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Anterior Cruciate Ligament (ACL) Injury Prevention

Original Editors - Stephanie Geeurickx, Kevin Campion, Aarti Sareen as part of the Vrije Universiteit Brussel Evidence-Based Practice Project

Top Contributors - Vidya Acharya and Alexandra Stead

Introduction

Injuries to the ACL are relatively common knee injuries among athletes.[1] They occur most frequently in those who play sports involving pivoting (e.g. football, basketball, netball, soccer, European team handball, gymnastics, downhill skiing). They can range from mild (such as small tears/sprain) to severe (when the ligament is completely torn). Both contact and non-contact injuries can occur, although non-contact tears and ruptures are most common when the limb is in non contact and combined with valgus and internal rotation trauma It appears that females tend to have a higher incidence rate of ACL injury than males, that being between 2.4 and 9.7 times higher in female athletes competing in similar activities[2][3][4][5], and an acute rupture of ACL is a common trauma, it is incidence up to 84/ 100000 persons in USA, 78/100000 persons for sweden with 32 years is the mean age of injury[6].

Management

Please see Anterior Cruciate Ligament (ACL) Reconstruction

Please see Anterior Cruciate Ligament (ACL) Rehabilitation

Surgical or non-surgical management after an ACL tear is analyzed through systematic reviews and meta-analyses, where the absolute best standard of empirical research of the outcome of interventions is assessed. [7] Recent evidence based reviews have found similar results in both conservative and surgical approach groups with reference to pain levels, symptoms, function, return to sport participation, quality of life, following meniscal tear and surgery rates, and radiographic osteoarthritis of knee (OA) prevalence [8][9].

Injury Prevention

ACL injury rates appear to be on the increase and it is of concern that recent reports show the rates of ACL injury to have grown most rapidly at the younger end of the age spectrum. Therefore, it is timely to revisit the efficacy of ACL injury prevention training programs and critically evaluate the state of the current evidence for their effectiveness.[10]


Rates of non-contact ACL injury are higher among females than males. Several factors have been identified to explain this sex disparity. Gender differences have been found in motion patterns, positions, and muscular forces generated with various lower extremity coordinated activities. Anatomic and hormonal factors, such as a decrease in ACL circumference, a small and narrow intercondylar notch width, generalised and specific knee joint laxity and a pre-ovulatory phase of menstrual cycle in females, have been discussed as increased risk factors for non-contact ACL injuries.[11][12]

However, modifying these particular risk factors is difficult if not impossible. In contrast, evidence indicates that neuromuscular risk factors are modifiable. Neuromuscular risk factors such as knee valgus position, muscular control (quadriceps and hamstrings muscular activation) and hip and trunk controls have been increasingly implicated in this injury aetiology. .[11][13] 

Implementing an ACL injury prevention program can be extremely beneficial for all patients. Keep in mind that this program will not prevent ACL tears from occurring but can help decrease the risk. There are five key steps that should be included in the planning of this program: 

  • Identification.
  • Exercises.
  • Training load and volume.
  • Training Frequency.
  • Exercise timing.

Most ACL injuries occur when an anterior force is applied to the tibia. It is important to identify the risk factors that can contribute to this anterior force to reduce the chance of injury. Identification of risk factors and mechanisms of injury that are modifiable through neuromuscular based injury prevention programs would allow many athletes to continue sports participation and reduce risk for ACL injury. These modifiable risk factors are sorted into four different categories, including movement and alignment, strength, ground reaction forces (GRFs) and fatigue.

  • Movement and Alignment – There are certain movement and alignment factors that can predispose a patient to an ACL tear, such as landing from a jump with a small knee flexion angle and larger knee valgus angle, decreased active and passive controls of the knee, and dynamic knee valgus positioning.
  • Strength – Muscle weakness is another modifiable risk factor, specifically weak gluteus medius, gluteus minimus, quadriceps, hamstrings and hip abductor muscles.
    • Weakened quadriceps may decrease knee flexion control.
    • Weak hamstrings and hip abductors may lead to an increased valgus load on the knee. 
    • Weak core musculature will lead to decreased trunk stability and/or lateral pelvic movement.
  • GRFs – If a patient has weak hamstrings or quadriceps, it may be hard for them to control GRF, which leads to a greater load on the ACL. 
  • Fatigue – Fatigue leads to loss of motor control, especially with the landing phase of a jump.

