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  • MECHANISM AND PREVENTION OF ANTERIOR CRUCIATE LIGAMENT INJURIES IN

    SPORT

    Cyril J. Donnelly, M.Sc.

    This thesis is presented for the degree of Doctor of Philosophy at The University of Western

    Australia

    The School of Sport Science, Exercise and Health Biomechanics

    June, 2012

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    To my mother and father

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    Abstract

    Review of the anterior cruciate ligament (ACL) injury prevention literature has shown

    that exercise/training can be used to reduce ACL injury risk and injury rates in general

    athletic populations. However, a large gap still exists in the literature, with little to no

    research testing the effectiveness of these prophylactic training protocols in community

    level training environments. Results from this thesis have shown that when

    prophylactic training protocols were implemented in community level training

    environments; they were not effective in reducing surrogate biomechanical measures

    of ACL injury risk like peak knee joint loading and muscular support. We must begin to

    better understand the biomechanical mechanisms by which prophylactic training

    protocols act if we can more effectively translate positive laboratory based findings to

    community level training environments.

    To identify these causal mechanisms, we have developed a novel computational

    method capable of identifying causal links between an athlete’s whole-body kinematics

    and knee joint kinetics during dynamic simulations of human movement. The

    generalised kinematic strategy identified during sidestepping, where one half of non-

    contact ACL injuries have been shown to occur was to reposition an athlete’s whole-

    body centre of mass medially, towards their desired direction of travel. Through the

    development and use of these methods, the ability to identify short, concise and

    effective training protocols is possible; increasing the probability of translating ACL

    focused research into injury prevention practice in community level training

    environments.

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    REFERENCE DISCLAIMER

    This PhD dissertation has in part been submitted or accepted for publication in

    internationally recognised journals. For the chapters within this thesis that have been

    submitted, or accepted for publication, referencing will be as per the individual journal

    guidelines. For chapters that have not been submitted for peer review, the referencing

    format will be as per the Journal of Biomechanics.

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    EXECUTIVE SUMMARY

    A) Chapter 2

    Title: An anterior cruciate ligament injury prevention framework: Incorporating the

    recent evidence

    A comprehensive review of the ACL injury prevention literature shows that

    exercise/training can be used to reduce ACL injury risk and injury rates in general

    athletic populations. Though a rationale to use various exercise protocols to reduce

    ACL injuries is established, the mechanisms by which it acts are relatively unknown.

    Using the six stage injury prevention model to ‘Translate Research into Injury

    Prevention Practice’ (TRIPP model), an injury prevention framework specific to, and

    detailed for non-contact ACL injuries was developed. Additionally an empirically based

    rationale for the design of ACL injury prevention training protocols was also developed.

    Within our ACL injury prevention framework, we used a multidisciplinary approach to

    develop a model for the aetiology of ACL injuries, and in turn appropriate

    countermeasures to reduce injury risk. From previously published empirical research,

    three biomechanically based countermeasures were identified:

    1) Reduce the magnitude of externally applied flexion, valgus and internal rotation

    knee moments during the weight acceptance phase of sidestepping or single-

    leg landing.

    2) Increase muscular support against these aforementioned joint moments.

    3) Increase knee flexion angle and the neuromuscular control of the hip during the

    weight acceptance phase of sidestepping and single-leg landing.

    Previous literature has shown that the combined effects of plyometric, balance,

    resistance and/or technique training are effective in reducing the biomechanical risk

    factors associated with ACL injury in ‘ideal’ training environments. However, a large

    gap exists in the literature, where little to no research has tested the effectiveness of

    these prophylactic training protocols in ‘real-world’ training settings. It is then unknown

    if positive laboratory based biomechanical training outcomes can be translated to

    community level training environments. Additionally, it is evident that the use of

    feedback within this framework is needed to determine how biomechanical factors, like

    joint loading and muscle support are targeted following a given training intervention. It

    is by identifying these causal links that more effective and targeted ACL injury

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    prevention training programs can be developed and in turn lead to reduced ACL injury

    rates in the future.

    The overall goal of this thesis is to begin filling these gaps and determine if positive

    laboratory based findings can be transferred to ‘real-world’ community level training

    environments. Additionally, we have developed novel computational methods to

    identify causal relationships between an athlete’s sidestepping and single-leg landing

    techniques, knee joint loading and ACL injury risk. Through this approach, better

    injury prevention protocols targeting the biomechanical factors associated with ACL

    injury can be developed; transferring positive laboratory based training effects to ‘real-

    world’ training environments, and in turn reduce ACL injury rates in community level

    training environments.

    B) Chapters 3 & 4

    Titles:

    Part 1 – Changes in knee joint biomechanics following balance and technique training

    and a season of Australian Football

    Part 2 – Changes in muscle activation following balance and technique training and a

    season of Australian Football

    Purpose: Determine if balance and technique training (BTT) implemented adjunct to

    normal Australian football (AF) training reduces external knee loading and influences

    the activation of muscles crossing the knee during sidestepping. Also, determine if an

    athlete’s knee joint biomechanics and muscle activation changes over a season of AF.

    Finally, determine if changes in muscle activation were proportional to changes in knee

    joint loading.

    Methodology: 1,001 males volunteered to participate in either 28 weeks of BTT or

    ‘sham’ training (ST), adjunct to their normal pre-season and regular training. A subset

    of 34 athletes (BTT, n = 20; ST, n = 14) were randomly recruited for laboratory-based

    biomechanical testing in weeks -1 to 7 and 18 to 25 of the 28 week training

    intervention. During biomechanical testing, participants completed a series of running,

    pre-planned (PpSS) and unplanned sidestepping (UnSS) tasks. During PpSS and

    UnSS, knee joint kinetics in three degrees of freedom and knee flexion kinematics were

    calculated from all 34 athletes. Directed co-contraction ratios (DCCR) in three degrees

    of freedom and total muscle activation (TMA) during PpSS and UnSS were attained

    from 28 (BTT, n = 12; ST, n = 16) of the 34 athletes. A linear mixed model (α = 0.05)

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    was used to determine if knee joint kinematics, kinetics and muscle activation during

    PpSS and UnSS were influenced by 28 weeks of BTT and/or a season of AF.

    Results: The main findings from these studies were that BTT, when implemented

    adjunct to normal ‘real-world’ AF training, was not effective in reducing a player’s knee

    joint kinematics, external knee loading or changing the activation of the muscles

    crossing the knee during PpSS and UnSS. However, significant within season training

    effects were observed. Peak internal rotation knee moments during PpSS significantly

    decreased (p = 0.025) by 45% over a season of AF, while peak valgus knee moments

    during UnSS significantly increased (p = 0.022) by 31%. Additionally, significant

    increases in knee extensor (p = 0.023) and semimembranosus (p = 0.006) muscle

    activation were observed during both PpSS and UnSS. However, TMA was lower

    during UnSS when compared with PpSS, even in the presence of significantly elevated

    valgus knee moments.

    Conclusions: BTT was not effective in changing an athlete’s knee joint biomechanics

    or muscle activation during sidestepping when conducted in ‘real-world’ training

    environments. Following a season of AF, athletes are better able to support both

    frontal and sagittal plane knee loading during PpSS and UnSS. Knee joint

    biomechanics respond to normal AF training differently during pre-planned and

    unplanned sidestepping. Both pre-planned and unplanned sport tasks are therefore

    recommended when assessi