end‖ (0-4)
• ―I keep thinking about how much it hurts‖ (0-4)
• ―There‘s nothing I can do to reduce the intensity of the pain‖ (0-4)

59. Pain Catastrophizing Screening
SUM

60. Sport / ACL Specific Measures
of Psychological Factors
• ACL – Return to Sport After Injury scale
• 11-item scale
• ‗‗Are you fearful of reinjuring your knee by playing sport?‘‘ and ‗‗Are you
confident you can perform at your previous level of sports participation?‘‘
• The Incredibly Short Profile of Mood States
• Rate: anxiety, sadness/depression, energy, fatigue, anger on 5-point scale from
―nothing‖ to ―extreme‖
• TSK
• Sport Rehabilitation Locus of Control
• 5-point scale, ―agree‖ or ―disagree with statements
• ‗I‘m in control of my rehabilitation and return to sport‘‘ and ‗‗If it‘s meant to
be, I‘ll get back to sport‘‘
Arden et al, 2013 AJSM

61. Arden et al., 2013
• ―Clinical screening for maladaptive psychological
responses in athletes before and soon after surgery may
help clinicians identify athletes at risk of not returning to
their pre-injury level of sport by 12 months.‖

62. Education Modifications
―…unambiguously educating the patient in a way such
that the patient views his or her pain as a common
condition, rather than as a serious disease that needs
careful protection.‖
(Vlaeyan and Linton, Pain, 2000)

63. When to Intervene?
Injury Return to
Sport
Early after Injury, pre-operatively, and early in rehab process
seems more effective for influencing psychological barriers with
ACL injury

64. Graded Exercise
• Principles
• Based on operant conditioning principles (Fordyce et al, Arch
Phys Med Rehabil, 1973)
• Primary intervention goal is increase in activity through quota
attainment
• Intervention does not focus on symptom abatement

65. Graded Exercise
• Basic treatment flow
• Include a variety of general exercises or activities
• Determine exercise or activity tolerance
• Set quota based on exercise or activity tolerance
• Hold patient accountable to quota attainment
• Reward quota attainment NOT pain behavior
• Goals remain focused on functional gains
• Repeat process

66. GRADED EXPOSURE

67. Fear-Avoidance Model
(Leeuw et al, 2007)

68. Specific Fear
• Vlaeyen et al suggests measurement of specific fears more
relevant to patient
• May be necessary for certain treatment protocols

69. Specific Fear
• Beyond the FABQ or TSK or PCS
• Need to measure fear of specific activities
• PHODA-SeV (Leeuw et al, 2007) (Pictures)
• 20 movements/activities presented to subjects
• Rate fear of each one on VAS (electronically)
• Consider highly rated movements/activities to intervention

70. Fear of Activities
• Fear of Daily Activities Questionnaire (FDAQ) used to identify
fear of specific activities
(George et al, Phys Ther, 2009)
• 10 movements/activities presented to subjects
• Rate fear of each one on VAS
• Average the first 10 items for FDAQ score
• Consider highly rated movements/activities to intervention

71. Scan for
highly rated
activities to
include for
intervention
AVERAGE (10 Items)

72. Graded Exposure
• Vlaeyen et al suggests as a more effective alternative than quota
driven approaches
• What is the difference?
• Graded activity = increase in generic functional capacity (operant
conditioning model)
• Graded exposure = increase in activities that are fearful
(exposure/phobia model)
• Differences have not been tested (much)

73. Graded Exposure
• Basic treatment flow
• Identified activities or exercises that are fearful
• Determine initial exposure level
• Gradually increase exposure based on decreased fear and
anxiety
• Hold patient accountable to increasing exposure
• DO NOT reward pain behavior
• Incorporate exposure as part of home program
• Repeat process

74.  Outcome
High
fearPrognostic factor
Treatment Moderator
High
fear
Treatment
A
Treatment
B
↑ Outcome
 Outcome
Low
fear
Treatment
A
Treatment
B
 Outcome
↑ Outcome
Treatment Mediator
Treatment
Fear
Outcome
Outcome
Decision
Aides
Treatment
Monitoring
Hill and Fritz, Phys Ther, 2011