In 2018,  Arundale, Bizzini, Giordano et al.[14] published Clinical Practice Guidelines (CPG) reviewing the latest injury prevention programs for ACL and knee ligament injuries. The results were extremely positive and state that “there is robust evidence for the advantages of exercise-based knee injury prevention programs, including reduction in risk for all knee injuries and for ACL injuries specifically, with little risk of adverse events and minimal cost” 

Exercise-based prevention was defined as an intervention requiring the participant(s) to be active and move. This includes physical activity, strengthening, stretching, neuromuscular, proprioceptive, agility, or plyometric exercises and other training modalities. But it excludes passive interventions like bracing or programs that only involve education. 

Recommendations

  • It is recommended to implement this exercise-based knee injury prevention programs in athletes for prevention of knee and ACL injuries.
  • This program should be implemented prior to training sessions or games i.e. as a part of warm-up.
  • This CPG identifies three high risk populations and outlines different program most suited for each:
  1. Female athletes <18 years of age: PEP, Sportsmetric ,[15] Harmoknee,[16] Olsen et al,[17] Petersen et al.
  2. Soccer players, especially women: Caraffa et al,[18] Sportsmetric. [15]
  3. Male and female handball players, particularly 15-17 years of age: Olsen et al ,[17] Achenbach et al.[19]
  • Dosage and Delivery: For all programs, the advice is that they ought to involve multiple components, have a session duration >20 minutes, have a weekly training volume >30 minutes, start at pre-season and continue throughout the season with high compliance.
  • The most supported programs involved multiple components such as:
  1. Flexibility - Quadriceps, hamstrings, hip adductors, hip flexors, & calf muscles.
  2. Strengthening - Double-leg squats, single-leg squats, lunges, Nordic hamstring exercise.
  3. Plyometrics - Single leg hopping anterior & posterior, ice skaters, jump to header or catching a ball overhead.
  4. Balance & agility.
  5. Running - Forward & backwards, zigzag running, bounding forward & backwards.
  • This CPG actually provides strong evidence to suggest that exercise-based prevention programs reduce the risk of all knee injuries, not just ACL injuries. “The pooled incident rate ratio indicated that exercise-based prevention programs are effective in reducing the incidence of knee injuries (0.73, 95% confidence interval)” (Arundale, Bizzini, Giordano et al., 2018).[14] For ACL specifically, the programs are also effective in reducing injury but the pooled ratio rate is lower ranging between 0.38-0.49. 
  • This information within this CPG includes all knee injuries, not just ACL injuries. The evidence and recommendations from this CPG should be used to educate and support coaches, parents, athletes and clinicians to incorporate exercise-based injury prevention programs into their training methods. It seems really important to ensure that this message reaches our young female athletes as they have been identified within each high risk population. Even though three high risk populations were identified, these recommendations should be implemented for all young athletes, particularly 12-25 years of age in high risk sports such as rugby, AFL, netball, soccer, basketball and skiing.

Phase I- dynamic warm up

Warm ups and cool downs are a critical part of a training program. The purpose of the dynamic warm-up phase is to allow the athlete to prepare for activity and it greatly reduces the risk of injury.

Part II: Foundational strengthening

This segment of the program focuses on increasing leg strength and provide more stable knee joint. Technique is everything; close attention must be paid to the performance of these exercises so as to avoid injury. 

Part III: Movement coordination, deceleration, cutting, and plyometric training

These exercises are explosive and help to construct power, strength and speed. The most important component when considering performance technique is the landing. It must be soft! When landing from a jump transfer weight on the balls of feet slowly rolling back to the heel with a bent knee and a bent hip. These exercises are basic. However, it is important to perform them correctly. Start these exercise using a flat cone (2 inches) or with a visual line on the field.

