Understanding and Preventing Noncontact ACL Injuries American Orthopaedic Society for Sports Medicine Note: This e-book reproduces the text of the printed book, but it may not include images, tables, or figures that have restrictions on electronic distribution. Understanding and Preventing Noncontact ACL Injuries American Orthopaedic Society for Sports Medicine Editors Timothy E. Hewett Sandra J. Shultz and Letha Y. Griffin Human Kinetics Library of Congress Cataloging-in-Publication Data Understanding and preventing noncontact ACL injuries / American Orthopaedic Society for Sports Medicine ; Timothy E. Hewett, Sandra J. Shultz, Letha Y. Griffin, editors. p. ; cm. Includes bibliographical references and index. ISBN-13: 978-0-7360-6535-1 (hard cover) ISBN-10: 0-7360-6535-0 (hard cover) 1. Anterior cruciate ligament--Wounds and injuries--Prevention. 2. Sports injuries-- Prevention. 3. Knee--Wounds and injuries--Prevention. I. Hewett, Timothy E. II. Shultz, Sandra J., 1961- III. Griffin, Letha Y. IV. American Orthopaedic Society for Sports Medicine. [DNLM: 1. Anterior Cruciate Ligament--injuries. 2. Athletic Injuries--prevention & control. 3. Knee Injuries--prevention & control. WE 870 U55 2007] RD561.U53 2007 617.4’7044--dc22 2006038700 ISBN-10: 0-7360-6535-0 (print) ISBN-10: 0-7360-9088-6 (Adobe PDF) ISBN-13: 978-0-7360-6535-1 (print) ISBN-13: 978-0-7360-9088-9 (Adobe PDF) Copyright © 2007 by American Orthopaedic Society for Sports Medicine All rights reserved. Except for use in a review, the reproduction or utilization of this work in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including xerography, photocopying, and recording, and in any information storage and retrieval system, is forbidden without the written permission of the publisher. The Web addresses cited in this text were current as of January 12, 2007, unless otherwise noted. Acquisitions Editor: Loarn D. 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Box 300 226 Albany, North Shore City, Auckland 0064 9 448 1207 e-mail: [email protected] Contents Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xvii Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix An Introduction to Understanding and Preventing ACL Injury . . . . . . xxi Timothy Edwin Hewett, PhD, FACSM The incidence of anterior cruciate ligament (ACL) injuries in young athletes (<25 years of age) remains high. Despite early recognition, initial appropri- ate care, adequate surgical stabilization (if needed), and a well-structured rehabilitation program, arthritis of the injured knee frequently develops. Therefore, prevention strategies to decrease its incidence are needed. This book presents the latest research on the causes and prevention of ACL injuries, particularly among female athletes. In particular, we review the effects of programs that have been recently developed to prevent ACL injury and address the following questions: What are the essential components of effective programs? What do the various programs have in common, and can one assume that these shared components are, therefore, the essential components of an ACL prevention program? How do these programs favor- ably alter neuromuscular risk factors; or, stated in an alternative way, how do they influence biomechanics to decrease risk? What new information on risk factors has come forth that could be used to improve or broaden our present thoughts on prevention strategies or more reliably identify those at increased risk of sustaining an ACL injury? Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xxviii Part I The Problem of ACL Injuries 1 Part Editor: Letha Y. Griffin, MD, PhD Chapter 1 Incidence of ACL Injury . . . . . . . . . . . . . . . . . . . . . . . 5 Stephen W. Marshall, PhD; Darin Padua, PhD, ATC; and Melanie McGrath, MS, ATC The goal of this chapter is to examine advances in data collection and changes in incidence data regarding noncontact ACL injury. Significant progress has been made in the last five years in developing mechanisms to collect more detailed information on ACL injuries, particularly at the collegiate level. Despite initiation of prevention efforts, the overall risk of ACL injuries in collegiate female soccer and basketball has not declined since 1998, and the risk is still three to four times that of male counterparts in these sports. Anterior cruciate ligament injuries also are a concern in other contact (football) and noncontact (gymnastics) sports; prevention efforts should be focused on these activities as well. Rule modifications implemented at the sport governing board level may be another way to enhance prevention efforts, particularly in contact situations. v vi Contents Human Movement and ACL Injury. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 What Is Incidence? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 What Is the Average Incidence of ACL Injury in the General Population? . . . . . . . . . . . . 7 National Ambulatory Care Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 How Does ACL Injury Incidence Vary by Age and Gender?. . . . . . . . . . . . . . . . . . . . . . . 9 How Does the Incidence of ACL Injury Vary by Sport and Gender? . . . . . . . . . . . . . . . 12 Literature Review Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Abstraction of Incidence Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 General Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Synthesis and Commentary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Recommendations for Future Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Chapter 2 Does ACL Reconstruction Prevent Articular Degeneration? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 The ACL Risk Equation Paul H. Marks, MD; Kurt P. Droll, MD, MSc, FRCSC; and Michelle Cameron-Donaldson, MD Osteoarthritis is found more commonly in the knee than in any other weight-bearing joint in the human body. Individuals with ACL insuffi- ciency have been found to have a higher risk for developing osteoarthritis in the knee compared to the general population. Several risk factors have been implicated in the development of osteoarthritis in the ACL-deficient knee, including concomitant meniscal pathology, osteochondral pathol- ogy, impaired proprioception, and biomechanical mediators. The chapter reviews the evidence pertaining to these risk factors. In addition, in an effort to aid in the future prognosis of posttraumatic osteoarthritis, we propose that an “ACL risk equation” be developed that would express overall osteoarthritis risk quantitatively. This proposed equation would be a function of all the pertinent risk factors. Meniscal Pathology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Osteochondral Pathology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Impaired Proprioception. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Biochemical Mediators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Summary and Future Work. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Chapter 3 The Costs Associated With ACL Injury. . . . . . . . . . . 47 Timothy Edwin Hewett, PhD, FACSM; and Bohdanna T. Zazulak, DPT, MS, OCS In this chapter, we review the financial and emotion burdens placed on individuals, families, and societies from ACL injuries. We compare these costs with the amount of federal funding that has been expended to research ACL injuries and their prevention. We also present an analysis of the potential savings that would occur if ACL injury prevention programs were instituted on a more extensive basis. It is concluded that greater awareness Contents vii at both the governmental and public levels is needed to enhance efforts to reduce the incidence of ACL injury. Who Pays for ACL Injury Prevention in the High-Risk Female Athlete?. . . . . . . . . . . . . 52 Informing the High-Risk Female Athlete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Part II ACL Injury Prevention Programs 57 Part Editor: Timothy Edwin Hewett, PhD, FACSM Chapter 4 Components of Prevention Programs. . . . . . . . . . . . . 61 Holly J. Silvers, MPT Twelve ACL intervention programs that have empirically evaluated outcomes were identified. A component analysis of these programs was performed to identify some of the commonalities among successful ACL intervention protocols. Numerous deficits have been identified in the high- risk female adolescent population. These include faulty landing kinematics (hip and knee extension with valgus perturbation), decreased core stability, decreased hamstring contraction times, decreased hamstring and abductor dynamic control, excessive tibial torsion, and subtalar pronation. The exist- ing programs focus on neuromuscular and proprioceptive interventions in the female athletic population in order to reduce the rate of ACL injury in this population. The commonalities of successful programs are discussed. Chapter 5 Theories on How Neuromuscular Intervention Programs May Influence ACL Injury Rates . . . . . . . . 75 The Biomechanical Effects of Plyometric, Balance, Strength, and Feedback Training Timothy Edwin Hewett, PhD, FACSM; Gregory D. Myer, MS, CSCS; and Kevin R. Ford, MS A systematic review of the published literature yielded six studies of interven- tions targeted toward knee or ACL injury prevention in female athletes. Five of the six interventions were reported to reduce injury incidence, four of the six reduced knee injury incidence, and three of the six reduced ACL injury incidence in females. Examination of the similarities and differences among the training regimes gives insight into the development of more effective and efficient interventions. The purpose of this review is to highlight the relative effectiveness of these interventions in altering landing techniques and dynamic balance, as well as the common components of the training. This review focuses on the common components of the various interventions in order to discuss their potential to reduce ACL injury risk and assess their potential for combined use in more effective and efficient intervention protocols. Single-Component Training. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Multicomponent Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Effects of a Comprehensive Program Combined With Either Plyometric or Balance Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 Conclusions and Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 viii Contents Chapter 6 Preventive Training Programs . . . . . . . . . . . . . . . . . . 91 Changing Strength Ratios Versus Positions of Muscular Effi ciency Sandra J. Shultz, PhD, ATC, CSCS Considering the strain patterns and the observed neuromuscular and biomechanical differences noted in males and females, injury prevention programs have attempted to improve both movement strategies and neu- romuscular coordination and strength patterns to reduce these injurious forces. This chapter focuses on the potential for these programs to affect agonist–antagonist muscle strength ratios that may improve knee stability and reduce ACL injury risk. Thigh Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Hip Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Core Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Chapter 7 Effect of Prevention Programs on Performance . . . . 103 Christopher M. Powers, PhD, PT; Christine D. Pollard, PhD, PT; and Susan M. Sigward, PhD, PT, ATC To address resistance from coaches and players as to participating in ACL injury prevention programs and program evaluation, the performance enhancement aspects of these programs are often emphasized. We review the limited data relating to the premise that ACL injury prevention pro- grams improve performance or the key elements underlying performance. We conclude that the evidence to support this premise is inconsistent and that the literature is characterized by a small number of studies, moderate sample sizes with no control group data, and utilization of variable train- ing programs. On the other hand, various forms of training (not related to ACL injury prevention) have been shown to reliably improve the basic components of sport performance. It therefore stands to reason that ACL injury prevention programs should be able to accomplish the same results given an adequate stimulus for a given outcome of interest. Much more high-quality research, however, is needed to verify this speculation. Performance Measure: Vertical Jump Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 Performance Measures: Agility, Strength, and Lunge Distance . . . . . . . . . . . . . . . . . . . 105 Performance Measures: Vertical Jump Height, Single-Leg Hop, Speed, and Strength . . . 