75. Treatment Moderating Factor
• Makes treatment effect greater in one group vs. another
• When or among whom does an effect ―work‖?
• Source of treatment effect heterogeneity
• Decision Aide
High
fear
Treatment
A
Treatment
B
↑ Outcome
 Outcome
Low
fear
Treatment
A
Treatment
B
 Outcome
↑ Outcome

76. Treatment Mediating Factor
• Mediator variables are part of the mechanism through which
treatment impacts the outcome.
• The effect of treatment on an outcome involves intervening
changes in mediator variable
• Treatment Monitoring
Treatment
Fear
Outcome

77. How about Psychological Factors
and Copers vs Non-Copers?
• Kartigan et al., JOSPT 2013 Nov
• ―Kinesiophobia after ACL Rupture and Reconstruction:
Non-Copers Versus Potential Copers‖

78. Kartigan et al., JOSPT 2013 Nov
• 50 copers
• 61 non-copers
• Examined functional outcomes and kinesiophobia after
injury and 6 months post-surger
• (all copers and non-copers had surgery)

79. Kinesiophobia: Non-copers
Pre-Surgery Post-Op
70
10
*Graphical representation, not real scores

80. Kinesiophobia: Potential Copers
Pre-Surgery Post-Op
30
10
*Graphical representation, not real scores

81. Key points
• Non-copers had higher levels of kinesiophobia pre-
operatively, but greater reductions when measured post-
operatively compared to potential copers.
• Kinesiophobia is higher pre-op than post-op, regardless
of performance on functional measures.
• Kinesiophobia should be measured throughout rehab.
(plateaus at ~6 months?)

82. Components of Rehabilitation Program
• Rehabilitation looks similar to post-operative
rehabilitation and many of the same principles apply
• Optimize quad function
• Minimize swelling
• Maximize ROM
• Neuromuscular re-education

83. Restoring Quadriceps Function
• Quad Sets
• Straight Leg Raises
• With and without
Biofeedback
• Active Knee Extension
Against Gravity: No
Added Resistance

84. Fitzgerald GK, Piva SR, Irrgang JJ. A modified neuromuscular electrical
stimulation protocol for quadriceps strength training following ACL
reconstruction. JOSPT 2003 33(9): 492-501
• 2500hz, 75 burst/sec
• 10 contractions
• 10 on/ 50 off
• Stimulus produces
full, sustained quad
contraction with
evidence of superior
patellar glide
NMES

85. Lower Extremity Strengthening
• Initiate closed chain exercise
with body weight when patient
can fully weight bear without
crutches.
• Double and single leg squats (0-
45)
• Lateral and forward step ups
• Calf raises (up on toes)
• Progress to leg press when
tolerating 3 sets of 15 reps for
two consecutive sessions
without
pain, swelling, instability
• No significant difference in
anterior knee laxity at 6
months
• Significant increase in
quadriceps torque in the
CKC/OKC group
• Significant higher number of
patients returned to pre-injury
sports level in the CKC/OKC
group and did so 2 months
earlier than the CKC group
• Conclusion: Incorporate OKC
exercises with CKC exercises
in the protected ranges
following ACL Reconstruction
Mikkelsen C, Werner S, Eriksson E. Closed kinetic chain alone compared to combined open and closed chain
exercises for quadriceps strengthening after anterior cruciate ligament reconstruction with respect to return to
sports: a prospective matched follow-up study. Knee Surg, Sports Tramatol, Arthrosc. 2000; 8: 337-342.

86. Lower Extremity Strengthening
• Begin leg press with
double leg and
eventually progress to
single leg
• Begin with 50 to 75%
of body weight
Arc of Motion = 0 to 45

87. Restore Balance and Proprioception
• Altered proprioception and
lower extremity muscular
control has been associated
with ACL Injury
• Unclear if these deficits fully
resolve after ACL
reconstruction
• Functional retraining programs
for post-op ACL rehab may
need to emphasize
enhancement of lower
extremity neuromuscular
control strategies