[20]

The above video of on-field sport training program have been curated and published by JOSPT and provide a holistic program consistent with the recommendations of this clinical Practice guidelines for Exercise-Based Knee and Anterior Cruciate Ligament Injury Prevention. Recommended warm-up exercise sequence for athletes preparing to compete in field sports, such as soccer, football, lacrosse, field hockey, and softball etc.

Another Programs for reducing ACL injuries include HarmoKnee, FIFA 11+, Prevent Injury and Enhance Performance (PEP), and Sportsmetrics; and those used by Caraffa et al, and Olsen et al.

Fifa 11+, Harmoknee, PEP and Sportsmetric have their own Injury prevention program but what you would probably see in the table below is that no single program includes it all and from the CPG, that no single program was recommended as the number one program to follow.

Flexibility Running Strength plyometrics core Balance
Harmoknee Ö       Ö       Ö       Ö       Ö      
PEP Ö       Ö       Ö       Ö      
Sportsmetric Ö       Ö       Ö       Ö       Ö      
FIFA 11+ Ö       Ö       Ö       Ö      
Olsen et al Ö       Ö       Ö       Ö      
Achenbach et al Ö       Ö       Ö       Ö      
Caraffa et al Ö       Ö      
F-MARC 11+ Warm Up Program

Below is a brief outline of the key programs presented in this CPG along with outline of dosage of each exercise. 

FIFA 11+

The F-MARC 11+ program may be more effective at improving some risk factors for ACL injury among preadolescent female athletes than adolescent athletes, notably by reducing knee valgus angle and moment during a double-legged jump landing.[21]

PEP Program: Prevent injury and Enhance Performance 

The PEP (Prevent injury, Enhance Performance) Program is a highly specific 15 minute training session which mainly focuses on educating an athlete on strategies to prevent injury and includes specific exercises targeting issues as identified in previous research studies. 

1. Avoid vulnerable positions.

2. Increase flexibility.

3. Increase strength.

4. Include plyometric exercises in to the training program. 

5.Increase proprioception though agilities. [22] 

This prevention program comprises dynamic warm-up, flexibility, foundational strengthening, plyometrics, and sport specific agilities to deal with potential deficits in the strength and coordination of knee stabilizers. The coaches and trainers need to focus on correct posture, straight up and down jumps without excessive side-to-side movement, and reinforce soft landings. Optimally the program should be performed a minimum of 2-3 times per week during the season.

[23]

SPORTSMETRIC

  • Flexibility: Gastrocnemius and soleus, quadriceps, hamstrings, hip adductor, hip flexors, latissimus dorsi, posterior deltoid and pectoralis major.
  • Running: skipping, side shuffle and running. 
  • Strength: back hyperextension, leg press, calf raises, pull over, bench press, Latissimus dorsi pull down, forearm curl.
  • Core strength: abdominal curl. 
  • Plyometrics: wall jumps, tuck jumps, broad jumps with stick landing, squat jumps, double leg cone jumps side to side, back to front and 180 degrees, bounding in place, vertical jumps bounding for distance, scissor jumps, hop, hop and stick landing, step jump up vertical, mattress jumps, single leg jumps for distance, jump into bounding.[15]

Harmoknee

  • Flexibility: Standing calf stretch, standing quadricep stretch, half-kneeling hamstring stretch, half-kneeling hip flexor stretch, butterfly groin stretch and modified figure-four stretch.
  • Jogging: jogging, backwards jogging on toe, high knee skipping, defensive pressure (zig zig backwards), alternate forward zig zag and backward zig zag running. 
  • Strength: lunges, Nordic hamstring strengthening and single leg squat with toe raise.
  • Core stability: sit ups, plank on elbows and bridging.
  • Plyometrics: forward and backward double leg jumps, lateral single leg jumps, forward and backward single leg jumps, double leg jump with or without the ball.[16]

In summary, there is no single program to recommend as the best exercise-based injury prevention program and there are many valuable resources available online to implement such programs to help in training. Overall, there is a robust evidence to suggest these programs are highly effective in injury prevention for an ACL injury. In conclusion, the finding of the analysis demonstrated that ACL injury reduction programs decrease the risk of all ACL injuries by half and non‐contact ACL injuries in all athletes by two‐thirds in female athletes. [24] 

To successfully complete these prevention programs, time and commitment are most important. This CPG reinforces how important it is to teach our young athletes that these warms ups are the foundation for safe training and game play and to reduce the risk of injury, it is not an area we should compromise on. In fact, it might be the foremost valuable part of attending training and in the long run and keep people in the sport they love for longer.  