106 Performance Measure: Single-Limb Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Performance Measures: Balance, Strength, Single-Leg Hop, Triple Jump, and Stair Hop. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Chapter 8 Congruence Between Existing Prevention Programs and Research on Risk Factors and Mechanisms of Noncontact ACL Injury . . . . . . . . . . . . . . . . . . . . . . 109 William E. Garrett, Jr., MD, PhD; and Bing Yu, PhD In order to develop effective prevention programs, we must know how the injury happens, know what is injured, identify the risk factors, be able Contents ix to study the injury in the lab, try to devise prevention strategies, test the prevention strategies, and continually revise the prevention strategies. The prevention programs that have been developed to date target known risk factors, yet several unanswered questions remain. For example, do these training effects generalize to the competitive situation? Do they lead to long- term behavior change? Do they have sufficient power for a reasonable effect size? Do they address potentially important but unexplored variables such as stretching and endurance? Finally, must these programs be completed exactly as prescribed, or can they serve as suggestions for a variety of activities? This chapter explores possible answers to these questions and proposes one central skill that may be the most effective in reducing injury incidence. ACL-Loading Mechanisms and Risk Factors for Noncontact ACL Injury. . . . . . . . . . . 109 Current Training Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Future Training Program Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Chapter 9 Discussion, Summary, and Future Research Goals . . 121 Lars Engebretsen, MD, PhD This chapter summarizes issues related to successful prevention programs that have recently been evaluated. This includes a discussion of the nature of interventions (cognitive and psychomotor approaches), delivery mecha- nisms, duration, and follow-up. In addition, we offer suggestions regarding needs for future prevention programs. Part III Biomechanical and Neuromuscular Mechanisms of ACL Injuries 129 Part Editor: Timothy Edwin Hewett, PhD, FACSM Chapter 10 Biomechanics Associated With Injury. . . . . . . . . . . 131 Athlete Interviews and Review of Injury Tapes Tron Krosshaug, PhD; and Roald Bahr, MD, PhD A precise description of the biomechanics associated with injury—the injury mechanism—is a key component to understanding the causes of any particular injury type in sport. However, any attempt to describe the injury mechanisms raises a number of issues. A complete understanding of injury causation needs to take into account the multifactorial nature of sport injuries—not only the injury biomechanics, but also the risk factors associated with an increased risk of injury. This chapter reviews studies aimed at assessing multiple variables associated with the specific event in which a noncontact ACL injury occurred, including studies in which athletes have been interviewed about their recollection of these variables and studies in which videotapes of injury events have been analyzed. Defining “Injury Mechanisms”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Describing the Inciting Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Research Approaches to Describe the Injury Mechanisms . . . . . . . . . . . . . . . . . . . . . . 134 Literature Search. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Athlete Interviews. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 x Contents Video Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 Chapter 11 Clinical Biomechanical Studies on ACL Injury Risk Factors . . . . . . . . . . . . . . . . . . . . . 141 Laura J. Huston, MS This chapter reviews clinical studies that have investigated the biome- chanics of ACL injury. It is concluded that kinematic and kinetic gender differences exist that may render women more susceptible than men to ACL injury. The most prevalent differences that females exhibited, either when landing from a jump or during a cutting and pivoting maneuver, were reduced hip and knee flexion angles, increased knee valgus, internal rota- tion of the femur, high quadriceps activity unbalanced by the hamstrings, and inadequate generation of trans-knee muscle stiffness. Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 Kinematic and Kinetic Differences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Jump Landings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Sidestep and Cutting Maneuvers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Muscular Differences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 Chapter 12 Effects of Neuromuscular Training on Lower Extremity Motion Patterns . . . . . . . . . . . . . . 155 Bing Yu, PhD; and Marlene DeMaio, MD Understanding the biomechanical changes following training programs is critical in the development of intervention strategies for reducing the risk of sustaining noncontact ACL injuries. Scientifically evaluating the effectiveness of these training programs is difficult. It is helpful to have a good understand- ing of the effects of various exercises on the biomechanics of the movements in those athletic tasks in which noncontact ACL injuries frequently occur. Such understanding will not only assist clinicians and scientists in deciding which exercises to include in intervention programs, but also provide indirect evidence to support the effectiveness of intervention programs. Biomechani- cal studies with sophisticated modeling techniques to estimate in vivo ACL loading in athletic tasks are particularly needed to elucidate cause-and-effect relationships between movements and ACL loading and injuries. These types of biomechanical studies will be critical tools for identifying specific motor control–related biomechanical risk factors, as well as for evaluating interven- tion programs aimed at reducing the risk of noncontact ACL injuries. Combined Training Programs Including Plyometrics . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 Chapter 13 Sport-Specific Injury Mechanisms Associated With Pivoting, Cutting, and Landing. . . . . . . . . . . . 163 Mary Lloyd Ireland, MD The typical mechanism of ACL injury in basketball, soccer, and team handball is a rapid but awkward stop and anticipation of lateral move-