88. Criterion Based Progression
• Running
• Pool Run (week 6)
• Treadmill Run (week 8)
• Normal gait pattern while walking
• Quad strength = 70% of uninvolved limb
• Minimal effusion with minimal pain
Suggested Progression from Adams et al. JOSPT 2012

89. Criterion Based Progression
• Agility Training
• Track or Road Running
for 1 to 2 miles without
pain, swelling, instability
• Quad Strength = 80% of
uninvolved limb
• Begin agility activities
with 50% effort, progress
to 75% then 100% effort
provided no pain,
swelling, instability

90. Criterion Based Progression
• Sprinting
• Tolerating all agility and low level
sport specific training.
• Quad strength 85 to 90% of
uninvolved limb
• Begin with form running at 50 and
75% effort, progress to 100%
when tolerating these without
pain, swelling, instability
• Lower Level Sport Specific
Training
• Tolerating all agility training
at 100% effort without
pain, swellling, or instability
• Quad function = 85% of
uninvolved limb

91. Identifying Copers (Fitzgerald, 2000)
Potential Copers:
• 1. < 1 episode of giving way
• 2. > 80% 6m timed hop test
• 3. > 80% KOS ADL subscale
• 4. > 60% Global Rating of Knee
Function

92. Return to Sport
• Tolerating 100% effort sprinting, agility drills, jumping, and
hopping
• No evidence of compensation or valgus collapse
• No pain or reports of pain as progression continues
• No reports of giving way
• No effusion or signs of inflammation
• Begin with opposed practice of sport specific skills (training
partner)
• Return to practice with team when tolerating opposed practice
of skills.
• Return to sport when no difficulty with all practice activities.

93. Components of Rehabilitation Program
• Include Open-Chain Exercises
• Taggesson, 2008 – no differences btwn OKC/CKC in observed
dynamic tibial translation
• OKC may significantly improve quad strength
• NMES
• Include kinesthetic awareness training
• Include perturbation training
• Enhance ability to protect joint
• Neuromuscular component
• Key Outcome: Resume previous level of activities, usually
within <6 months to 1 year.

94. Bracing
• Functional knee bracing does not seem to improve
proprioception following ACL reconstruction even
at 2 years after surgery.
• Bracing produced significantly more thigh atrophy
at 3 months after surgery than did non-bracing.
• Bracing does not appear to influence either
objective stability or subjective function.
• Some researchers have concluded that functional
braces may expose athletes to additional risk by
imparting a false sense of confidence.

95. A note about joint health…
• One study reported a reduced rate of surgery using
conservative therapy and optional ACLR, however…
• Increased rates of meniscal tear/damage noted
• Rates of Knee OA increased with ACL injury regardless
of management decision

96. Choosing Surgery
• Remains gold standard for
athletes, especially higher
level, requiring pivoting skill
• Complex and multifactorial for
everyone else
• Choosing surgery not correlated
with better outcomes

97. It’s a paradigm
Currently, there are over 80,000 ACL injuries in the U.S.
each year. Over 90% of those will be surgically repaired.
Cochrane SR, 2005, Benjaminse, 2006