Neurocognitive Contributions to ACL injury

Neurocognition relates to a higher order of thinking or function in the brain. It includes but is not limited to the following -

  1. Executive functions - refers to the ability to coordinate motor, cognitive and emotional processess and play an important role in carrying out a task demanding attention as well as overriding the internal and external stimuli.
  2. Inhibitory control - refers to the ability to filter stimuli and focus on the task at hand. It relates to the working memory and plays an important role in the deployment of attention. It is required in tasks such as the rapidly changing environments on a football field.
  3. Cognitive flexibility - refers to the ability to adapt to changing conditions.
  4. Information Processing Speed - refers to the time required to process new information and retrieve data from memory. This is required to carry out complicated cognitive functions such as working memory.
  5. Reaction time - refers to the rapidness to respond to a stimuli
  6. Perception - refers to the ability to organize, identify, interpret, and understand the given information
  7. Dual or multi-tasking - refers to the ability to perform more than one action at a time

Expert athletes are those that combine motor and perceptual-cognitive skills. This addresses their ability to identify, locate and process information in a specific condition or environment. Team ball athletes like footballers and basketballers require rapid and efficient perceptive skills to interpret the opportunity to execute optimal performance like interpreting and identifying an opponent's movement before actually actioned. Errors in inhibitory control can lead to a faulty motor movement to fulfil the demand of sudden changes in action that can result in an ACL injury. Lacking the ability to switch focus can contribute to a loss of spatial awareness and disrupt motor control[25]. Studies have revealed changes or deficits in cognitive skills like reaction time, processing speed, and visual and verbal memory in ACL-injured athletes[26]. There have been advancements in noting changes in the central nervous system post ACL injury which should be noted and screening for neurocognitive factors should be implemented athletic population alongside the biomechanical factors. This has the potential to reduce the injury rate which can in turn decrease the years lost to disability.

Clinical Assessment Tools to Identify At‐Risk Athletes

The development of clinical assessment tools to identify athletes at risk for ACL injury would aid clinicians in targeting the populations that will benefit most from intervention. While some predictors of ACL injury are potentially modifiable (e.g. high knee abduction moment during landing tasks), these measurements require expensive measurement tools (e.g., motion analysis systems, force plates) and are labour‐intensive data collection and reduction techniques to identify important biomechanical risk factors.

Identification of athletes with high knee abduction moments is possible with less expensive equipment and time. These clinical prediction tools show moderate to high inter‐rater reliability (intra‐class correlation co‐efficiencies 0.60–0.97) and have continued to simplify and optimize the screening tools to include a calibrated physician's scale, a standard measuring tape, standard camcorder, Image software, and an isokinetic dynamometer. These optimized measures predict high knee abduction moments status with 84% sensitivity and 67% specificity. A clinician‐friendly nomogram tool demonstrates over 75% prediction accuracy for identification of high knee abduction moments in individual athletes. Creation of clinician‐friendly, inexpensive techniques to identify and subsequently enroll athletes into appropriate injury prevention programs may help reduce ACL injuries in athletes.[10]

Assess the Effectiveness of Intervention

Common assessment tools, such as the star excursion balance test, functional hop tests, strength measures, balance and stability measures and dynamometry and standard performance tests (e.g., power cleans, bench press, leg press) have been used to identify biomechanical and neuromuscular risk factors for ACL injury and provide measures of athletic performance. Assessments of the reliability of the assessment tools and performance measures have helped evaluate and optimize intervention strategies. Clinical assessment tools such as the tuck jump assessment and nomogram that predicts high knee abduction measures may also help rehabilitation specialists working with athletes to monitor functional deficits and determine level of readiness to meet the functional demands of sports with minimal risk of re‐injury.[10]

Clinical Bottom Line

In order to provide the injured athlete with the best care, physiotherapists should have in-depth knowledge of the anatomy and functioning of the ACL. The keystone to proper care of an ACL injury is obtaining the correct diagnosis within the first hour of injury before the development of significant hemarthrosis. This should also include the detection of and diagnosis of associated injuries.[27] Injury treatment and the return to activities for an individual is entirely dependent upon the ACL injury grade and any associated injuries.

Resources

References

  1. ↑ Nagano Y, Ida H, Akai M, Fukubayashi T. Biomechanical characteristics of the knee joint in female athletes during tasks associated with anterior cruciate ligament injury. The Knee. 2009 Mar 1;16(2):153-8.
  2. ↑ Arendt EA, Agel J,Dick R.Anterior cruciate ligament injury patterns among collegiate men and women. J Athl Train 1999;34:86-92.
  3. ↑ Garrick JG, Requa RK. Anterior cruciate ligament injuries in men and women: how common are they? In: Griffin LY, ed. Prevention of noncontact ACL injuries. Rosemont,IL:American Academy Orthopaedic Surgeons,2001:1-10.
  4. ↑ Agel J, Arendt E, Bershadsky B.Anterior cruciate ligament injury in national collegiate athletic association basketball and soccer: a 13 year review.Am J Sports Med 2005;33(4):524-30.
  5. ↑ Beynnon BD, Johnson RJ, Abate JA, Fleming BC, Nichols CE. Treatment of anterior cruciate ligament injuries, part I. The American journal of sports medicine. 2005 Oct;33(10):1579-602.
  6. ↑ Domnick C, Raschke MJ, Herbort M. Biomechanics of the anterior cruciate ligament: Physiology, rupture and reconstruction techniques. World journal of orthopedics. 2016 Feb 18;7(2):82.
  7. ↑ Traver JL, Kocher MS. Return-to-Sport Considerations in the Pre-Adolescent Athlete. InReturn to Sport after ACL Reconstruction and Other Knee Operations 2019 (pp. 593-605). Springer, Cham.
  8. ↑ Smith TO, Postle K, Penny F, McNamara I, Mann CJ. Is reconstruction the best management strategy for anterior cruciate ligament rupture? A systematic review and meta-analysis comparing anterior cruciate ligament reconstruction versus non-operative treatment. The Knee. 2014 Mar 1;21(2):462-70.
  9. ↑ Monk AP, Davies LJ, Hopewell S, Harris K, Beard DJ, Price AJ. Surgical versus conservative interventions for treating anterior cruciate ligament injuries. Cochrane Database of Systematic Reviews. 2016(4).
  10. ↑ 10.0 10.1 10.2 Hewett TE, Myer GD, Ford KR, Paterno MV, Quatman CE. Mechanisms, prediction, and prevention of ACL injuries: cut risk with three sharpened and validated tools. Journal of Orthopaedic Research. 2016 Nov;34(11):1843-55.
  11. ↑ 11.0 11.1 Sugimoto D, Myer GD, Bush HM, Klugman MF, McKeon JM, Hewett TE. Compliance with neuromuscular training and anterior cruciate ligament injury risk reduction in female athletes: a meta-analysis. Journal of athletic training. 2012;47(6):714-23.
  12. ↑ Alentorn-Geli E, Myer GD, Silvers HJ, Samitier G, Romero D, Lázaro-Haro C, Cugat R. Prevention of non-contact anterior cruciate ligament injuries in soccer players. Part 1: Mechanisms of injury and underlying risk factors. Knee surgery, sports traumatology, arthroscopy. 2009 Jul 1;17(7):705-29.
  13. ↑ Thompson JA, Tran AA, Gatewood CT, Shultz R, Silder A, Delp SL, Dragoo JL. Biomechanical effects of an injury prevention program in preadolescent female soccer athletes. The American journal of sports medicine. 2017 Feb;45(2):294-301.