99. References:
• Eitzen, Ingrid, Havard Moksnes, Lynn Snyder-Mackler, Lars Engebretsen, and May Arna Risberg. ―Functional Tests Should Be Accentuated
More in the Decision for ACL Reconstruction.‖ Knee Surgery, Sports Traumatology, Arthroscopy: Official Journal of the ESSKA (April
22, 2010). doi:10.1007/s00167-010-1113-5.
• Fitzgerald, G K, M J Axe, and L Snyder-Mackler. ―A Decision-making Scheme for Returning Patients to High-level Activity with
Nonoperative Treatment after Anterior Cruciate Ligament Rupture.‖ Knee Surgery, Sports Traumatology, Arthroscopy: Official Journal of
the ESSKA 8, no. 2 (2000): 76–82.
• ———. ―Proposed Practice Guidelines for Nonoperative Anterior Cruciate Ligament Rehabilitation of Physically Active Individuals.‖ The
Journal of Orthopaedic and Sports Physical Therapy 30, no. 4 (April 2000): 194–203.
• ———. ―The Efficacy of Perturbation Training in Nonoperative Anterior Cruciate Ligament Rehabilitation Programs for Physical Active
Individuals.‖ Physical Therapy 80, no. 2 (February 2000): 128–40.
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Anterior Cruciate Ligament Tears.‖ The New England Journal of Medicine 363, no. 4 (July 22, 2010): 331–342.
doi:10.1056/NEJMoa0907797.
• Frobell, Richard B, Harald P Roos, Ewa M Roos, Frank W Roemer, Jonas Ranstam, and L Stefan Lohmander. ―Treatment for Acute Anterior
Cruciate Ligament Tear: Five Year Outcome of Randomised Trial.‖ BMJ (Clinical Research Ed.) 346 (2013): f232.
• Grindem, Hege, Ingrid Eitzen, Håvard Moksnes, Lynn Snyder-Mackler, and May Arna Risberg. ―A Pair-matched Comparison of Return to
Pivoting Sports at 1 Year in Anterior Cruciate Ligament-injured Patients after a Nonoperative Versus an Operative Treatment Course.‖ The
American Journal of Sports Medicine 40, no. 11 (November 2012): 2509–2516. doi:10.1177/0363546512458424.
• Grindem, Hege, David Logerstedt, Ingrid Eitzen, Håvard Moksnes, Michael J Axe, Lynn Snyder-Mackler, Lars Engebretsen, and May Arna
Risberg. ―Single-legged Hop Tests as Predictors of Self-reported Knee Function in Nonoperatively Treated Individuals with Anterior
Cruciate Ligament Injury.‖ The American Journal of Sports Medicine 39, no. 11 (November 2011): 2347–2354.
doi:10.1177/0363546511417085.
• Hurwitz, D E, T P Andriacchi, C A Bush-Joseph, and B R Bach Jr. ―Functional Adaptations in Patients with ACL-deficient Knees.‖ Exercise
and Sport Sciences Reviews 25 (1997): 1–20.

100. References:
• Irrgang, J J, and G K Fitzgerald. ―Rehabilitation of the Multiple-ligament-injured Knee.‖ Clinics in Sports Medicine 19,
no. 3 (July 2000): 545–71.
• Lewek, Michael D, Terese L Chmielewski, May Arna Risberg, and Lynn Snyder-Mackler. ―Dynamic Knee Stability
after Anterior Cruciate Ligament Rupture.‖ Exercise and Sport Sciences Reviews 31, no. 4 (October 2003): 195–200.
• Mihelic, Radovan, Hari Jurdana, Zdravko Jotanovic, Tomislav Madjarevic, and Anton Tudor. ―Long-term Results of
Anterior Cruciate Ligament Reconstruction: a Comparison with Non-operative Treatment with a Follow-up of 17-20
Years.‖ International Orthopaedics 35, no. 7 (July 2011): 1093–1097. doi:10.1007/s00264-011-1206-x.
• Moksnes, H, and M A Risberg. ―Performance-based Functional Evaluation of Non-operative and Operative Treatment
after Anterior Cruciate Ligament Injury.‖ Scandinavian Journal of Medicine & Science in Sports 19, no. 3 (June 2009):
345–355. doi:10.1111/j.1600-0838.2008.00816.x.
• Moksnes, Håvard, Lars Engebretsen, Ingrid Eitzen, and May Arna Risberg. ―Functional Outcomes Following a Non-
operative Treatment Algorithm for Anterior Cruciate Ligament Injuries in Skeletally Immature Children 12 Years and
Younger. A Prospective Cohort with 2 Years Follow-up.‖ British Journal of Sports Medicine 47, no. 8 (May 2013):
488–494. doi:10.1136/bjsports-2012-092066.
• Moksnes, Håvard, Lars Engebretsen, and May Arna Risberg. ―The Current Evidence for Treatment of ACL Injuries in
Children Is Low: a Systematic Review.‖ The Journal of Bone and Joint Surgery. American Volume 94, no. 12 (June 20,
2012): 1112–1119. doi:10.2106/JBJS.K.00960.
• Moksnes, Håvard, Lynn Snyder-Mackler, and May Arna Risberg. ―Individuals with an Anterior Cruciate Ligament-
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