  14. ↑ 14.0 14.1 Arundale AJ, Bizzini M, Giordano A, Hewett TE, Logerstedt DS, Mandelbaum B, Scalzitti DA, Silvers-Granelli H, Snyder-Mackler L, Altman RD, Beattie P. Exercise-based knee and anterior cruciate ligament injury prevention: clinical practice guidelines linked to the international classification of functioning, disability and health from the academy of orthopaedic physical therapy and the American Academy of sports physical therapy. Journal of Orthopaedic & Sports Physical Therapy. 2018 Sep;48(9):A1-42.
  15. ↑ 15.0 15.1 15.2 Hewett TE, Lindenfeld TN, Riccobene JV, Noyes FR. The effect of neuromuscular training on the incidence of knee injury in female athletes. The American journal of sports medicine. 1999 Nov;27(6):699-706.
  16. ↑ 16.0 16.1 Kiani A, Hellquist E, Ahlqvist K, Gedeborg R, Byberg L. Prevention of soccer-related knee injuries in teenaged girls. Archives of internal medicine. 2010 Jan 1;170(1):43-9.
  17. ↑ 17.0 17.1 Olsen OE, Myklebust G, Engebretsen L, Holme I, Bahr R. Exercises to prevent lower limb injuries in youth sports: cluster randomised controlled trial. BMJ. 2005;330:449
  18. ↑ Caraffa A, Cerulli G, Projetti M, Aisa G, Rizzo A. Prevention of anterior cruciate ligament injuries in soccer. A prospective controlled study of proprioceptive training. Knee Surg Sports Traumatol Arthrosc. 1996;4(1):19-21. doi: 10.1007/BF01565992. PMID: 8963746.
  19. ↑ Achenbach L, Krutsch V, Weber J, Nerlich M, Luig P, Loose O, Angele P, Krutsch W. Neuromuscular exercises prevent severe knee injury in adolescent team handball players. Knee surgery, sports traumatology, arthroscopy. 2018 Jul 1;26(7):1901-8.
  20. ↑ Knee injury prevention CPG: warm up exercise sequence for field sports Available from: https://youtube/RfROpda4kvg
  21. ↑ Thompson-Kolesar JA, Gatewood CT, Tran AA, Silder A, Shultz R, Delp SL, Dragoo JL. Age influences biomechanical changes after participation in an anterior cruciate ligament injury prevention program. The American journal of sports medicine. 2018 Mar;46(3):598-606.
  22. ↑ Mandelbaum BR, Silvers HJ, Watanabe DS, Knarr JF, Thomas SD, Griffin LY, Kirkendall DT, Garrett Jr W. Effectiveness of a neuromuscular and proprioceptive training program in preventing anterior cruciate ligament injuries in female athletes: 2-year follow-up. The American journal of sports medicine. 2005 Jul;33(7):1003-10.
  23. ↑ ACL injury prevention Exercises (PEP program) Available from:https://youtube/7Lag8uNU6AQ
  24. ↑ Webster KE, Hewett TE. Meta-analysis of meta-analyses of anterior cruciate ligament injury reduction training programs. J Orthop Res. 2018 Oct;36(10):2696-2708. doi: 10.1002/jor.24043. Epub 2018 Jun 13. PMID: 29737024.
  25. ↑ Gokeler A, Benjaminse A, Della Villa F, Tosarelli F, Verhagen E, Baumeister J. Anterior cruciate ligament injury mechanisms through a neurocognition lens: implications for injury screening. BMJ open sport & exercise medicine. 2021 May 1;7(2):e001091.
  26. ↑ Piskin D, Benjaminse A, Dimitrakis P, Gokeler A. Neurocognitive and neurophysiological functions related to ACL injury: a framework for neurocognitive approaches in rehabilitation and return-to-sports tests. Sports Health. 2022 Jul;14(4):549-55.
  27. ↑ Brukner, Khan. Clinical Sports Medicine. 3rd edition.Ch 27. Tata McGraw-Hill Publishing. New Delhi.


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